Synthesis of a Small-Molecule Library with Skeletal Diversity from Hemslecin A via the Reaction-Discovery Strategy

An efficient reaction
tool box was developed for the synthesis
of skeletally diverse and stereochemically complex templates for a
small-molecule library based on the common synthon Q,
which was prepared from hemslecin A in four steps. The reaction tool
box comprises three acid-promoted rearrangements: semipinacol, Wagner–Meerwein,
and cyclopropylmethyl cation rearrangements. More importantly, a Mn-mediated
C–H oxidation was developed to achieve a high level of complexity,
which provides a new entry for C–H functionalization of inert
angular methyl groups in the chemistry of triterpenes. Our reaction-discovery
strategy based on hemslecin A provides a basis for the inherent chemistry
of triterpenes and could be applied for the further transformation
of triterpenes.