Final Report Summary - ENANTIOMEAR (Enantioselective Metal Enolate Alkylation Reactions Under Cooperative Lewis Base and Hydrogen-bond Donor)
1. INTRODUCTION:
The aldol reaction is one of the most powerful tools for the construction of β-hydroxy carbonyl compounds.1 The importance of these building blocks, contained in a wide variety of biologically relevant compounds, has promoted the development of several catalytic asymmetric methodologies for their production.2 However, despite enormous progress in the aldol addition arena, its application to the synthesis of tertiary alcohols still remains a major challenge, principally due to the lack of reactivity and the more difficult enantio-face differentiation of ketone electrophiles relative to the corresponding aldehydes. In addition, deleterious side reactions such as retro-aldol reactions can predominate when a ketone moiety is involved.3 Although a few catalytic asymmetric aldol reactions with unactivated ketones have been reported,4 the development of new and efficient catalytic asymmetric methodologies to access chiral tertiary alcohols remains an important goal in modern asymmetric catalysis.5 The catalytic asymmetric ketone aldol reaction of isocyanoacetate pronucleophiles6 could be a synthetically powerful approach. Isocyanoacetate ester addition reactions to carbonyl7 or imine electrophiles8,9 directly afford the respective oxazoline or imidazoline heterocycles which can be ring opened under mild hydrolytic conditions to afford the β-substituted-α-aminoacids derivatives. Although the catalytic asymmetric version of this reaction has been widely studied using aldehydes,7 to date, no enantioselective example using unactivated ketones has been reported despite its potential to provide an elegant asymmetric route to α-aminoacids derivatives possessing a chiral tertiary alcohol in the β-position.10 In a related study, the asymmetric aldol addition reaction of isothiocyanato esters and unactivated ketones affording oxazolidinethione products fully substituted at the β-stereocentre has been described.11
2. OBJETIVES OF THE PROJECT:
Recently, our group has developed an effective binary catalyst system comprising a ‘soft’ metal ion, such as Ag(I), and cinchona-derived amino-phosphine precatalyst. This system promotes the highly diastereo- and enantioselective isocyanoacetate aldehyde aldol reaction,7l and Mannich reactions of aldimines8e and ketimines.9a In conjunction with Ag(I) ions, these features provide remarkable catalytic activity in reactions of isocyanoacetate pronucleophiles and accordingly prompted us to address the challenging enantioselective aldol reaction of unactivated ketones. Herein we present our findings.
3. RESULTS:
Initially, the reaction of acetophenone and tert-butylisocyanoacetate in EtOAc at –20 °C was selected as a model and the performance of our previously described silver oxide/amino-phosphine catalyst system, which was employed as 2:1 molar ratio of amino-phosphine ligand to metal, was assessed.7l The reaction conditions (temperature, solvent and time), the silver source and the amino-phosphine ligand were optimized. We can determinate that the reaction between acetophenone and tert-butylisocyanoacetate in EtOAc, at -20 ºC using 10 mol% of quinine-derived amino-phosphine and 2.5 mol% of Ag2O, allow to obtain major trans-oxazoline compound with very good diastereo and enantioseletivities (dr = 95:5, 89%ee).
Subsequently, the effect of lowering the catalyst loading was studied. Using the same starting materials, the trans-oxazoline compound was obtained with marginally lower levels of enantioselectivity when the loading was reduced to 5 and 1 mol% of quinine-derived amino-phosphine whilst maintaining a 2:1 ratio of precatalyst to metal. However, diastereo- and enantioselectivities comparable to the best result were restored when a 1:1 ratio of precatalyst to Ag(I) was employed at 5 mol% of quinine-derived amino-phosphine.
With the optimal conditions established, we proceeded to study the scope of the reaction using tert-butyl isocyanoacetate and different alkyl aryl ketones, catalysed by quinine-derived amino phosphine precatalyst and Ag2O. Several substituted methyl aryl ketones possessing either electron-withdrawing or electron-donating groups afforded the major trans-oxazolines with good diastereoselectivities and moderate to very good enantioselectivities (93:7-96:4 er). Pleasingly 5- and 6-membered ring heteroaromatic methyl ketone substrates were also well-tolerated in the reaction giving products with good stereoselectivities in both cases. An important success was observed when aryl ethyl ketones were used in the reaction. Major trans-oxazolines compounds were obtained with good diastereoselectivities and excellent enantioselectivities (98:2-99:1 er). Aryl propyl ketones were also excellent substrates and afforded the trans-oxazoline products in high yields and in good to excellent enantioselectivities. Finally isovalerophenone afforded the trans-oxazoline product in 75% yield, 96:4 dr and in 97:3 er demonstrating the broad scope of the reaction with different non-activated ketones. We also demonstrated the scope of the reaction with different isocyanoacetates. Using ethyl isocyanoacetate or methyl isocyanoacetate the trans-oxazoline products were obtained with very good diastereoselectivities and excellent enantioselectivities. Unfortunately, under the optimized conditions symmetrical and unsymmetrical aliphatic ketones, afforded oxazoline products with poor enantioselectivities.
