ORGANIC SYNTHESES VIA TRANSITION-METAL COMPLEXES, XCI - DIHYDROPYRIDINYL CARBENE COMPLEXES BY [4-IMINE OR ARYL-IMINE TO (1-ALKYNYL)CARBENE COMPLEXES OF CHROMIUM AND TUNGSTEN(2]ANNULATION OF ALKENYL)

Reaction of (1-alkynyl)carbene complexes (CO)(5)M=C(OEt)C=CPh 1a,b (M = W, Cr) with alkenyl imine PhCH=CH-CH=N(i-Pr) 2 affords dihydropyridi nyl carbene complexes 3 (by an overall 4 + 2 cycloaddition) and zwitte rionic 1-azonia-5H-cycloheplatrien-3-yl carbonylmetalates 4 (by an ove rall 4 + 3 cycloaddition). The product ratio 3:4 is strongly influence d by steric demand of the metal unit as well as of the substrate. Thus , compounds 3 (generated by 4-addition of the imino function to the C= C bond of la) are major products in case of M = W, whilst compounds 4 (generated by 2-addition of the imino function to Ib) are major produc ts in case of M = Cr. Reaction of sterically congested imines, e.g. ph enanthrene-9-carboximine 5, affords [4 + 2] cycloadducts, e.g. 6a,b as the only detectable products. Compounds 6 undergo hydrolysis on chrom atography on silica gel and give a carbaldehyde 7. Crystal structures are reported of compounds 3a and 6a. (C) 1997 Elsevier Science S.A.