Synthesis of the C(7)–C(22) Sector of (+)-Acutiphycin
via O‑Directed Double Free Radical Alkyne Hydrostannation with
Ph<sub>3</sub>SnH/Et<sub>3</sub>B, Double I–Sn Exchange, and
Double Stille Coupling
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Abstract
Herein a new double
O-directed free radical hydrostannation reaction
is reported on the structurally complex dialkyldiyne <b>11</b>. 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 <b>10</b> were concurrently constructed with high stereocontrol using Ph<sub>3</sub>SnH/Et<sub>3</sub>B/O<sub>2</sub>. Distannane <b>10</b> was thereafter elaborated into the bis-vinyl iodide <b>9</b> via O-silylation and double I–Sn exchange; double Stille
coupling of <b>9</b>, O-desilylation, and oxidation thereafter
furnished <b>8</b>