As the stereochemical outcome favoured the production of the trans-oxazoline product, and as alkyl groups larger than a methyl group were well-tolerated in the ketone aldol reaction, an opportunity to apply our chemistry to the synthesis of oxazoline-fused γ- and β-lactam products arose. Thus ketones with an azide group in γ and β position were subjected to the standard reaction conditions and pleasingly oxazolines products were afforded in good yield and with excellent enantioselectivities. Subsequently, under standard Staudinger conditions these oxazolines were transformed in a straightforward manner into the target lactam products in high yields without compromising stereochemical integrity.
To demonstrate further synthetic utility whilst adding to the literature knowledge on the hydrolytic manipulation of oxazoline heterocycles,12 we subsequently explored the conversion of product oxazolines to the corresponding amino acid derivative using different reaction conditions. The hydrolysis of one of our oxazoline using catalytic amounts of HCl afforded the corresponding N-formyl derivative in quantitative yield. Similarly, the methanolysis of another oxazoline compound led to the corresponding β-hydroxy-α-amino acid tert butyl ester under mild conditions. These transformations show the ability of our method to afford protected serine-derivatives doubly substituted at the β-position. Furthermore, treatment of with thiophosgene under basic conditions furnished the crystalline oxazolidinethione, which allowed its absolute and relative stereochemical configuration to be determined by single crystal X-ray diffraction and that of the other oxazolines products to be assigned by analogy.
Based on previous reports9b, 13 and on the known absolute stereochemical configuration of oxazoline products , a transition state model rationalizing the stereochemical outcome of the ketone aldol reaction between acetophenone and tert-butylisocyanoacetate using quinine-derived amino-phosphine and silver oxide is proposed. In the enantiodetermining carbon-carbon bond-forming step, the phosphorous and amide nitrogen atoms from the quinine-derived amino-phosphine, the oxygen from the ketone and the terminal carbon atom of the isonitrile coordinate to silver (I) in a tetrahedral manner. Additional transition state stabilization is provided through H-bonding of the protonated quinuclidine to the coordinated ketone oxygen atom. Importantly this interaction creates a well-defined chiral pocket that can readily differentiate the enantiotopic faces of the bound ketone; unfavourable steric interactions force the aryl group away from the quinuclidine and preferential attack of the enolate to the Re face occurs.
5. CONCLUSIONS:
In conclusion, in this project we have developed the first highly enantio- and diastereoselective aldol addition/cyclization reaction of isocyanoacetate esters with unactivated prochiral ketones to afford functionalized oxazolines possessing a fully substituted stereogenic center at the β-carbon. The reaction is efficient and broad in scope and efficiently promoted using a binary catalyst system comprising a cinchona-derived aminophosphine precatalyst and silver oxide. Following hydrolytic manipulation of oxazoline heterocycles, the new chemistry enables the transformation of simple ketones into the corresponding amino acid derivatives possessing a tertiary alcohol in the β position. These results were published on Angewandte Chemie Internantional Edition; DOI: 10.1002/anie.201411852.
[1] Reviews on asymmetric aldol reactions: a) R. Mahrwald, in Modern Aldol Reaction, WILEY-VCH, 2004. b) B. M. Trost, C. S. Brindle, Chem. Soc. Rev. 2010, 39, 1600-1632. c) C. Palomo, M. Oiarbide, J. M. García, Chem. Soc. Rev. 2004, 33, 65-75. d) L. M. Geary, P. G. Hultin, Tetrahedron: Asymmetry 2009, 20, 131-173.
