Nitrobicyclo[2.2.1]heptanes. Part 8. Neighbouring-group participation by nitro groups during the reaction of endo-nitrobicyclo[2.2.1 ]heptenes with electrophiles

Abstract

Cyclic dienes 1 undergo Diels–Alder reactions with several nitroalkenes 2 to give adducts in which the endo-nitro isomers 3 are the major constituents. These isomers react with N-bromosuccinimide in methanol to produce regio- and stereo-selectively functionalised nitrotrinorbornanols 5, which result from neighbouring-group participation by the nitro group during electrophilic bromination. A mechanistic proposal is presented together with evidence for the intermediacy of nitronate esters 10, and the scope of the reaction is briefly explored. Reactions of endo-nitrotrinorbornenes 3 with mercury(II) trifluoroacetate in methanol give more cis,exo-methoxymercuriation product 14 than nitrogroup-participation product 13. An apparently unprecedented ⁴J¹⁹⁹Hg–¹H coupling in the former is described.