Organic syntheses via transition metal complexes.: 116.: Carbocyclic four-, five-, and six-membered rings by condensation of (alkyl,ethoxy)carbene complexes (M = W, Cr) with α,β-unsaturated tertiary acid amides

4-Amino-1-tungsta-1,3,5-hexatrienes (CO)(5)W=C(OEt)CH C(NR2)CH=CHPh (3E)-2 and (eyelohexan-4-on-1-yl)carbene tungsten complexes 6 were obtained by condensation of (etlioxy,methyl)carbene tungsten complex (OC)(5)W=C(OEt)CH3 la with alpha,beta-unsaturated tertiary acid amides PhCH=CHC(=O)NR2 7 in the presence of POCl3/Et3N and (COCl)(2)/Et3N, respectively. Compounds 2 underwent a pi-cyclization to zwitterionic eta(1)-cyclopentadiene complexes 3. Condensation of (prim-alkyl,ethoxy)carbene complexes (CO)(5)M=C(OEt)CH2R1 1 (M = W, Cr; R-1 = C-C7H7, n-Pr) with compounds 7 afforded (cyclobutenyl)carbene complexes 9.