[2] a) K. C. Nicolau, C. N. C. Boddy, S. Bräse, N. Winssinger, Angew. Chem. Int. Ed. 1999, 38, 2096-2152. b) M. K. Renner, Y. Shen, X. Cheng, P. R. Jensen, W. Frankmoelle, C. A. Kauffman, W. Fenical, E. Lobkovsky, J. Clardy, J. Am. Chem. Soc. 1999, 121, 11273-11276. c) B. Herbert, I. H. Kim, K. L. Kirk, J. Org. Chem. 2001, 66, 4892-4897.
[3] a) J. P. Guthrie, J. Am. Chem. Soc. 1991, 113, 7249-7255. b) M. Hatano, E. Takagi, K. Ishihara, Org. Lett 2007, 9, 4527-4530.
[4] For Lewis base catalysis see: a) S. E. Denmark, Y. Fan, J. Am. Chem. Soc. 2002, 124, 4233-4235. b) S. E. Dernmark, Y. Fan, M. D. Eastgate, J. Org. Chem. 2005, 70, 5235-5248. For reaction with enolsilanes see: c) K. Oisaki, D. Zhao, M. Kanai, M. Shibasaki, J. Am. Chem. Soc. 2006, 128, 7164-7165. b) K. Oisaki, Y. Suto, M. Kanai, M. Shibasaki, J. Am. Chem. Soc. 2003, 125, 5644-5645. e) X. Moreau, B. Bazan-Tejada, J. Campagne, J. Am. Chem. Soc. 2005, 127, 7288-7289. For reductive aldol reaction see: f) H. W. Laim, P. M. Joesnsuu, Org. Lett. 2005, 7, 4225-4228. g) J. Deschamp, O. Chuzel, J. Hannedouche, O. Riant, Angew. Chem. Int. Ed. 2006, 45, 1292-1297. See also: e) S. Adachi, T. Harada, Eur. J. Org. Chem. 2009, 3661-3671.
[5] a) E. J. Corey, A. Guzman-Perez, Angew. Chem. Int. Ed. 1998, 37, 388-401. b) O. Riant, J. Hannedouche, Org. Biomol. Chem. 2005, 5, 873-888. c) P. G. Cozzi, R. Hilgraf, N. Zimmermann, Eur. J. Org. Chem. 2007, 5969-5994. d) M. Shibasaki, M. Kanai, Chem. Rev. 2008, 108, 2853-2873. e) M. Hatano, K. Ishihara, Synthesis 2008, 1647-1675.
[6] Review on isocyanoacetates: a) A. V. Gulevich, A. G. Zhdanko, R. V. A. Orru, V. G. Nenajdenko, Chem. Rev. 2010, 110, 5235-5331. See also: b) W. A. Böl, F. Gerhart, A. Nürrenbach, U. Schöllkopf, Angew. Chem. Int. Ed. 1970, 9, 458-459. c) Y. Ito, T. Matsuura, T. Saegusa, Tetrahedron Lett. 1985, 26, 5781-5784.
[7] For enantioselective reactions of aldehydes: a) Y. Ito, M. Sawamura, T. Hayashi J. Am. Chem. Soc. 1986, 108, 6405-6406. b) Y. Ito, M. Sawamura, T. Hayashi Tetrahedron Lett. 1987, 28, 6215-6218. c) S. D. Pastor, A. Togni J. Am. Chem. Soc. 1989, 111, 2333-2334. d) T. Hayashi, Y. Uozumi, A. Yamzaki, M. Sawamura, H. Hamashima, Y. Ito Tetrahedron Lett. 1991, 32, 2799-2802. e) T. Hayashi, M. Sawamura, Y. Ito Tetrahedron 1992, 48, 1999-2012. f) V. A. Soloshonok, T. Hayashi, Tetrahedron Lett. 1994, 35, 2713-2716. g) V. A. Soloshonok, A. Kacharov, T. Hayashi Tetrahedron 1996, 52, 245-254. h) J. M. Longmire, X. Zhang Organometallics 1998, 17, 4374-4379. i) M. Sawamura, Y. Nakayama, T. Kato, Y. Ito, J. Org. Chem. 2005, 60, 1727-1732. j) S. Gosiewska, M. H. Veld, J. J. M. de Pater, P. C. A. Bruinjnincx, M. Lutz, A. L. Spek, G. van Koten, R. J. M. K. Gebbink Tetrahedron Asymmetry 2006, 17, 674-686. k) M. Xue, C. Guo, L. Gong, Synlett 2009, 13, 2191-2197. l) H. Y. Kim, K. Oh Org. Lett. 2011, 13, 1306-1309. m) F. Sladojevich, A. Trabocchi, A. Guarna, D. J. Dixon, J. Am. Chem. Soc. 2011, 133, 1710-1713.
