Ethenyl carbenes

Y. [(2-Phosphanyl)ethenyl]carbene Complexes by Addition of Secondary Phosphanes.214... 

Alkoxy(l-alkynyl)carbene complexes also are obtained by condensation of (l-ethoxy)methylcarbene complexes with bulky acyl chlorides as side products (10-12% yield) together with [(2-acyloxy)ethenyl]carbene complexes (50-78% yield),36 e.g., (CO)5M=C(OEt)—CH3 + 3 RCOC1 + 3 Et3N — (CO)5M=C(OEt) - CR (M = Cr, W R = r-Bu, c-Pr). 

Aminomethylenation of [2-(AT/-amino)ethenyI]carbene complexes affords alkoxy(l-alkynyl)carbene complexes (22-30% yield) by /3-elimination, together with [2-amino-l-(iminoacyl)ethenyl]carbene complexes (61-83% yield),37 e.g., (CO)5M=C(OEt)-CH = CPh(NHPh) + HCONR2 + POCl3/Et3N - (CO)5M = C(OEt) — C=CPh (M = Cr, W R = pyrrolidine, morpholine). 

I. [2-(Acylamino)ethenyl]carbene Complexes by N-Acylation of (NH-Enamino)carbene Complexes... 

Alkyloxy)ethenyl]carbene complexes (CO)5M=C(OEt) —CH=C (O-alkyl)R1151 (M = Cr, W) are accessible by several methods, including (i) the condensation of a methylcarbene complex (CO)5M=C(OEt)CH3 with dimethylformamide and other nonenolizable acid amides R1 — CONR2,174 (ii) the condensation of a methylcarbene complex (CO)5M =... 

The [(2-alkoxy)ethenyl]carbene complexes are obtained as E/Z mixtures, in which the (E)-stereoisomers predominate. Other carbene complexes, in which carbohydrates are bonded directly to the metal center178 or to the carbene carbon atom,179180 are also known. 

Alkoxy)ethenyl]carbene complexes easily undergo insertion of an isocyanide into the M = C bond.3qn9 Reaction of cyclohexyl isocyanide with [2-(alkoxy)ethenyl]carbene complex ( )-154 yields a 4,5-dihydropyr-rolylidene complex 160 (Scheme 66),169 in agreement with earlier observations of similar reactions of related carbene complexes.17415186... 

Photolysis of [(Z)-2-(acyloxy)ethenyl]carbene complexes (= 4-acyloxy-1-chroma-l,3-dienes) (CO)sCr=C(OEt)-CH=C(OCOR1)R (Z)-169 (R = C6H5, t-Bu, c-Pr R1 = C6H5, c-Pr, c-C7H7CH2, f-Bu, Me2C=CH) with UV light of >300 nm affords 2-butene 1,4-diones R CO —C(OEt)=CH — COR (E)-170 (60-68%) by a novel metal-mediated acyl migration. Compounds (Z)-171 and furans 172 are formed as minor products (Scheme 72).4g... 

Scheme 72. Butene 1,4-diones by photolysis of [2-(acyloxy)ethenyl]carbene complexes.

Alkoxy pyrrholes, synthesis, 203 [2-(Alkyloxy)ethenyl]carbene complexes,... 

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