Experimental Studies on the Selective β‑C–H Halogenation of Enones

Here
we describe the realization of a one-pot protocol for the
β-C–H halogenation of cyclic enones via umpolung of the
β-carbon. The developed method includes hydrazone formation
and selective β-halogenation (bromination, chlorination) with N-bromosuccinimide and Palau’chlor (2-chloro-1,3-bis­(methoxycarbonyl)­guanidine)
followed by hydrolysis of the hydrazone moiety. Using the optimized
conditions, we were able to effectively β-brominate and β-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.