PALLADIUM-CATALYZED SYNTHESES OF NATURALLY-OCCURRING ACETYLENIC THIOPHENS AND RELATED COMPOUNDS

Article abstract of DOI:10.1016/S0040-4020(01)96897-8

5-(3-buten-1-ynyl)-2,2'-bithienyl (1a), a natural product first isolated from Tagetes roots which shows nematicidal and photo-induced fungicidal activity, and 2-phenyl-5-(3-buten-1-ynyl) thiophen (1b) have been synthesized using two different methods.The first one (Method A) involves the palladium-catalyzed cross-coupling of vinyl bromide with the Grignard reagents derived from 5-ethynyl-2,2'-bithienyl (6a) and 2-ethynyl-5-phenylthiophen (6b).The second method (Method B) utilizes the coupling reaction of vinyl bromide with 6a and 6b, respectively, in the presence of a catalytic amount of (PPh3)4Pd and CuI.Such reaction, which was carried out under phase-transfer conditions employing BnEt3N(+)Cl(-) as phase transfer agent and 2.5N aq NaOH as base, has been also employed to prepare a large number of heterocyclic acetylene derivatives including some naturally-occuring compounds.The experimental conditions of Method B allow also the direct production of heterocyclic acetylene derivatives (1) starting from 1-alkynyltrimethylsilanes (5) and organic halides (2).