Organic syntheses via transition metal complexes, LXXXVIII: 1-Metalla-1,3,5,7-octatetraenes from (1-alkynyl) carbene complexes of chromium and tungsten via [6-(1-alkenyl)]pyranylidene complexes

Article abstract of DOI:10.1016/S0022-328X(97)00051-X

[6-(1-Ethenyl)]pyran-2-ylidene complexes 4a,b and [6-(1-butadienyl)]pyran-2-ylidene complexes 6a,b are obtained as major products together with the corresponding regioisomeric pyranylidene complexes 5a,b and 7a,b respectively as minor products by base-induced condensation of (1-alkynyl)carbene complexes (CO)₅M=C(OEt)-C≡CPh 1a,b (M = Cr, W) with trans-6-phenyl-5-hexene-2,4-dione (2b) and trans,trans-8-phenyl-octa-5,7-diene-2,4-dione (2c) in moderate yields. X-ray data of the isomeric tungsten complexes 4b and 5b [C₂₆H₁₆O₇W, blue (red), triclinic (monoclinic), space group P1 (P2₁/c), Z = 2 (4)] and the pyranylidene compound 6b [C₂₈H₁₈O₇W, triclinic, space group P1, Z = 2] are reported. Amination of compound 4b with dimethylamine affords 1-metalla-1,3,5,7-octatetraenes (Z,Z,E)-9A and (Z,Z,E)-9B (2:1) in 89% total yield.