Assinalação estereoquímica de produtos e descrição de mecanismos para reações de acoplamento entre α,α-diclorocetonas e compostos carbonílicos promovidas por brometo de índio(I)

Abstract

This work describes our results on the use of indium(I) bromide in Organic Synthesis, namely the reaction mechanisms and stereochemical outcome. Indium enolates, generated from the reaction between indium(I) bromide and α,α-dichloroketones, react with carbonyl compounds. The primary coupling with aldehydes leads to the diastereoselective synthesis of (syn+anti)-2-chloro-3-hydroxypropan- 1-ones, which can be converted to the respective trans-epoxyketones, exclusively. The indium(III) alkoxides of the 2-chloro-3-hydroxy-propan-1-ones are transformed into their (E)-prop-2-en-1-ones derivatives upon reaction with InBr according to a sequenced reaction mechanism. The most relevant feature of these reactions is that although the primary coupling with aldehydes affords a mixture of the two diastereoisomers of the indium(III) alkoxides, both the trans-epoxyketones and the E-enones were produced with rigorous stereoselectivity. These results are understood in terms of the enolate geometry (E or Z) and the retro-aldol reaction (kinetic/thermodynamic control) relating both forms of the enolate.