α-chloronitroso compounds derived from carbohydrate ketones:: cycloadditions with cyclic dienes, a synthesis of (-)-physoperuvine and a formal synthesis of (+)-epibatidine

1,2-O-Isopropylidene-alpha-D-xylofuranose 9 was converted into 5-O-(tert-butyldiphenylsilyl)-3-chloro-3-deoxy-1,2-O-isopropylidene-3-C-nitroso-alpha-D-xylofuranose 17 in four steps, and a similar alpha-chloronitroso compound 8 was synthesised from 1,2:5,6-di-O-isopropylidene-alpha-D-glucofuranose 6, the structures of 8 and 17 being confirmed by X-ray crystallography. Reaction of 8 or 17 with cyclohexa-1,3-diene in the presence of small amounts of water gave the cycloadduct (1S,4R)-3-aza-2-oxabicyclo[2.2.2]oct-5-ene, as its hydrochloride (-)-2, in greater than or equal to 96% ee. Reactions of either 8 or 17 with cyclohepta-1,3-diene similarly gave (1R,5S)-7-aza-6-oxabicyclo[3.2.2]non-8-ene hydrochloride (-)-25 with greater than or equal to 96% ee, but reactions with cyclopentadiene proceeded differently, with 17 giving the nitrone (E)-(3R,5R)-3-[5'-O-(tert-butyldiphenylsilyl)-3'-deoxy-1',2'-O-isopropylidene-alpha-D-erythro-pentofuranos-3'-ylideneamino]-5-chlorocyclopentene N-oxide 19, the structure of which was determined by X-ray crystallography. The dihydrooxazines (-)-25 and (-)-2 were used in syntheses of (-)-physoperuvine (-)-34 and (+)-epibatidine (+)-40, respectively. A pseudoenantiomeric alpha-chloronitroso compound 51 was also prepared from 2,3-O-isopropylidene-alpha-L-sorbofuranose 44, and reaction of 51 with cyclohexa-1,3-diene gave (+)-2 with 97% ee.