Synthesis of the A-B subunit of angelmicin B.

An efficient synthesis of the tricyclic A−B subunit 2 of angelmicin B is described. A formal three-component coupling of aldehydes 4 and 6 with γ-silylallylborane 7 was employed to assemble the tetrahydrofuranyl core of 2, a strategy highlighted by the stereoselective [3 + 2] annulation of allylsilanes 5a/5b with aldehyde 4. The efficiency of the [3 + 2] annulation was greatly improved by using the allylic benzhydryldimethylsilane 5b compared to the allylic phenyldimethylsilane 5a.