17682-71-2

Mono- and di-O-isopropylidene-l-sorbofuranose derivatives are important starting materials for the synthesis of modified sugars and useful chiral compounds. However, several inconsistencies in the spectral data of these compounds and erroneous structural assignments have been noted in the literature. The unambiguous synthesis of 1,2:4,6-di-O-isopropylidene-α-l- sorbofuranose and derivatives of 1,2- and 2,3-O-isopropylidene-α-l- sorbofuranoses has been achieved and definitive spectral data on these compounds are provided.

In the title compounds, C12H20O6, (I), and C9H16O6, (II), the five-membered furan-ose ring adopts a 4 T 3 conformation and the five-membered 1,3-dioxolane ring adopts an E 3 conformation. The six-membered 1,3-dioxane ring in (I) adopts an almost ideal O C 3 conformation. The hydrogen-bonding patterns for these compounds differ substanti-ally: (I) features just one intra-molecular O - H...O hydrogen bond [O...O = 2.933 (3) A], whereas (II) exhibits, apart from the corresponding intra-molecular O - H...O hydrogen bond [O...O = 2.7638 (13) A], two inter-molecular bonds of this type [O...O = 2.7708 (13) and 2.7730 (12) A]. This study illustrates both the similarity between the con-formations of furan-ose, 1,3-dioxolane and 1,3-di-oxane rings in analogous isopropyl-idene-substituted carbohydrate structures and the only negligible influence of the presence of a 1,3-dioxane ring on the conformations of furan-ose and 1,3-dioxolane rings. In addition, in comparison with reported analogs, replacement of the -CH2OH group at the C1-furan-ose position by another group can considerably affect the conformation of the 1,3-dioxolane ring.

1,2-O-Isopropylidene-α-D-xylofuranose 9 was converted into 5-O-(tert-butyldiphenylsilyl)-3-chloro-3-deoxy-1,2-O-isopropylidene-3-C-nitroso- α-o-xylofuranose 17 in four steps, and a similar α-chloronitroso compound 8 was synthesised from 1,2:5,6-di-O-isopropylidene-α-o-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 ≥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 ≥96% ee, but reactions with cyclopentadiene proceeded differently, with 17 giving the nitrone (E)-(3 R,5 R)-3-[5′-O-(tert-butyldiphenylsilyl)-3′-deoxy-1′,2′-O-is opropylidene-α-D-erythro-pentofuranos-3′-ylidene-amino]-5-chlorocycl opentene 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 α-chloronitroso compound 51 was also prepared from 2,3-O-isopropylidene-α-L-sorbofuranose 44, and reaction of 51 with cyclohexa-1,3-diene gave (+)-2 with 97% ee.

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