Rearrangements of 5-Nitronorbornenes. II. 6-Phenyl- and 6-Methyl-5-nitro-2-norbornenes

Rearrangement of the salts of 6-phenyl- (5a) and 6-methyl-5-nitro-2-norbornenes (5b) in aqueous methanolic hydrochloric acid gave isomeric rearrangement products 6a and 6b. Hydrogenation of 6a and 6b over platinum gave dihydro derivatives 9a and 9b and over Raney nickel gave dihydrodeoxo derivatives 12a and 12b, the hydrogenolysis in the latter cases supporting the assignment of hydroxamide structures to 6a and 6b. Ozonolysis of 6a to the known l-phenylpropane-1,2,3-tricarboxylic acid (19), and an independent synthesis of the 3 epimer (17) of the dihydrodeoxo derivative (12a) of 6a, established the structure of 6a as 1,2,3-cis-3a-cis-4,6a-cis-hexa-hydro-1-hydroxy-3-phenylcyclopenta[b]pyrrol-2-one. By analogy the corresponding 3-methyl structure is assigned to 6b. The lactam structure of 12a was extremely resistant to acidic hydrolysis or reduction with LiAlH₄, but epimerized (to 17), particularly under alkaline conditions, whereas 12b did not epimerize, but was readily hydrolyzed (to amino acid hydrochloride 41) and reduced with LiAlH₄ to the amine, 1,2,3-cis-3a-m-4,5,6,6a-cis-octahydro-3-methylcyclopenta [b] pyrrole (42). The mechanism of formation of the rearrangement products is discussed.