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 compl ex (OC)(5)W=C(OEt)C drop CPh (1a) gave cross-conjugated carbiminium carbony lmetalates 3, which isomerized to pyrilium carbonylmetalates 4 in 62-90% yi elds. The isomerization involves a skeletal rearrangement of a cross-conjug ated carbiminium carbonyltungstate to a (conjugated) 1-tungsta-1,3,5-hexatr iene by formation of (4-aminocyclobutenyl)carbene complexes as intermediate s. Dinuclear carbene derivatives of dihydrobarrelene 5 were derived from py rilium carbonylmetalates 4 by [4 + 2] cycloaddition to (1-alkynyl)carbene c omplexes 1 in 63-73% yields. Reactions of cyclic 1,3-diketones 7 with (1-al kynyl)carbene complexes 1 gave pyrilium carbonylmetalates 10 and 11 in 35-9 1%. (C) 2000 Elsevier Science Ltd. All rights reserved.