ORGANIC SYNTHESES VIA TRANSITION-METAL COMPLEXES .72. (2-(ACYLOXY)ETHENYL)CARBENE COMPLEXES BY MICHAEL ADDITION OF CARBOXYLIC-ACIDS TO ALKYNYLCARBENE COMPLEXES (M=CR, W) - (2-(ACYLOXY)ETHENYL)KETENE IMINES BY LIGAND DISENGAGEMENT WITH ISOCYANIDE

(2-(Acyloxy)ethenyl)carbene complexes (CO)(5)M=C(OEt)-CH=C(OCOR)Ph [(Z)-5] (M = Cr, W; R = Ph, p-Me(2)NC(6)H(4), CH3, cC(7)H(7)CH(2), PhCH=CPh, Me(2)C=CH, 1,4-C6H4) are obtained by the addition of carboxylic acids R-CO2H (4) to alkynylcarbene complexes (CO)(5)M=C(OEt)-C=CPh (1) (M = Cr, W) in the presence of Et(3)N at 20 degrees C in 71-78% isolated yields. The reaction is regio- and stereochemically uniform. (Z)-5g (R=PhCH=CPh), C31H22O8W, was characterized by X-ray diffraction. It crystallizes in space group Pi with cell parameters a 10.381(6) Angstrom, b 11.444(6) Angstrom, c 13.509(7) Angstrom, alpha = 107.84(4)degrees, beta = 91.54(4)degrees, gamma = 108.49(4)degrees, Z = 2, R(1) = 0.0354, and wR(2) = 0.0811. Ligand disengagement from (Z)-5 with tert-butyl isocyanide (8b) at 20 degrees C results in the formation of [2-(acyloxy)ethenyl]ketene imines t-BuN=C=C(OEt)-CH=C(OCOR)Ph [(Z)-11] (> 95% yields).