Hexopyranos-3 -ulose 1,6-anhydro

Ci.,H2 O10 l,6-Anhydro-2,3-0-isopropylidene-/ -D-arafeino-hexopyranos-3-ulose dimer APARHD 43 238... 

Formation of l,2 5,6-di-0-isopropylidene-a-D-n7i( -hexo-furanos-3-ulose (Fig. 2.13, 2.4.2.1 Table 2.3) was one of the first carbohydrate oxidations effected by stoich. RuOyCCl [310, 311]. The reagent was also used for oxidation of 1,6-anhydro-3,4-0-isopropylidene-P-D-galactopyranose to the -P-D-/yxo-hexopyranos-2--ulose, part of a route leading to 1,6-anhydro-P-D-talopyranose (Fig. 2.15) [321]. 

D. Horton and E. K. Just, Stereospecific chain-branching by C-alkylation at the ketonic and enolic positions of l,6-anhydro-2,3-0-isopropylidene-beta-D-lyxo-hexopyranos-4-ulose, Carbohydr. Res. IS 81 (1971). D. C. Baker, D. K. Brown, D. Horton, and R. G. Nickol, Synthesis of branched-chain sugar derivatives related to algarose, Carbohydr. Res. 32 299 (1974). 

Anhydro-4-O-benzyl-2-deoxy-2-fluoro-/J-D-n 60-hexopyranos-3-ulose (13) Typical Procedure 199... 

M. Cerny, L. Kalvoda, and J. Pacak, Syntheses with anhydro sugars 5. Preparation of 2,4-di-O-substituted l,6-anhydro-/i-D-hexopyranos-3-uloses and their isomerization and reduction, Collect. Czech. Chem. Commun., 33 (1968) 1143-1156. 

S. Caron, A. I. McDonald, and C. H. Heathcock, An improved synthesis of 1,6-anhydro-2,3-di-0-benzyl-/ -D-xylo-hexopyranos-4-ulose, Carbohydr. Res., 281 (1996) 179-182. 

K. Heyns, J. Weyer, and H. Paulsen, Katalysche oxidation von 1.6-Anhydro-/ -D-xylo-hexopyranos-3-ulose, Ber., 98 (1965) 327-333. 

The Baeyer-Villiger transformation of several protected derivatives having a free ketone group has been effected by m-chloroperoxybenzoic acid. Thus, 1,6-anhydro-3,4-0-isopropylidene-/f-D-/yxn-hexopyranos-2-ulose (28) was converted into the cyclic, orthoacid anhydride 29.67 As an additional example, the Baeyer-Villiger oxidation of Ferrier carbocyclization products derived from D-glucose afforded 5-deoxyhexofuranosiduronic acids, via the ring-expanded lactonic intermediates68 (Scheme 12). 

When the carbonyl group enolized is at a secondary position, the hydrogen can be introduced into four possible adjacent positions, potentially leading to a mixture of four isomers. These possibilities can be decreased if the sugar is held in a rigid conformation so that enolization can take place in one direction only. For example, 1,6-anhydro-2,3-0-isopropylidene-/3-D-lyxo-hexopyranos-4-ulose (10) can-... 

The acetonation of dimers having cis, vicinal hydroxyl groups under the catalysis of perchloric acid yields the corresponding isopropylidene acetals417,460 in addition, the dimers of 1,6-anhydro-R-D-xyfo-hexopyranos-3-ulose and l,6-anhydro-/3-i>arabino-hexopyranos-3-ulose yield very interesting, acid-stable spiro-acetals417 (76 and 77),... 

The unexpected formation of dimeric forms, as well as of hydrates (especially of glycos-2-uloses) somehow complicates the interpretation of the n.m.r. and c.d. (see Sect. IV,17,c) spectra of the unsubstituted glycosuloses in aqueous solution, all of these compounds exist in chair conformations5,417,419,455 (l,6-anhydro-j8-D-rifeo-hexopyranos-3-ulose contains a considerable proportion of dimers417,419). The boat conformation of certain glycos-4-uloses419 seems not to have been unambiguously proved. 

The aldolization mentioned was subsequently used461 for an interesting synthesis of branched-chain sugars. Thus, on reaction with formaldehyde, 78 gives, stereospecifically, 1,6-anhydro-3-C-(hydro xy-methyl)-2,3-0-isopropylidene-/3-D-(yxo-hexopyranos-4-ulose, which subsequently undergoes reduction at C-4 by a crossed Cannizzaro reaction leading to l,6-anhydro-3-C-(hydroxymethyl)-2,3-0-isopropyl-idene-/3-D-talopyranose. On the other hand, an attempt to condense 78 with ethyl formate did not result in the expected 3-C-formyl derivative only the dimer 88 was obtained.461... 

The n.m.r. spectrum of l,6-anhydro-2,3-0-isopropylidene-)S-D-/y3CO-hexopyranos-4-ulose (27) in deuterochloroform provides a good example of virtual long-range coupling. Since H-2 and H-3 have identical chemical shifts at 5-52 x the signal for H-1 at 4 37 x appears... 

A further example of the complexity of the structures of derivatives of hydroxy-carbonyl carbohydrates is provided by l,6-anhydro-j3-D-crabmo-hexopyranos-3-ulose (8) which exists as the dimer (9) (see Vol. 5, p. 107), but gives the iso-propylidene compounds (10) (with a rearranged structure) as well as the diacetal... 

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