Cyclohexane photochemical aromatization

Aromatic compounds can participate in both [2+2] and [4+2] photocycloaddition reactions with uracil derivatives to give either benzocyclobutane or ethenoquinazoline (barrelene) derivatives, which can then undergo a number of subsequent photochemical reactions. The products obtained are dependent upon the reaction conditions, and thus the photocycloaddition reaction between naphthalenes 470 and l,3-dimethyl-5-fluorouracil 471 in cyclohexane gave 4a-fluoro-5,10-ethenobenzo[/]quinazolines 472 as products as a result of a [4+2] photocycloaddition (photo-Diels-Alder) reaction <2002TL3113, 2003H(61)377>. 

An interesting photochemical formation of different 1,4-dihydro-1,3,5-triazines (168-171) was demonstrated by Kobayashi et al.261 who irradiated substituted 1,3,5-triazines (167) of low aromaticity in pentane or cyclohexane, utilizing compounds with two different fluoroalkyl groups on the triazine ring. Two or three distinct products were isolated, the ratio of these dihydro compounds depending on the nature of both substituents and the solvent (which also serves as a reagent) [Eq. (82)].267... 

Photochemical cyclohexane carbonylation was found to be co-catalyzed by d transition metal carbonyls, and aromatic ketones and aldehydes [47], The following mechanism has been suggested for this reaction. 

Boron.—Reactions of boron trichloride with aromatic amines may proceed by formation of the Cl3B,NH2R adduct and then by hydrogen chloride elimination to give ClaB=NHR en route to the ultimate product (CIB—NR),. The mechanism of these reactions has been probed by isolation and characterization of intermediates, and stoicheiometric and kinetic studies -the kinetics can be followed by monitoring the evolution of hydrogen chloride. Photochemical reaction of triethylboron with iodine in cyclohexane takes place by a free-radical mechanism, indicated by the determined rate law. ... 

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