The key for establishing this protocol is the distinct ability of the iminophosphorane catalyst to precisely direct the equilibrium mixture of the enediolates toward the intermolecular carbon-carbonbondformation with simultaneous yet rigorous control of relative and absolute stereochemistry. The critical importance of the cyclohexyl substituents on the catalyst backbone in dictating the reaction
only traces of the product were observed under these conditions (2 x). When primary or secondary alkyl thioethers were used instead of aromatic thioethers, lower yields and significant decreases in the enantioselectivities were obtained (2 p, 2 q, 2 r, and 2 s). In the case of tert-butyl thioether, a good enantiomeric excess of 82% was obtained, but this was accompanied by a very poor yield of 18% (2 t)
Enantioselective Organocatalytic Rearrangement of α-Acyloxy- β-keto Sulfides to α-Acyloxy Thioesters
作者:Francesca Capitta、Angelo Frongia、Pier Paolo Piras、Patrizia Pitzanti、Francesco Secci
DOI:10.1002/adsc.201000376
日期:2010.11.22
The first highly enantioselectiveorganocatalyticrearrangement of α-acyloxy-β-keto sulfides to α-acyloxy thioesters has been developed which provides a number of important synthetic building blocks in high yield and with excellent enantioselectivities (ee: up to 92%).