PALLADIUM(0)-CATALYZED THIOBORATION OF TERMINAL ALKYNES WITH 9-(ALKYLTHIO)-9-BORABICYCLO[3.3.1]NONANE DERIVATIVES - STEREOSELECTIVE SYNTHESIS OF VINYL SULFIDES VIA THE THIOBORATION CROSS-COUPLING SEQUENCE

The addition of 9-(alkylthio)-9-borabicyclo[3.3.1]nonanes(9-(RS)-9-BBN) 1 to terminal alkynes was catalyzed by Pd(PPh3)4 (3 mol %) to produce 9-[(Z)-2-(alkylthio)-1-alkenyl]-9-BBN derivatives 2 in high yields. The reactions were highly regio- and stereoselective, and their conditions were sufficiently mild that a variety of functionalized alkenylboranes 2 with defined stereochemistry were readily synthesized. The boranes 2 exhibited exceptionally high reactivity on protonolysis with methanol to produce the Markovnikov adducts of thiols to 1-alkynes, 2-(alkylthio)-1-alkenes 3. The synthetic utility of the present reaction was demonstrated by the regio- and stereoselective one-pot synthesis of alkenyl sulfides 7 via the palladium-catalyzed thioboration-cross-coupling sequence.