Nitrobicyclo[2.2.1]heptanes. Part 7. The synthesis of eight isomeric nitrobicyclo[2.2.1]heptan-2-ols and of four isomeric nitrobicyclo[2.2.1 ]heptan-2-ones

Abstract

Diets–Alder reaction of 2-nitropropene and cyclopentadiene yields a separable mixture (85 : 15) of 5-exo-methyl-5-endo-nitrobicyclo[2.2.1 ] heptene (1a) and the endo-methyl-exo-nitro epimer (1b). Hydroboration–oxidation of each in turn gives separable mixtures of 6- and 5-endo-nitrobicyclo[2.2.1 ]heptan-2-exo-ols (2a)/(3a) and the exo-vitro analogues (2b)/(3b) respectively, with the 6-nitro isomers (2) predominating by ca. 3:1 in each case. Oxidation of the four alcohols with ruthenium tetraoxide gives the four ketones (4a), (4b), (5a), and (5b), from which the corresponding endo-alcohols (7) and (8) are prepared by reduction with sodium borohydride or with K-selectride. ¹H and ¹³C N.m.r. data are tabulated for all compounds, and some trends in chemical shifts are described.