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

Abstract

2-(Acyloxy)ethenyl)carbene complexes (CO)5M=C(OEt)-CH=C(OCOR)Ph [(Z)-5] (M = Cr, W; R = Ph, p-Me2NC6H4, CH3) c-C7H7CH2, PhCH=CPh, Me2C=CH, 1,4-C6H4) are obtained by the addition of carboxylic acids R-C02H (4) to alkynylcarbene complexes (CO)sM=C-(OEt)-C=CPh (1) (M = Cr, W) in the presence of Et3N at 20 °C in 71-78% isolated yields. The reaction is regio-and stereochemically uniform. (Z)-5g (R = PhCH=CPh), C3iH220eW, was characterized by X-ray diffraction. It crystallizes in space group PI with cell parameters a = 10.381(6) Á, b = 11.444(6) Á, c = 13.509(7) Á, a = 107.84(4)°, ß = 91.54(4)°, = 108.49-(4)°, Z = 2, Ri = 0.0354, and wR2 = 0.0811. Ligand disengagement from (Z)-5 with tertbutyl isocyanide (8b) at 20 °C results in the formation of [2-(acyloxy)ethenyl]ketene imines i-BuN=C=C(OEt)-CH=C(OCOR)Ph [(Z)-ll] (>95% yields).Alkenylcarbene complexes (CO)sM=C-C=C of chromium and tungsten have gained much interest recently as C3 building blocks for the synthesis of car-bocyclic2 and heterocyclic3 rings. Though this class of compounds has been known since 1967,4 systematic studies have been initiated only recently. Complexes (CO)sM=C-C=C(OR1) of types A and B deserve particular attention due to their structural relationship to ß-keto ester equivalents of the enol ether (R1 = alkyl) and enol ester type (R1 = acyl), respectively (Chart 1). Enol Ethers 3Complexes (CO)5M=C-C=C[0(alkyl)] (M = Cr, W) of the enol ether type are accessible by several methods (Scheme 1): (a) by the condensation of methylcarbene complexes (CO)5M=C(OEt)CH3 with dimethylformamide or other nonenolizable acid amides R1-CONR2 (eq l),5

Addition of protic nucleophiles to alkynyl methoxy carbene ligands in diiron complexes

“…The δ(C β -H) resonance at 7.05-7.48 ppm suggests a Z configuration for the double bond, and this is also the stereochemistry usually observed for this class of reactions [1,10]…”

Fischer Carbene Complexes as Chemical Multitalents: The Incredible Range of Products from Carbenepentacarbonylmetalα,β-Unsaturated Complexes

“…[59] Benzoic acid (118) reacts uniformly with 48 (M Cr) in the presence of triethylamine to form the Z-isomer 119 in 76 % yield.…”

Fischer-Carbenkomplexe als chemische Multitalente: die unglaubliche Produktpalette ausα,β-ungesättigten Carbenpentacarbonylmetall-Komplexen

“…Auch die Michael-Addition von Carbonsäuren an Alkinylcarben-Komplexe gelingt glatt. [59] Benzoesäure 118 reagiert in Gegenwart von Triethylamin mit 48 (M Cr) einheitlich zum (Z)-Isomer 119 (76 % Ausbeute).…”