Scalable Total Synthesis of Acremolactone B.

ABSTRACT

Acremolactone B is a pyridine-containing azaphilone-type polyketide with herbicidal activity. We developed an aza-6π electrocyclization-aromatization strategy to construct the tetrasubstituted pyridine ring and achieved the first total synthesis of this molecule on a gram scale. A bicyclic intermediate was expeditiously prepared by using [2 + 2] photocycloaddition and chemoselective Baeyer-Villiger oxidation, which was further elaborated to a densely substituted aza-triene. An electrocyclization-aromatization cascade was exploited to forge the tetracyclic core of the natural product, and the side chain was introduced through diastereoselective acylation and reduction.