Experimental Studies on the Selective beta-C-H Halogenation of Enones

摘要

Here we describe the realization of a one-pot protocol for the beta-C-H halogenation of cyclic enones via umpolung of the beta-carbon. The developed method includes hydrazone formation and selective beta-halogenation (bromination, chlorination) with N-bromosuccinimide and Palauchlor (2-chloro-1,3-bis(methoxycarbonyl)guanidine) followed by hydrolysis of the hydrazone moiety. Using the optimized conditions, we were able to effectively beta-brominate and beta-chlorinate for the first time cyclic enones with different substitution patterns and various functional groups in one flask, whereas previous methods for this transformation required several steps. Additionally, the utility of the method was demonstrated in a short synthesis of the core structure of the Aspidosperma alkaloid jerantinine E.