COPPER-CATALYZED REACTION OF TERMINAL ALKYNES WITH NITRONES - SELECTIVE SYNTHESIS OF 1-AZA-1-BUTEN-3-YNE AND 2-AZETIDINONE DERIVATIVES

Reaction of arylacetylenes with C,N-diarylnitrones using a catalyst system of CuI-dppe (dppe = 1,2-bis(diphenylphosphino)ethane) in the presence of potassium carbonate in DMF predominantly affords the corresponding 1,2,4-triaryl-1-aza- 1-buten-3-ynes in good yields. In contrast, the catalytic reaction using CuI in the presence of an excess amount of pyridine as the ligand gives 1,3,4-triaryl-2-azetidinones as the major products. The reaction with aliphatic terminal alkynes in place of arylacetylenes produces the latter products irrespective of the catalyst system used. Asymmetric induction is also observed in the reaction of phenylacetylene with alpha,N-diphenylnitrone to give 1,2,4-triphenyl-2-azetidinone in the presence of chiral bisoxazoline-type ligands.