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Secondary Amine‐Catalyzed Asymmetric γ ‐Alkylation of α ‐Branched Enals via Dienamine Activation
Author(s) -
Silvi Mattia,
Cassani Carlo,
Moran Antonio,
Melchiorre Paolo
Publication year - 2012
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.201200412
Subject(s) - chemistry , alkylation , enantioselective synthesis , amine gas treating , catalysis , selectivity , organocatalysis , organic chemistry , silyl ether , stereochemistry , silylation
The direct and enantioselective γ ‐alkylation of α ‐substituted α , β ‐unsaturated aldehydes proceeding under dienamine catalysis is described. We have found that the Seebach modification of the diphenyl‐prolinol silyl ether catalyst in combination with saccharin as an acidic additive promotes an S N 1 alkylation pathway, while ensuring complete γ ‐site selectivity and a high stereocontrol. Theoretical and spectroscopic investigations have provided insights into the conformational behavior of the covalent dienamine intermediate derived from the condensation of 2‐methylpent‐2‐enal and the chiral amine. Implications for the mechanism of stereoinduction are discussed.