Miscellaneous Decomposition and Elimination Reactions

Fragmentation and elimination reactions that cannot be included in any of the above categories are reviewed briefly in this section. It has not proved possible to classify these processes, but like reactions are grouped together. The photochemistry of reaction intermediates has been reviewed. 

Carbon-oxygen bond heterolysis is responsible for the observed photolyses of 9-aryl-9-xanthenols ° and llH-benzo[b]fluoren-11-ol. - - Evidence for the formation of the 9-fluorenol radical cation as well as the 9-fluorenyl cation has been obtained from a laser flash photolysis study of 9-fluorenol. 1, l-Di-2-thienylethanol undergoes light-induced dehydration to give i,i-di-2-thienylethylene.Single electron transfer pathways, however, are implicated in the ring cleavage reactions of a,j8-epoxy ketones in the presence of allyltributyltin - or alkylamines. 

Studies of the mercury-photosensitised decomposition of 2-azetidinone and 4,4-dimethyl-2-azetidinone have been described the major products in the latter case were carbon monoxide, 2-methylpropene and 2,2-dimethylaziridine. Examples of photo-chemically induced N-dealkylation have again been reported. 

In particular, analogous photosolvolyses of the N-arylmethyladenines (103) afford adenine (104) and the substituted benzyl alcohols (105), - and carbon-nitrogen bond homolysis has 

Evidence for the formation of triplet benzoyl nitrene on irradiation of 1-benzyl-l,2,4-triazolio-4-benzoylamidate (109) in the presence of benzophenone or thioxanthone has been described. 

Fragmentation and elimination reactions that cannot be included in any of the above categories are briefly reviewed in this Section. 

N-methyl-9-alkoxyacridans is reversed on irradiation at 77 K. Products of irradiation of oxiranes are derived via a number of decomposition pathways. Both the carbonyl ylide (122) and the 

Oxygen-oxygen bond homolysis is the initial step in the photorearrangement of 9,10-dimethyl-9,10-dihydro-9,10-epidioxy- 

Photodealkylation of amines is a well-documented reaction -Dimethylamino- -nitrodiphenylethyne has been shown to undergo 

An unusual a,a-elimination of two phenyl groups is proposed on irradiation of the 1,1,1-triphenylalkane (129) in methanol and results in the formation of biphenyl (130) and the photoproducts (131) and (132) derived from the carbene (133) 

Various photoreactions arising by carbon-oxygen bond cleavage have been reported. Photoinduced single electron transfer-initiated cleavage of the benzylic ether protecting 

Single electron transfer-initiated N-demethylation of N-methylated alkaloids and N,N -dimethylanilines has been described, and a photoremovable a-methylphenacylamido protecting 

Photocyclization reactions accompanied by elimination of HCl and HBr have proved to be synthetically useful although in some cases details of the reaction mechanisms are not clear. 

Products arising by carbon-nitrogen bond homolysis have been obtained on irradiation of iV-benzyldiphenylamine, dimers of 2,4,5-triphenylimidazolyl, and A -alkyl-4-(carboalkoxy)pyridinyl radicals. The pyrazoline carbonyl ylides 

The major products, in order of decreasing amounts, of the photolysis k = 147 nm) of 1,1-dimethylcyclopropane have been shown to be isobutene, ethylene, hydrogen, buta-1,3-diene, 2-methylbuta-1,3-diene, propylene, allene, 

Transformations arising by photoinduced nitrogen-chlorine bond homolysis have again been observed. The Hofmann-Loffler-Freytag reaction of A-chloro-L-amino-acids, for example, affords 5-chlorinated intermediates which can be cyclized to L-prolines, and the yV-chloroamine (195) is converted on irradiation 

Intramolecular photoelimination of HCl, HBr, and HI, often initiated by carbon-halogen bond homolysis, has again been widely used in the synthesis of heterocycles and alkaloids. 6-Acetyl-l,2-dimethoxy-4//-5,6,6a,7-tetrahydrobenzo-[rf ]thieno[2,3-g]quinoline (197), for example, has been obtained in this way by irradiation of the bromothiophen (198). Analogous photocyclizations have been employed in the synthesis of ( + )-oliveroline, ( )-domesticine,  

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