Site selectivity in attack by carbenes on substituted benzenes. 5-Diazomethyl-1,4-diphenyl-1,2,3-triazole

Abstract

5-Diazomethyl-l,4-diphenyl-l,2,3-triazole (I) reacts with monosubstituted benzenes at 40-50°to give 72-90% yields of mixtures of 7-(l,4-diphenyltriazol-5-yl)tropilidenes in which the predominant isomer has the substituent in the 3 position (CH3 or F) or the 2 position (CH3O). The relative reactivities of monosubstituted benzenes toward the carbene from I were determined by competition experiments; they could be correlated by a Hammett equation in ap with = -1.0, corresponding to an electrophilic species with a selectivity more closely resembling that of carboethoxynitrene than carboethoxycarbene. 5-(a-Diazobenzyl)-l,4-diphenyltriazole thermolyzed more slowly than the diazomethyl analog, but still showed first-order kinetics with a rate constant independent of solvent in the absence of a proton source. It did not form addition or insertion products, but gave a mixture consisting principally of the symmetrical tetrasubstituted ethylene, the corresponding ethane, and 5benzoyl-1,4-diphenyltriazole. These products, the result of dimerization, abstraction of hydrogen, and reaction with O2, imply the intermediacy of a carbene in the triplet state.

Persistent Triplet Carbenes

“…These products, the result of abstraction of hydrogen, dimerization, and reaction with O 2 , are those typical of triplet carbenes, and products attributable to singlet carbenes such as ketazine were evidently not formed in significant quantities. 193 Spectroscopic studies and further modification of this type of carbene are desired.…”

Reactions in the conjugated ‘ene–ene–yne’ manifold: five-membered ring fragmentation and ring formation via coarctate/pseudocoarctate mechanisms

“…The resultant cyanoimine intermediates underwent further rearrangement to give a mixture of triazoles 21a-e and regioisomeric triazines 22a-e. 30,31 Changing from a nitrene to carbene functionality in the a position does not give rise to any ring opened products, but rather resulted in solvent incorporation at the carbene. [32][33][34] Even in cases where there was no carbene trap (i.e., hexafluorobenzene as the solvent) no products derived from ring opening were detected.…”

Dehydrogenation of Hydrazones

“…It is assumed that the formation of the azine occurs via radical dimerization and does not involve a diazo interme diate (57). It is assumed that the formation of the azine occurs via radical dimerization and does not involve a diazo interme diate (57).…”

“…It is assumed that the formation of the azine occurs via radical dimerization and does not involve a diazo interme diate (57). The yield is far superior to the magnanese(IV) oxide or the mercury(II) oxide reaction in the synthesis of 5-diazomethyl-l,4diphenyl-l,2,3-triazole (37 -+ 38) (57). The yield is far superior to the magnanese(IV) oxide or the mercury(II) oxide reaction in the synthesis of 5-diazomethyl-l,4diphenyl-l,2,3-triazole (37 -+ 38) (57).…”

“…H3C-COOH/-N2 lead(IV) acetate dehydrogenation of 17/?-acetoxy-5a-androstan-3-one hydrazone (30) can be explained along these lines(50). 3/?-Hydroxy-24-androsten-7-one hydrazone reacts similarly(57).…”