Acrylates, 3- -, cyclization pathways

Irradiation of 1-methyl-2-nitrocyclohexene 200 in benzene in the presence of methyl acrylate showed a dual pathway to give both isoxazoline 201 (54%) and the C-nitroso dimer 202 (22%)118 (equation 96). The isoxazoline 201 arose from an excited-state intramolecular cyclization and scission to give a nitrile N-oxide which is trapped by the acrylate. Concurrently, the photoinduced nitro-nitrite inversion also occurs competitively to give the C-nitroso compound which is isolated as the dimer 202. 

The formation of l,2,5-trithiepan-4,6-dicarboxylates was explained by the mechanism depicted in Scheme 85 <20040BC2870>. This reaction presumably involves an initial reduction of 401 to A2-[l,2,3]thiazoline 405, which forms the S,C-biradical 406 by ring opening and release of nitrogen. Dimerization of 406 gives the S,C-biradical 407, which forms a C,C-biradical 409. A tandem intramolecular cyclization-expulsion of acrylic ester from 409 affords the trithiepine- dicarboxylates 402 and 403. An alternative pathway for the reaction would involve the formation of 408 from 406, which would be converted to 409 and then to the products. 

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