Organic Syntheses via Transition Metal Complexes. Part 103: Pyrylium Carbonylmetalates and Related Compounds Derived from (1-Alkynyl)carbene Complexes (M=Cr, W)

Cyclic tertiary enaminones 2a-e and (2-phenylalkynyl)carbene tungsten complex (OC)5W=C(OEt)CCPh (1a) gave cross-conjugated carbiminium carbonylmetalates 3, which isomerized to pyrilium carbonylmetalates 4 in 62–90% yields. The isomerization involves a skeletal rearrangement of a cross-conjugated carbiminium carbonyltungstate to a (conjugated) 1-tungsta-1,3,5-hexatriene by formation of (4-aminocyclobutenyl)carbene complexes as intermediates. Dinuclear carbene derivatives of dihydrobarrelene 5 were derived from pyrilium carbonylmetalates 4 by [4+2] cycloaddition to (1-alkynyl)carbene complexes 1 in 63–73% yields. Reactions of cyclic 1,3-diketones 7 with (1-alkynyl)carbene complexes 1 gave pyrilium carbonylmetalates 10 and 11 in 35–91%.