[8] For enantioselective reactions of aldimines: a) X. Zhou, Y. Lin, L. Dai, J. Sun, L. Xia, M. Tang J. Org. Chem. 1999, 64, 1331-1334. b) X. Zhou, Y. Lin, L. Dai Tetrahedron Asymmetry 1999, 10, 855-862. c) J. Aydin, A. Ryden, K. J. Szabó Tetrahedron Asymmetry 2008, 19, 1867-1870. d) Z. Zhang, G. Lu, M. Chen, N. Lin, Y. Li, T. Hayashi, A. S. C. Chan Tetrahedron Asymmetry 2010, 21, 1715-1721. e) P. Shao, J. Liao, Y. A. Ho, Y. Zhao Angew. Chem. Int. Ed. 2014, 53, 5435-5439.
[9] For enantioselective reactions of ketimines: a) I. Ortín, D. J. Dixon, Angew. Chem. Int. Ed. 2014, 53, 3462-3465. b) M. Hayashi, M. Iwanaga, N. Shiomi, D. Nakane, H. Masuda, S. Nakamura Angew. Chem. Int. Ed. 2014, 53, 8411-8415.
[10] For the racemic reaction, see: a) V. A. Soloshonok, A. D. Kacharov, D. V. Avilov, T. Hayashi, Tetrahedron Lett. 1996, 37, 7845-7848. b) V. A. Soloshonok, A. D. Kacharov, D. V. Avilov, K. Ishikawa, N. Nagashima, T. Hayashi, J. Org. Chem. 1997, 62, 3470-3479.
[11] a) T. Yoshino, H. Morimoto, G. Lu, S. Matsunaga, M. Shibasaki, J. Am. Chem. Soc. 2009, 131, 17082-17083. b) S. Matsunaga, T. Yoshino, The Chemical Record 2011, 11, 260-268.
[12] D. Hoppe, U. Schöllkopf, Angew. Chem. Int. Ed. 1972, 11, 432-433.
[13] a) W. Zeng, G. Chen, Y. Zhou, Y. Li, J. Am. Chem. Soc. 2007, 129, 750-751. b) G. Liang, M. Tong, C. Wang, Adv. Synth. Catal. 2009, 351, 3101-3106. c) J. Song, C. Guo, P. Chen, J. Yu, S. Luo, L. Gong, Chem. Eur. J. 2011, 17, 7786-7790.
The aldol reaction is one of the most powerful tools for the construction of β-hydroxy carbonyl compounds.1 The importance of these building blocks, contained in a wide variety of biologically relevant compounds, has promoted the development of several catalytic asymmetric methodologies for their production.2 However, despite enormous progress in the aldol addition arena, its application to the synthesis of tertiary alcohols still remains a major challenge, principally due to the lack of reactivity and the more difficult enantio-face differentiation of ketone electrophiles relative to the corresponding aldehydes. In addition, deleterious side reactions such as retro-aldol reactions can predominate when a ketone moiety is involved.3 Although a few catalytic asymmetric aldol reactions with unactivated ketones have been reported,4 the development of new and efficient catalytic asymmetric methodologies to access chiral tertiary alcohols remains an important goal in modern asymmetric catalysis.5 The catalytic asymmetric ketone aldol reaction of isocyanoacetate pronucleophiles6 could be a synthetically powerful approach. Isocyanoacetate ester addition reactions to carbonyl7 or imine electrophiles8,9 directly afford the respective oxazoline or imidazoline heterocycles which can be ring opened under mild hydrolytic conditions to afford the β-substituted-α-aminoacids derivatives. Although the catalytic asymmetric version of this reaction has been widely studied using aldehydes,7 to date, no enantioselective example using unactivated ketones has been reported despite its potential to provide an elegant asymmetric route to α-aminoacids derivatives possessing a chiral tertiary alcohol in the β-position.10 In a related study, the asymmetric aldol addition reaction of isothiocyanato esters and unactivated ketones affording oxazolidinethione products fully substituted at the β-stereocentre has been described.11
2. OBJETIVES OF THE PROJECT:
Recently, our group has developed an effective binary catalyst system comprising a ‘soft’ metal ion, such as Ag(I), and cinchona-derived amino-phosphine precatalyst. This system promotes the highly diastereo- and enantioselective isocyanoacetate aldehyde aldol reaction,7l and Mannich reactions of aldimines8e and ketimines.9a In conjunction with Ag(I) ions, these features provide remarkable catalytic activity in reactions of isocyanoacetate pronucleophiles and accordingly prompted us to address the challenging enantioselective aldol reaction of unactivated ketones. Herein we present our findings.
