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Catalytic syn ‐Selective Direct Aldol Reactions of Benzophenone Glycine Imine with Aromatic, Heteroaromatic and Aliphatic Aldehydes
Author(s) -
Lou Sha,
Ramirez Antonio,
Conlon David A.
Publication year - 2015
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.201400639
Subject(s) - aldol reaction , chemistry , benzophenone , imine , substituent , aldehyde , catalysis , medicinal chemistry , organic chemistry
We have developed highly diastereoselective silver‐catalyzed direct aldol reactions of benzophenone glycine imines with aromatic, heteroaromatic and aliphatic aldehydes. Protection of the secondary alcohol in the aldol product in situ with di‐ tert ‐butyl dicarbonate was applied to effectively circumvent the retro‐aldol process resulting in improved yields of the aldol products. Only a catalytic amount of base, lithium tert ‐butoxide, is required since tert ‐butoxide is regenerated during the Boc protection. Computational studies support a stereochemical model in which the axially‐oriented nitrogen atom of the imino ( Z )‐enolates coordinates the silver center in a boat conformation. The highly‐ordered transition states favor the formation of the syn aldol products due to the destabilizing interaction between the 1,3‐pseudoaxial alkoxyl group and the aldehyde substituent in the anti isomer.