Intramolecular Photoacylation of Carbamates and Carbonates¹

Enamide photochemistry. Stereochemistry of photocyclization of 1-ethylidene and 1-benzylidene 2-benzoyltetrahydroisoquinolines

“…The isopropylidene enamide 1 was synthesized to determine whether the two methyl groups would cause sufficient steric interference in the photocyclization to $low a [1,3]-acyl shift to become competitive.6 Additionally, if the photocyclization did occur, the 13,13-gem-dimethyl group should allow observation of thie low-field 13a hydrogen as a singlet and the second low-field resonance as the C-6 equatorial h y d r~g e n .~ The enamide 1 was readily synthesized from 3,4-methylenedioxybenzoyl chloride and 3,4-dihydro-l-isopropyl-6,7-dimethoxyisoquinoline. The acid chlorides give better yields in cases where the 1 substituent is other than methylene.s The NMR spectrum of 1 showed that the C-3-C-4 ethylene bridge no longer appeared as two triplets as in the equivalent 1-methylene enamide,' but that the l-isopropylidene group forced the benzoyl group into a conformation where it was within 1.7-1.8 A of the axial C-4 hydrogen.…”

“…The photocyclization reactions of enamides have been extensively studied over the last few years and have proven to be valuable in building polycyclic ring systems from easily accessible precurs0rs.l This photocyclization is generally viewed as proceeding through the aza analogue of hexatriene-cyclohexadiene photocyclization to form an intermediate which undergoes a [1,5]-hydrogen shift.1a!2 The [1,5]hydride shift, although postulated, has never been demonstrated. Additionally, the reaction has been reported to be stereospecific," as well as nonstereo~pecific.~ The reason for the stereospecificity may well be that virtually all of the reported cyclizatiions have utilized an ardmatic double bond and an olefinic bond constrained in a ring.…”

6H-Dibenzo[b,d]pyrans. I. Synthesis

“…The intramolecular. condensation of 2'-nitrobiphenyl-2-carboxylic acid 1 (15), the photoacylation of ethyl 2-biphenylyl carbonate 2 (16), and the Baeyer-Villiger oxidation of 9-fluorenones (17,18) offer interesting and novel approaches. most conveniently prepared by the condensation of the appropriate 2-bromobenzoic acid with resorcinol or a 2-substituted resorcinol in the manner described by Hurtley (19).…”

Studies on enamides. Part-7: a novel photochemical reaction pathway of N-aroyl-N-1-cyclohexenylanilines

“…It is known [10][11][12] that for enamide photocyclisation reaction the involvement of the lone pair of the nitrogen atom is necessary. In the present instance, such participation of the lone pair of the nitrogen atom is difficult as the same is experiencing a conjugative effect of the phenyl group attached to the nitrogen atom.…”