Concise syntheses of (+)-macrosphelides A and B: Studies on the macro-ring closure strategy

Highly concise syntheses of (+)-macrosphelides A and B were accomplished in this study. The key feature of our synthetic route involved the direct three-carbon homologation of the readily available Weinreb amide 6 by the addition of a trans-vinylogous ester anion equivalent and facile construction of the 16-membered macrolide skeleton of macrosphelides via an intramolecular nitrile oxide-olefin cycloaddition. The syntheses of macrosphelides A and B were completed with a 30 and 20% overall yield, respectively. This paper describes the details of our syntheses.