Scandium-catalyzed carbon-carbon bond formations using alpha-organosulfanyl and organoselanyl-alpha-fluoroacetic acid derivatives.

The scandium-catalyzed reactions of alpha-organosulfanyl and organoselanyl-alpha-fluoroacetates 1-2, acetamides 3-4 and acetonitrile 5 with soft nucleophiles proceeded to give the products 6a-b, 7a-c, 8a-c, 9a-e in good to high yields. We also successfully performed the scandium-catalyzed intramolecular cyclization reactions and obtained the unique 5-methylene-2-oxotetrahydropyrans 16-17.

A novel 3,4-bis(sulfenyl)- or 4-selenenyl-3-sulfenylpenta-2,4-dienylation of aldehydes using 4-ethoxy-1,2-bis(sulfenyl)- or 1-Selenenyl-2-sulfenyl-buta-1,3-dienyl lithiums.

3,4-Dichalcogenopenta-2,4-dienylation of aldehydes proceeded in good to high yields using 4-ethoxy-1-(benzenesulfenyl)-2-(methanesulfenyl)- (5), 4-ethoxy-1,2-bis(benzenesulfenyl)but-1,3-diene (6), and 1-selenenyl derivatives 7 and 8. This novel four-carbon homologation could be applied to a synthesis of 3,4,7,8-tetrakis(benzenesulfenyl)-10,10-dimethylundeca-2,4,6,8-tetraenal (20).