O-isopropylidene derivatives

In principle, a number of different types of acetal or ketal might be produced. In this section, we want to exemplify a small number of useful reactions in which two of the hydroxyl groups on the sugar are bound up by forming a cyclic acetal or ketal with a snitable aldehyde or ketone reagent. Aldehydes or ketones react with 1,2- or 1,3-diols under acidic conditions to form cyclic acetals or ketals. If the diol is itself cyclic, then the two hydroxyl groups need to be cA-oriented to allow the thermodynamically favourable fused-ring system to form (see Section 3.5.2). Thus, dx-cyclohexan-1,2-diol reacts with acetone to form a cyclic ketal, a 1,2-O-isopropylidene derivative usually termed, for convenience, an acetonide. 

The reaction involving 2,3-O-benzylidene sugars was then extended to a study of the behavior of 1,2-O-isopropylidene derivatives.272 Furanoid derivatives 262 and 263 gave, respectively, (+)-(S)-(E)-5-butyl-l-methoxy-3-nonen-2,5-diol (264) (yield 23%) and ( + )-2(R),3(S)-(E)-6-butyl-l,2-dimethoxy-4-decen-3,6-diol (265) (yield 21%). On the other hand, acetal derivatives of the D-arabino (266) and... 

Other procedures frequently adopted involve periodate oxidation of a suitable acetal derivative,63 and borohydride reduction of acetals of lactones.64 It has also proved feasible to interchange acetals by means of acid catalysis55,56 thus, reaction of a 1,2-O-isopropylidene derivative of D-glucose with benzaldehyde and sulfuric acid afforded the corresponding 1,2-O-benzylidene derivative. 

Antibiotics and Components Thereof.—Pillaromycin [the component sugar was shown to be 2,3,6-trideoxy-4-C-(hydroxymethylcarbonyl)-L-t/rr ( -hexose] (246), 5-deoxy-3-C-formyl-jS-L-lyxofuranose trimethylene dithioacetal, and the corresponding 1,2-O-isopropylidene derivative. ... 

In contrast to the oxidation of acyclic polyhydric alcohols in benzene,508 treatment of 1,2-O-isopropylidene-a-D-glucofuranose with silver carbonate-on-Celite in boiling methanol led to selective oxidation of the primary hydroxyl group, with the formation of the al-duronic acid derivative in 68% yield.517... 

For the synthesis of D-glucuronic acid, methods of oxidation of suitable D-glucose derivatives have been devised during the past two decades these procedures have been comprehensively reviewed by Marsh,6 Mehltretter,7 and Heyns and Paulsen.8 For special purposes, for example, for the preparation of 6-I4C-labelled D-glucuronic acid, chain-extension reactions of 1,2-O-isopropylidene-a-D-xy/o-pen-todialdo-I,4-fiiranose by the cyanohydrin synthesis9 or by ethynyla-tion10 are used, but these frequently yield mixtures of D-glucuronic acid and L-iduronic acid. 

In ortho-annelated, bicyclic, furanoid sugar derivatives, because of lessened conformational flexibility, only a limited number of conformations is thermodynamically favored. The preponderance of the 3T2 conformation found for (furanoid) 1,2-O-isopropylidene-a-D-gluco-and -/8-L-ido-furanoses,76,80 1,2-O-benzyIidene-a-D-glucofura-nose,81 and l,2-0-isopropyIidene-5-0-p-tolylsuIfonyl-a-n-glucofura-nurono-6,3-lactone76 (52) confirms this. 

The simplified preparations128 of 5-O-sulfonylated derivatives of 1,2-O-isopropylidene-a-D-gIucofuranose (77 and 78) (see Section VI,4) was the key to substantial improvements in the synthesis of L-idose. 

Using the C-5 epimeriztion strategy used to convert D-glucose into L-idose, but starting with a D-galactoseptanose derivative (such as 47) delivered the L-altrose isomer 50 (Scheme 10). Treatment of 5-O-benzyl-1,2-O-isopropylidene-a-D-galactoseptanose... 

Deamination performed in hydrochloric acid solution may result in the formation of chlorine-containing products, as illustrated by the deamination of 5-amino-5-deoxy-l,2-0-isopropylidene-a-D-xylo-furanose, which gave the 5-chloro-5-deoxy derivative (isolated in 6% yield).49 1,2-O-Isopropylidene-a-D-xylofuranose, the major prod-... 

Application of this method to 1,2-O-isopropylidene-a-D-pentodialdo-1,4-furanoses [144a,b (Ref. 272) and 144c (Ref. 273)] gave the corresponding 4-C-(hydroxymethyl) derivatives (145a-c), and various nucleosides of them were also synthesized. 

O-isopropylidene-jS-D-fructopyranose via the 1-O-tosyl- or 1-deoxy-l-iodo derivatives.265 Related 1,2-anhydro-a- and /J-D-fructofuranose and... 

A similar rearrangement has been performed on furanosic derivatives, by a Sn2 displacement of a triflate protecting group at C-5, using sodium trifluoroacetate.173 Thus, 1,2-0-isopropylidene-/l-L-idofuranurono-6,3-lactone (59) has been prepared from 1,2-O-isopropylidene-a-D-glucofuranu-rono-6,3-lactone (40). 

D. Horton and J.-H. Tsai, Preparation of derivatives of L-idose and L-iduronic acid from 1,2-O-isopropylidene-a-D-glucofuranose by way of acetylenic intermediates, Carbohydr. Res., 58 (1977) 89-108. 

---