Total syntheses of the antimicrobial tricyclic 16-membered macrolides, (+)-tubelactomicin B, (+)-tubelactomicin D, and (+)-tubelactomicin E, have been accomplished for the first time with common synthetic approaches. These total syntheses established the relative and absolute configurations of the three tubelactomicins, for which planar structures had solely been reported. The totalsynthesis of (+)-tubelactomicin
A formalsynthesis of the antimicrobial tricyclic macrolides, tubelactomicins A and E, featured by a transannular Diels–Alder (TADA) approach, has been explored. The key issue for the transannular cyclization was the synthesis of a 24-membered macrolactone equipped with all the requisite functionalities, which has been achieved using an intramolecular Hiyama cross-coupling strategy. The Hiyama coupling
[reaction: see text]. Starting from diethyl (R)-malate, synthesis of the lower-half segment of (+)-tubelactomicin A, a 16-membered macrolide antibiotic, has been achieved. The synthesis involved the highly endo- and pi-facial selective intramolecular Diels-Alder reaction achieved using a trisubstituted methacrolein derivative tethering a 10-carbon dienyne unit at the beta-carbon, which in turn was