Enantioselective Pictet-Spengler-Type Cyclizations of Hydroxylactams: H-Bond Donor Catalysis by Anion Binding

摘要

N-Acyliminium ions are highly reactive electrophilic species that have been demonstrated only recently to engage successfully in asymmetric catalytic reactions. Our own studies in this area led to the discovery that the chiral thiourea derivative la promotes highly enantioselective Pictet—Spengler- and Mannich-type reactions through initial acylation of imines and isoquinolines, respectively. The process by which the resulting N-acyliminium ions are induced to undergo enantioselective additions with a simple hydrogen-bond donor catalyst such as la is intriguing.