3. RESULTS:
Initially, the reaction of acetophenone and tert-butylisocyanoacetate in EtOAc at –20 °C was selected as a model and the performance of our previously described silver oxide/amino-phosphine catalyst system, which was employed as 2:1 molar ratio of amino-phosphine ligand to metal, was assessed.7l The reaction conditions (temperature, solvent and time), the silver source and the amino-phosphine ligand were optimized. We can determinate that the reaction between acetophenone and tert-butylisocyanoacetate in EtOAc, at -20 ºC using 10 mol% of quinine-derived amino-phosphine and 2.5 mol% of Ag2O, allow to obtain major trans-oxazoline compound with very good diastereo and enantioseletivities (dr = 95:5, 89%ee).
Subsequently, the effect of lowering the catalyst loading was studied. Using the same starting materials, the trans-oxazoline compound was obtained with marginally lower levels of enantioselectivity when the loading was reduced to 5 and 1 mol% of quinine-derived amino-phosphine whilst maintaining a 2:1 ratio of precatalyst to metal. However, diastereo- and enantioselectivities comparable to the best result were restored when a 1:1 ratio of precatalyst to Ag(I) was employed at 5 mol% of quinine-derived amino-phosphine.
With the optimal conditions established, we proceeded to study the scope of the reaction using tert-butyl isocyanoacetate and different alkyl aryl ketones, catalysed by quinine-derived amino phosphine precatalyst and Ag2O. Several substituted methyl aryl ketones possessing either electron-withdrawing or electron-donating groups afforded the major trans-oxazolines with good diastereoselectivities and moderate to very good enantioselectivities (93:7-96:4 er). Pleasingly 5- and 6-membered ring heteroaromatic methyl ketone substrates were also well-tolerated in the reaction giving products with good stereoselectivities in both cases. An important success was observed when aryl ethyl ketones were used in the reaction. Major trans-oxazolines compounds were obtained with good diastereoselectivities and excellent enantioselectivities (98:2-99:1 er). Aryl propyl ketones were also excellent substrates and afforded the trans-oxazoline products in high yields and in good to excellent enantioselectivities. Finally isovalerophenone afforded the trans-oxazoline product in 75% yield, 96:4 dr and in 97:3 er demonstrating the broad scope of the reaction with different non-activated ketones. We also demonstrated the scope of the reaction with different isocyanoacetates. Using ethyl isocyanoacetate or methyl isocyanoacetate the trans-oxazoline products were obtained with very good diastereoselectivities and excellent enantioselectivities. Unfortunately, under the optimized conditions symmetrical and unsymmetrical aliphatic ketones, afforded oxazoline products with poor enantioselectivities.
As the stereochemical outcome favoured the production of the trans-oxazoline product, and as alkyl groups larger than a methyl group were well-tolerated in the ketone aldol reaction, an opportunity to apply our chemistry to the synthesis of oxazoline-fused γ- and β-lactam products arose. Thus ketones with an azide group in γ and β position were subjected to the standard reaction conditions and pleasingly oxazolines products were afforded in good yield and with excellent enantioselectivities. Subsequently, under standard Staudinger conditions these oxazolines were transformed in a straightforward manner into the target lactam products in high yields without compromising stereochemical integrity.
To demonstrate further synthetic utility whilst adding to the literature knowledge on the hydrolytic manipulation of oxazoline heterocycles,12 we subsequently explored the conversion of product oxazolines to the corresponding amino acid derivative using different reaction conditions. The hydrolysis of one of our oxazoline using catalytic amounts of HCl afforded the corresponding N-formyl derivative in quantitative yield. Similarly, the methanolysis of another oxazoline compound led to the corresponding β-hydroxy-α-amino acid tert butyl ester under mild conditions. These transformations show the ability of our method to afford protected serine-derivatives doubly substituted at the β-position. Furthermore, treatment of with thiophosgene under basic conditions furnished the crystalline oxazolidinethione, which allowed its absolute and relative stereochemical configuration to be determined by single crystal X-ray diffraction and that of the other oxazolines products to be assigned by analogy.
