Enantioselective catalytic intramolecular cyclopropanation of allylic α-diazopropionates optimized with dirhodium(II) tetrakis[methyl 2-oxazolidinone-4(S or R)-carboxylate]
作者:Michael P. Doyle、Qi-Lin Zhou
DOI:10.1016/0957-4166(95)00289-2
日期:1995.9
High enantiocontrol, up to 85% ee, has been achieved in intramolecular cyclopropanation reactions of representative allylic alpha-diazopropionates with the catalytic uses of Rh-2(4S-MEOX)(4).
An efficient reductive Claisen rearrangement, catalyzed by in situ generated copper hydride and stoichiometric in diethoxymethylsilane, has been developed. Yields of up to 95 % with good to excellent diastereoselectivities were observed in this reaction. Mechanistic studies showed that the stereospecific rearrangement proceeded via a chair transition state of (E)‐silyl ketene acetals as intermediates
[reaction: see text] A catalytic amount of [(cod)RhCl](2) and MeDuPhos initiates an ester enolate Claisenrearrangement with good yields and diastereocontrol. Reaction conditions are mild and tolerant of base-sensitive functionality.