PALLADIUM-MEDIATED INTRAMOLECULAR FORMATION OF A C-S BOND - APPLICATION TO THE SELECTIVE SYNTHESES OF 6-MEMBERED AND 7-MEMBERED SULFUR-CONTAINING HETEROCYCLES

Cyclopalladated complexes derived from benzylmethyl sulfide, o-iodo sulfides, or methyl-2-biphenyl sulfide react with alkynes to give stable organometallic compounds whereby the alkyne has inserted in the carbon-palladium bond. Activation of these complexes was effected by treatment with a silver salt, and resulting thermolysis led to a selective depalladation process, affording a series of both neutral and cationic 1H-2S-benzothiopyran derivatives. With dissymmetric alkynes this reaction displayed a high degree of regiocontrol. Under similar conditions, a new entry for the synthesis of derivatives of the rare family of dibenzo[bd]thiepins was acheived.