FISCHER-TYPE CARBENE COMPLEXES IN ORGANIC -SYNTHESIS

The addition reaction of organolithium or Grignard reagents to silyl-s ubstituted Fischer-type carbene complex gives either E- or (Z)-vinylsi lanes with high selectivities depending on the reaction conditions. A new type of propargyl metallic species is generated by the addition re action of alkynyllithiums with Fischer-type carbene complexes. These s pecies act as regiochemically well-behaved propargyl metallic species and react with various electrophiles to give five-membered heterocycli c compounds. This reaction was applied to a concise enantioselective t otal synthesis of (-)-PI-091. Variable temperature NMR studies of the reaction of the propargyl tungsten species with electrophiles revealed that 1,2-migration of pentacarbonyltungsten occurs to generate a viny l metallic species. Highly efficient method was developed for the prep aration of a variety of synthetically useful, fully substituted five-m embered heterocyclic compounds by the iodine-oxidation of the intermed iates produced from Fischer-type carbene complexes, alkynes, and vario us carbon electrophiles.