Synthesis and reactivity of (1S,4S,5S)-5-bromo-1,3,3-trimethyl-N-nitro-2-oxabicyclo[2.2.2]octan-6-imine. X-Ray molecular structure and absolute configuration of E and Z isomers of (1S,4S)-5,5-dibromo-1,3,3-trimethyl-N-nitro-2-oxabicyclo[2.2.2]octan-6-imine, the first case of separated nitrimine isomers

Abstract

The potassium salt 2 of 1,3,3-trimethyl-N-nitro-2-oxabicyclo[2.2.2]octan-6-imine 1 reacted with bromine in acetic acid solution to give (1S,4S,5S)-5-bromo-1,3,3-trimethyl-N-nitro-2-oxa-bicyclo[2.2.2]octan-6-imine 3. Bromination of the salt 2 in methanolic potassium hydroxide afforded a mixture of (1S,4S)-5,5-dibromo-1,3,3-trimethyl-N-nitro-2-oxabicyclo[2.2.2]octan-6E-and -6Z-imine 4 and 5, whose X-ray crystal-structure determinations allowed their absolute configurations to be established. Bromination of monobromide 3 under different conditions gave the dibromide 4, which was converted into isomer 5 by storage in chloroform solution. Nitrimine 3 reacted with hydroxylamine hydrochloride and sodium hydroxide or piperidine to give (1S,4S,5S)-5-bromo- and -5-hydroxyamino-N-hydroxy-1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-6-imine or (1S,4S,5S)-N-hydroxy-1,3,3-trimethyl-5-(piperidin-1-yl)-2-oxabicyclo[2.2.2]octan-6-imine. Reaction of compound 3 with aliphatic and aromatic primary amines afforded N-substituted (1S,4S,5S)-5-bromo-1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-6-imines. Reduction of compound 3 with sodium cyanoborohydride gave (1S,4S,5S)-5-bromo-1,3,3-trimethyl-N-mtro-2-oxabicyclo[2.2.2]octan-6-amine, whereas consecutive treatment with potassium hydroxide and aq. hydrochloric acid afforded the less stable isomer (1S,4S)-5-bromo-1,3,3-trimethyl-N-nitro-2-oxabicyclo[2.2.2]oct-5-en-6-amine.