Hydrazide-Catalyzed Polyene Cyclization: Asymmetric Organocatalytic Synthesis of cis-Decalins
Samuel J Plamondon1, Josephine M Warnica1, Dainis Kaldre1
1Department of Chemistry, McGill University, 801 Sherbrooke W., Montreal, QC, H3A 0B8, Canada.
Abstract:
Polyene cyclizations offer rapid entry into terpenoid ring systems. Although enantioselective cyclizations of (E)-polyenes to form trans-decalin ring systems are well precedented, highly enantioselective cyclizations of (Z)-polyenes to form the corresponding cis-decalins have not been reported. Here, we describe the first application of iminium catalysis to the initiation of polyene cyclizations. Ethyl 1,2-diazepane-1-carboxylate catalyzes the cyclization of polyenes bearing enal initiators. Moreover, chiral bicyclic hydrazides catalyze the cyclizations of (Z)-polyene substrates to form cis-decalins with enantioselectivities of up to 97:3 er. DFT calculations suggest the catalysts promote the reaction by stabilizing positive charge as it develops during the bicyclization.
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