Based on previous reports9b, 13 and on the known absolute stereochemical configuration of oxazoline products , a transition state model rationalizing the stereochemical outcome of the ketone aldol reaction between acetophenone and tert-butylisocyanoacetate using quinine-derived amino-phosphine and silver oxide is proposed. In the enantiodetermining carbon-carbon bond-forming step, the phosphorous and amide nitrogen atoms from the quinine-derived amino-phosphine, the oxygen from the ketone and the terminal carbon atom of the isonitrile coordinate to silver (I) in a tetrahedral manner. Additional transition state stabilization is provided through H-bonding of the protonated quinuclidine to the coordinated ketone oxygen atom. Importantly this interaction creates a well-defined chiral pocket that can readily differentiate the enantiotopic faces of the bound ketone; unfavourable steric interactions force the aryl group away from the quinuclidine and preferential attack of the enolate to the Re face occurs.
5. CONCLUSIONS:
In conclusion, in this project we have developed the first highly enantio- and diastereoselective aldol addition/cyclization reaction of isocyanoacetate esters with unactivated prochiral ketones to afford functionalized oxazolines possessing a fully substituted stereogenic center at the β-carbon. The reaction is efficient and broad in scope and efficiently promoted using a binary catalyst system comprising a cinchona-derived aminophosphine precatalyst and silver oxide. Following hydrolytic manipulation of oxazoline heterocycles, the new chemistry enables the transformation of simple ketones into the corresponding amino acid derivatives possessing a tertiary alcohol in the β position. These results were published on Angewandte Chemie Internantional Edition; DOI: 10.1002/anie.201411852.
[1] Reviews on asymmetric aldol reactions: a) R. Mahrwald, in Modern Aldol Reaction, WILEY-VCH, 2004. b) B. M. Trost, C. S. Brindle, Chem. Soc. Rev. 2010, 39, 1600-1632. c) C. Palomo, M. Oiarbide, J. M. García, Chem. Soc. Rev. 2004, 33, 65-75. d) L. M. Geary, P. G. Hultin, Tetrahedron: Asymmetry 2009, 20, 131-173.
[2] a) K. C. Nicolau, C. N. C. Boddy, S. Bräse, N. Winssinger, Angew. Chem. Int. Ed. 1999, 38, 2096-2152. b) M. K. Renner, Y. Shen, X. Cheng, P. R. Jensen, W. Frankmoelle, C. A. Kauffman, W. Fenical, E. Lobkovsky, J. Clardy, J. Am. Chem. Soc. 1999, 121, 11273-11276. c) B. Herbert, I. H. Kim, K. L. Kirk, J. Org. Chem. 2001, 66, 4892-4897.
[3] a) J. P. Guthrie, J. Am. Chem. Soc. 1991, 113, 7249-7255. b) M. Hatano, E. Takagi, K. Ishihara, Org. Lett 2007, 9, 4527-4530.
[4] For Lewis base catalysis see: a) S. E. Denmark, Y. Fan, J. Am. Chem. Soc. 2002, 124, 4233-4235. b) S. E. Dernmark, Y. Fan, M. D. Eastgate, J. Org. Chem. 2005, 70, 5235-5248. For reaction with enolsilanes see: c) K. Oisaki, D. Zhao, M. Kanai, M. Shibasaki, J. Am. Chem. Soc. 2006, 128, 7164-7165. b) K. Oisaki, Y. Suto, M. Kanai, M. Shibasaki, J. Am. Chem. Soc. 2003, 125, 5644-5645. e) X. Moreau, B. Bazan-Tejada, J. Campagne, J. Am. Chem. Soc. 2005, 127, 7288-7289. For reductive aldol reaction see: f) H. W. Laim, P. M. Joesnsuu, Org. Lett. 2005, 7, 4225-4228. g) J. Deschamp, O. Chuzel, J. Hannedouche, O. Riant, Angew. Chem. Int. Ed. 2006, 45, 1292-1297. See also: e) S. Adachi, T. Harada, Eur. J. Org. Chem. 2009, 3661-3671.
[5] a) E. J. Corey, A. Guzman-Perez, Angew. Chem. Int. Ed. 1998, 37, 388-401. b) O. Riant, J. Hannedouche, Org. Biomol. Chem. 2005, 5, 873-888. c) P. G. Cozzi, R. Hilgraf, N. Zimmermann, Eur. J. Org. Chem. 2007, 5969-5994. d) M. Shibasaki, M. Kanai, Chem. Rev. 2008, 108, 2853-2873. e) M. Hatano, K. Ishihara, Synthesis 2008, 1647-1675.
