In discovery phase of the project, we have synthesised structurally different aziridine from as corresponding stilbene. In our investigation, benzyl diphenyl aziridine was subjected for cycloaddition reaction with CO2 using acridinium as visible light absorber organo-photoredox catalyst in acetonitrile using with blue led. However, in initial trials did not give the desired product. Therefore, we have attempted a set of experiment of aziridines with CO2 with different photoredox catalysis but in all cases same result was obtained. Activation of CO2 is a challenging task due to its kinetic and thermodynamic stable nature. Hence only a few methods, either by metal complexation or by organocatalysis, for its activation and transformation have been reported. At this stage, we have focused our work for activation of CO2 using nitrogen based organocatalysis. We have synthesised a chiral Guanidine based Organocatalyst and attempted the cycloaddition of aziridines with CO2 activated with chiral bicyclic guanidine catalyst, but similar results with formation of tri-benzyl amine were observed using different photocatalyst and solvent. Hence, in our further studies, we have modified the strategy by replacing the aziridines by 2H-aziridine and used the organo-photocatalytic conditions using visible light as energy source to trap the CO2. we have prepared the azirines by reported procedure and attempted a reaction of 2,3-diphenyl azirines with CO2 in acetonitrile the presence of acridinium as photocatalyst using blue LED of 456 nm. After irradiation of 6 hours surprisingly the formation of desired product was observed in moderate yield of 36 %. To check the generality of the reaction we have further move to test the reaction with 2(4-Methoxyphenyl)-3-phenyl-azirines with CO2 under same reaction conditions. It was our delight to isolate the product in similar yield. Currently we are working on this protocol with border substrate scope and their manipulation to biomolecules. During the investigation of cycloaddition of CO2 with aziridines the tri-phenyl aziridine was isolated as side product in a very low yield, which supports for formation of azomethine ylide intermediate. In continuation of our research work, we have envisioned to capture the azo-ylide by the use of dipolorophiles. To evaluate this hypothesis, we have attempted a reaction of triphenyl aziridine with dimethyl acetylene dicarboxylate (DMED) using DCA as photocatalyst in acetonitrile and it was delight to isolate the desired cycloadduct in good yield. To our delight, the aziridines having benzyl, methoxy benzyl, fluoro benzyl, aryl, and benzhydryl on nitrogen participated smoothly in the reaction to give the product in good yield. The generality of the cycloaddition of aziridines was also explored for the various alkenes as dipolorophiles. We have found that the dipolorophiles such as alkenes, aldehydes, di- aza compounds, melamides smoothly participate in the reaction and afford structurally different pyrrolidine, oxazolidine, and amino sulfonate.
The carboxylic acid is a privileged motif present in a large number of biologically active molecules. In the discovery phase of the project an photocarboxylation for synthesis of phenylacetic acid by use of CO2 and visible light has been developed by use of organophotoredox catalyst (4CzIPN) and different in combination with organic base. The feasibility and efficiency of reaction were studied under varying reaction conditions by use of different photoredox catalyst and solvent. . Applying these optimised conditions, we explored the scope for preparation of aryl and heteroaryl compounds with primary, secondary and tertiary benzylic carboxylic acids in moderate to good yields. The process was applicable to differently substituted DHPs, both with electron withdrawing and electron donating groups on the aryl ring, and also with different aryl and heteroaryl rings.
