1,2 and 1,6 additions of lithium reagents to gamma-methylenepyran Fischer-type carbene complexes; Evolution of the 1,2 and 1,6 adducts to unsaturatedcarbene complexes indirectly stabilized by a heteroatom, and to pyranylidene carbene complexes

1,2 and 1,6 additions of lithium reagents to gamma-methylenepyran Fischer-t ype carbene complexes are described. The 1,2 adducts obtained from alkynyll ithium addition evolve by a 1,3 shift of the W(CO)(5) fragment to give alle nyltungsten carbonyl intermediates. Reaction with degassed water affords un saturated carbene complexes indirectly stabilized by a heleroatom. The 1,6 anionic addition products are quenched by H2O at low temperature to give al pha,delta-unsaturated carbene complexes. On warming, an evolution occurs le ading to new pyranylidene carbene complexes.