Synthesis of the C(7)–C(22) Sector of (+)-Acutiphycin via O-Directed Double Free Radical Alkyne Hydrostannation with Ph₃SnH/Et₃B, Double I–Sn Exchange, and Double Stille Coupling

Abstract

Herein a new double O-directed free radical hydrostannation reaction is reported on the structurally complex dialkyldiyne 11. Through our use of a conformation-restraining acetal to help prevent stereocenter-compromising 1,5-H-atom abstraction reactions by vinyl radical intermediates, the two vinylstannanes of 10 were concurrently constructed with high stereocontrol using Ph3SnH/Et3B/O2. Distannane 10 was thereafter elaborated into the bis-vinyl iodide 9 via O-silylation and double I-Sn exchange; double Stille coupling of 9, O-desilylation, and oxidation thereafter furnished 8.