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Metal-free organic chemistry

Synthetic chemistry has not yet emulated the levels of selectivity and efficiency achieved by enzymes; but this status quo will soon change thanks to the efforts of EU-funded researchers.
Metal-free organic chemistry
The M-FOOS (Metal-free oxidants in organic synthesis) project developed a fresh approach to organic chemistry using new carbon-based and metal-free agents. These agents radically changed the way key oxidative transformations were accomplished, making them more powerful and user-friendly.

Hypervalent iodine reagents are widely used in organic synthesis as their chemistry is analogous to that found in transition metal complexes. Under suitable conditions they may be employed as less toxic and safer replacements for heavy metal oxidants. M-FOOS therefore studied hypervalent iodine reagents and the contributions that they can make to organic synthesis.

Researchers developed a simple yet powerful catalytic technique for styrene dimerisation using the solvent hexafluoroisopropanol (HFIP) to rapidly form unsymmetrical tetra-substituted cyclobutanes. HFIP is employed as an additive to enhance or alter the selectivity of certain important reactions.

Electrochemical experiments showed that the enhanced reactivity of the initiator phenyliodine (III) diacetate (PIDA) in HFIP is due to the greater oxidising abilities found in this fluorinated solvent. In HFIP, the reactivity of PIDA is comparable, or even better, than its fluorinated analogue phenyliodine (III) bis(trifluoroacetate) (PIFA). This result contrasted with the traditional view that fluoroalcohol can stabilise a radical cation formed by single electron transfer.

Nuclear magnetic resonance (NMR) experiments revealed the formation of a strong hydrogen-bonded adduct between the solvent and oxidising reagent. Additional evidence was provided by nuclear Overhauser effect (nOe) and diffusion-ordered spectroscopy experiments. They confirmed the existence of a hydrogen-bonded species upon mixing both hydrogen-donor HFIP and hydrogen acceptor PIDA.

The chemical compound osmium tetroxide (OsO4) has many uses including the syn-dihydroxylation of alkenes, despite its toxicity and the rareness of osmium. Scientists addressed this problem by investigating a new metal-free dihydroxylation procedure based on 2,2,6,6-tetramethylpiperidin-1-yloxy (commonly known as TEMPO). This led to a new process that incorporated both TEMPO and an external nucleophile (or the solvent in its absence).

M-FOOS results will have a significant international impact within the field of organic chemistry. It is of particular interest to those in academia and the chemical and pharmaceutical industries aiming to develop more sustainable technologies.

Related information

Keywords

M-FOOS, hypervalent iodine reagents, hexafluoroisopropanol, initiator phenyliodine (III) diacetate, phenyiodine (III) bis(trifluoroacetate)
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