Condensation of propargylic alcohols with 1,3-dicarbonyl compounds and 4-hydroxycoumarins in ionic liquids (ILs)

Propargylic alcohols are activated toward 1,3-diketones by Lewis or Brønsted acidic ionic liquids (ILs) without an added catalyst, but significantly better conversions are achieved with metallic triflates [in particular Sc(OTf)3 and Ln(OTf)3] and bismuth nitrate in imidazolium ILs. The scope of this condensation reaction was investigated with a variety of propargylic alcohols and a host of acyclic and cyclic dicarbonyl compounds. Concomitant cycloisomerization leading to tetrasubstituted furans was observed with the propargylic alcohols 1b and 1c in reaction with 1,3-diketone 2b and the β-ketoester 2c. With propargylic alcohol 1c, propargylation, cycloisomerization, or dienone formation were observed, depending on the structure of the 1,3-dicarbonyl compound. The [BMIM][PF6]/Bi(NO3)3·5H2O system proved efficient for propargylation, vinylation, and alkylation of 4-hydroxycoumarins. The recycling and reuse of the IL are added advantages of this method.