Photoreduction and Photoaddition of N-Acetyldiphenylmethyleneamine in Alkylbenzenes

Abstract

Irradiation of N-acetyldiphenylmethyleneamine (II) in toluene solution gave N-(1,1,2-triphenylethyl)acetamide and N-(1,1-diphenylmethyl)acetamide in 11% and 4.4% yields, respectively. The former is an addition product of toluene to the C=N bond of imine II, and the latter a hydrogenation product of II. The same kind of addition and hydrogenation products as those in toluene were obtained on irradiation of imine II in ethylbenzene, cumene, o-, m-, and p-xylene, mesitylene, p-methoxytoluene, and p-cyanotoluene, respectively. Two kinds of competitive reaction processes are proposed from the results of the substituent effects for the phenyl ring of toluene, the effect of the additives such as sensitizers and quenchers, and the dependence of the photoreaction yields on the concentration of the additive. The photoreaction proceeds not only by the “chemical sensitization” mechanism derived from the ketyl radical of benzophenone, a hydrolyzed product of II, but also by the mechanism through the excited state of II itself.

Photochemistry of the carbon-nitrogen double bond

“…[112][113][114][115][116][117] Similar results were reported by Fraser-Reid and co-workers with related com-…”

“…The mechanism proposed to account for these observations involves excitation of the ketimine followed by intersystem crossing and hydrogen atom abstraction from the solvent by the triplet state. [112][113][114][115][116][117] Further support for the involvement of the triplet state in these systems was obtained by studying the photochemistry of several o-alkyl aromatic ¡mines (56).115-117 Irradiation of 56 was reported to result in an isomerization to an enamide derivative (57) by a path similar to that observed with the related o-alkylbenzophenone system.136,137 On the basis of these observations it would appear as though the mechanism for the reduction of { V-ch2d /V-acylimines is quite different from that followed by /V-alkylimines. This difference is undoubtedly related to the presence of the carbonyl group in the /V-acylimine system.…”

Selective and Functional-Group-Tolerant Photoalkylation of Imines by Energy-Transfer Photocatalysis

“…Prior reports of sp 3 C–H aminoalkylation are far more restrictive in scope and efficiency. Toshima’s seminal work did successfully demonstrate ketone-like photoalkylation of imines over 50 years ago, but only on one imine ( N -acetyl benzophenone imine) and with exclusively allylic and benzylic hydrocarbons in low yields (up to 40% yield; Scheme A). Later, Kisch et al reported photoalkylation of N -phenylimines in yields up to 49% .…”