[6] Review on isocyanoacetates: a) A. V. Gulevich, A. G. Zhdanko, R. V. A. Orru, V. G. Nenajdenko, Chem. Rev. 2010, 110, 5235-5331. See also: b) W. A. Böl, F. Gerhart, A. Nürrenbach, U. Schöllkopf, Angew. Chem. Int. Ed. 1970, 9, 458-459. c) Y. Ito, T. Matsuura, T. Saegusa, Tetrahedron Lett. 1985, 26, 5781-5784.
[7] For enantioselective reactions of aldehydes: a) Y. Ito, M. Sawamura, T. Hayashi J. Am. Chem. Soc. 1986, 108, 6405-6406. b) Y. Ito, M. Sawamura, T. Hayashi Tetrahedron Lett. 1987, 28, 6215-6218. c) S. D. Pastor, A. Togni J. Am. Chem. Soc. 1989, 111, 2333-2334. d) T. Hayashi, Y. Uozumi, A. Yamzaki, M. Sawamura, H. Hamashima, Y. Ito Tetrahedron Lett. 1991, 32, 2799-2802. e) T. Hayashi, M. Sawamura, Y. Ito Tetrahedron 1992, 48, 1999-2012. f) V. A. Soloshonok, T. Hayashi, Tetrahedron Lett. 1994, 35, 2713-2716. g) V. A. Soloshonok, A. Kacharov, T. Hayashi Tetrahedron 1996, 52, 245-254. h) J. M. Longmire, X. Zhang Organometallics 1998, 17, 4374-4379. i) M. Sawamura, Y. Nakayama, T. Kato, Y. Ito, J. Org. Chem. 2005, 60, 1727-1732. j) S. Gosiewska, M. H. Veld, J. J. M. de Pater, P. C. A. Bruinjnincx, M. Lutz, A. L. Spek, G. van Koten, R. J. M. K. Gebbink Tetrahedron Asymmetry 2006, 17, 674-686. k) M. Xue, C. Guo, L. Gong, Synlett 2009, 13, 2191-2197. l) H. Y. Kim, K. Oh Org. Lett. 2011, 13, 1306-1309. m) F. Sladojevich, A. Trabocchi, A. Guarna, D. J. Dixon, J. Am. Chem. Soc. 2011, 133, 1710-1713.
[8] For enantioselective reactions of aldimines: a) X. Zhou, Y. Lin, L. Dai, J. Sun, L. Xia, M. Tang J. Org. Chem. 1999, 64, 1331-1334. b) X. Zhou, Y. Lin, L. Dai Tetrahedron Asymmetry 1999, 10, 855-862. c) J. Aydin, A. Ryden, K. J. Szabó Tetrahedron Asymmetry 2008, 19, 1867-1870. d) Z. Zhang, G. Lu, M. Chen, N. Lin, Y. Li, T. Hayashi, A. S. C. Chan Tetrahedron Asymmetry 2010, 21, 1715-1721. e) P. Shao, J. Liao, Y. A. Ho, Y. Zhao Angew. Chem. Int. Ed. 2014, 53, 5435-5439.
[9] For enantioselective reactions of ketimines: a) I. Ortín, D. J. Dixon, Angew. Chem. Int. Ed. 2014, 53, 3462-3465. b) M. Hayashi, M. Iwanaga, N. Shiomi, D. Nakane, H. Masuda, S. Nakamura Angew. Chem. Int. Ed. 2014, 53, 8411-8415.
[10] For the racemic reaction, see: a) V. A. Soloshonok, A. D. Kacharov, D. V. Avilov, T. Hayashi, Tetrahedron Lett. 1996, 37, 7845-7848. b) V. A. Soloshonok, A. D. Kacharov, D. V. Avilov, K. Ishikawa, N. Nagashima, T. Hayashi, J. Org. Chem. 1997, 62, 3470-3479.
[11] a) T. Yoshino, H. Morimoto, G. Lu, S. Matsunaga, M. Shibasaki, J. Am. Chem. Soc. 2009, 131, 17082-17083. b) S. Matsunaga, T. Yoshino, The Chemical Record 2011, 11, 260-268.
[12] D. Hoppe, U. Schöllkopf, Angew. Chem. Int. Ed. 1972, 11, 432-433.
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