Catalytic Enantioselective Intermolecular Hydroacylation: Rhodium-catalyzed Combination Of β-s-aldehydes And 1,3-disubstituted Allenes

摘要

Transition metal catalyzed alkene hydroacylation is an attractive method for the preparation of ketone derivatives; it is an atom economic process, employs readily available substrates, and can be achieved using relatively low catalyst loadings. Intramolecular variants, particularly those leading to the formation of cyclopen-tanones, have been extensively studied, and highly enantioselective variants have been developed. Intermolecular reactions are more challenging, due mainly to competitive metal-catalyzed reductive decarbonylation. One successful strategy to achieve these difficult transformations has been to stabilize the key acyl-metal intermediates using chelation control. Although this has resulted in a number of useful reactions, the scope of these processes is still relatively narrow, with a particular limitation being the ability to routinely use disubstituted alkenes. Given these difficulties it is not surprising that there is only a single report of enantioselective intermolecular hydroacylation, which, although efficient in terms of yield, offers only variable enantioselectivity. Allenes have been demonstrated to provide useful reactivity in a growing number of transition metal catalyzed processes, including enantioselective transformations, although their use in hydroacylation reactions is virtually unexplored. In this communication, we demonstrate that, by exchanging alkenes for allenes as substrates, an efficient and highly enantioselective catalytic intermolecular hydroacylation process can be achieved.