Tandem Cyclization of Enynes Containing a Thioether or Ether Linkage via Ruthenium Allenylidene and Vinylidene Complexes

Abstract

The two aromatic S-enynes HC≡CCH(OH)(C6H4)SCH2C(R)═CH2 (1a, R = Me; 1b, R = H) containing olefinic groups with and without an internal methyl substitutent and the O-enyne HC≡CCH(OH)CMe2CH2OCH2C(Me)═CH2 (1c) also with an internal methyl substituent on the olefinic group but with no aromatic group have been prepared. In the [Ru]Cl-induced ([Ru] = Cp(PPh)3Ru) reactions of 1a,c, the presence of the methyl group promotes cyclization reactions and their tandem cyclizations are further induced by MeOH. The reaction of 1a in CH2Cl2 gives the three products 2a–4a. Complex 2a, with a seven-membered thio ring bonded at Cβ of the vinylidene ligand, is formed via a C–C bond formation between two unsaturated groups in moderate yield. Complex 3a is formed via migration of PPh3 from the metal onto the terminal carbon of the alkynyl group followed by coordination of the S atom. The carbene complex 4a is formed by S addition to the internal carbon of the alkynyl group accompanied by migration of the allylic group from sulf...