OMEGA-ALKENYL ALPHA-NITROALKYL RADICALS .3. RADICAL-CHAIN REACTIONS OF OMEGA-ALKENYL ALPHA-HALOGENONITROALKANES

S(RN)1 reactions between 5-bromo-5-nitrohex-1-ene and the nitronate anions of 2-nitropropane and 5-nitrohex-1-ene failed to give cyclisation of the intermediate alpha-nitroalkyl radical onto the alkene. Reaction between exo-5-bromo-endo-5-nitro-exo-6-phenylbicyclo[2.2.1]hept-2-ene 1 and the anion of 2-nitropropane did not undergo an S(RN)1 reaction and Br+ abstraction gave 2-bromo-2-nitropropane and 5-endo-nitro-exo-6-phenylbicyclo[2.2.1]hept-2-ene. BNAH reduction of exo-5-bromo-endo-5-nitro-exo-6-phenylbicyclo[2.2.1]hept-2-ene 1, 6-bromo-6-nitrohept-1-ene, and 1-bromo-1-nitro-2-(prop-2-enyl)cyclohexane gave the corresponding nitroalkanes without any cyclisation of the intermediate alpha-nitroalkyl radicals. Initial results indicate that an iodine atom transfer methodology provides a possible general method for the cyclisation of omega-alkenyl alpha-nitroalkyl radicals. Cyclisation of intermediate alpha-nitroalkyl radicals, generated by photolysis of 1-(bicyclo[2.2.1]hept-5-en-endo-2-yl)-2-iodo-2-nitropropa 5a, gave a good yield of two diastereoisomeric tricyclic iodonitro compounds 6a and 7a. Photolysis of 1-(bicyclo[2.2.1] hept-5-en-endo-2-yl)-2-iodo-2-nitroethane 5b and 2-(but-3-enyl)-1-iodo-1-nitrocyclohexane 11 also gave the expected products from 5-exo cyclisation of the intermediate alpha-nitroalkyl radicals. The tricyclic iodonitro compound 6a was synthesised from the corresponding endo-methanesulfonate 15, the structure of which was determined by X-ray crystallography.