Phenol Formation from the Reaction of Amino-Stabilized Alkenyl Fischer Carbene Complexes

Article abstract of DOI:10.1021/jo00119a039

The first examples of phenol formation from the reactions of amino-stabilized α,β-unsaturated Fischer carbene complexes with alkynes are reported.A series of four dimethylamino complexes <(CO)5Cr=C(NMe2)R; 19, R = cyclohexenyl; 26, R = trans-propenyl; 27, R = trans-styryl; 30, R = isopropenyl> were examined with both internal and external alkynes.Their reactions with internal alkynes typically produced low yields of complex mixtures of products and were not synthetically useful.In contrast, their reactions with terminal alkynes were remarkably different giving good yields of 4-(dimethylamino)phenols, and in the presence of a trapping agent, good yields of the arene chromium tricarbonyl complexes of the protected 4-(dimethylamino)phenols.The selectivity for phenol formation was found to be greatest for reactions performed in noncoordinating solvents and at higher concentrations.In contrast, and as expected, the reaction of the aryl complex 45 <(CO)5Cr=C(NMe2)Ph> with 1-pentyne did not produce any six-membered ring product in DMF, THF, or benzene.An interesting solvent dependence was observed for this reaction where lactam 49 was the exclusive product in benzene and the indanone 46 was the exclusive product in DMF.