ω-Alkenyl α-nitroalkyl radicals. Part 3. Radical chain reactions of ω-alkenyl α-halogenonitroalkanes

Abstract

S_RN1 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 α-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_RN1 reaction and Br⁺ abstraction gave 2-bromo-2-nitropropane and 5-endo-vitro-exo-6-phenylbicyclo[2.2.1]hept-2-eve. BNAH reduction of exo-5-bromo-endo-5-nitro-exo-6-phenylbicyclo[2.2.1]hept-2-eve 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 α-nitroalkyl radicals. Initial results indicate that an iodine atom transfer methodology provides a possible general method for the cyclisation of w-alkenyl α-nitroalkyl radicals. Cyclisation of intermediate α-nitroalkyl radicals, generated by photolysis of 1 -(bicyclo[2.2.1 ]hept-5-en-endo-2-yl)-2-iodo-2-nitropropane 5a, gave a good yield of two diastereoisomeric tricyclic iodonitro compounds 6a and 7a. Photolysis of 1 -(bicyclo[2.2.1]hept5-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 α-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.