C‐Nitroso compounds. Part XXX. The mechanism of photolysis of chloro nitroso compounds; irradiation of 2‐chloro‐2‐nitrosoadamantane in methanol

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Abstract
The photolysis of gem‐chloronitrosoalkanes 1 in methanol has been studied with the model compound 2‐chloro‐2‐nitrosoadamantane (AdClNO) 1a. The mechanism is outlined in Scheme 1, and involves initial C‐NO bond cleavage. The generated chloroalkyl radicals 2 are captured by unchanged starting material giving the key intermediate, a 1,1′‐dichloro nitroxide 3. Although this process is probably reversible in inert solvents, nitroxide 3 is irreversibly removed in alcohols by conversion into a N‐(1‐chloroalkyl)nitrone 4, which is solvolysed to an equimolar mixture of an acetal and an oxime. During photolysis no ESR signals are observed. Nevertheless, the transient existence of chloro nitroxides 3 is supported by the detection of di‐sec‐alkylnitroxides 5, which are formed when a photolyzed solution of a chloro nitroso compound 1 is treated with tri‐n‐butylstannane (reaction [7]). The mechanism is further supported by photolysis of AdClNO in the presence of nitrosobenzene in aprotic solvents and isolation of the relatively stable hydrochloride of the nitrone: phenyladamantylideneamine oxide 6a.