Total Synthesis of (+)‐Carbonolide B.

The macrolide (+)-carbonolide B, the aglycon of the antibiotic carbomycin B, was synthesized via a convergent sequence. A key step of the approach is the union of aldehyde 6 with stannane 7 in the presence of MgBr 2 -OEt 2 as Lewis acid to afford the C 1 -C 9 fragment 26. This chelation-controlled process uses resident stereochemistry at C 4 to control stereochemistry at C 5 and C 6 . Elaboration of this fragment at both ends and incorporation of a C 11 -C 15 fragment (hydroxy enal 4) via esterification and intramolecular Emmons reaction was used to complete the synthesis