Ribose 4,5-0-isopropylidene acetal

Thio-D-ribose (20) was first reported by Clayton and Hughes [44,45], an improved s)mthesis from D-ribono-1,4-lactone was published in 2002 [46]. Isopropylidene acetals [47] as well as 1,4-anhydro derivatives thereof [48] have also been made available. 

Using acetone-copper(II) sulfate only, Morgenlie24 found that D-ribose affords 20% each of the 2,3- (furanose) and 3,4- (pyranose) isopropylidene acetals. With acid-catalyzed reactions, only the former is generally obtained. Thermodynamic stability is a feature of two cis-fused, five-membered rings. Likewise, good yields of the 3,4-0-... 

Using the n.m.r. method described above,the isopropylidenations of D-ribose diethyldithioacetal and of D-erythritol have been re-examined. The former with acetone-sulphuric acid was shown to give the 2,5 3,4- and the 2,3 4,5-diacetals each in 40% yield and not the 2,4 3,5-diacetal as previously claimed. D-Erythritol gave mainly the 1,2,3,4-di-O-isopropylidene acetal with either acetone or 2,2-dimethoxypropane-toluene-p-sulphonic acid. ... 

The known adduct (385) of furan and vinylene carbonate, previously used for the synthesis of some cyclitols,256,257 has been transformed into DL-ribose derivatives. After hydroxylation of 385 and subsequent formation of the isopropylidene derivative, the carbonate group was removed by treatment with barium hydroxide, and the resulting diol was cleaved by oxidation with permanganate. Dicarboxyl-ic acid 386 gave, upon treatment with acetic anhydride, cyclic anhydride 387. The reaction of 387 with azidotrimethylsilane produced... 

The condensation of acetone with D-ribose, with sulfuric acid as the catalyst, has also been examined in detail.17 The major component is 2,3-O-isopropylidene-D-ribofuranose (59%), together with three minor components l,5-anhydro-2,3-0-isopropylidene-D-ribofuranose (9%), 1,2 3,4-di-O-isopropylidene-a-D-ribopyranose (3%), and 1,2-0-isopropylidene-a-D-ribofuranose (6%). The authors observed that the only marked difference when other catalysts (such as copper sulfate or zinc chloride) were used was the absence of the anhydro compounds. Assuming that the 1-hydroxyl group is equatorial, the preponderance of the 2,3-acetal is consistent with the thermodynamic stability of the isomer having the least number of endo substituents and with the unfavorable interactions between the acetal rings in the 1,2 3,4-diacetal, which possesses a cis-syn-cis arrangement of rings.10... 

When D-ribose was exposed to acetone and sulphuric acid in the presence of formaldehyde the unusual derivative (5) was formed in >80% yield. Mild acid hydrolysis removed the isopropylidene group preferentially. 1-Carboxyethylidene derivatives (pyruvate acetals) have been synthesized from vicinal bis-silyl ethers of hexopyranosides by reaction with methyl or ethyl pyruvate in the presence of trimethylsilyl triflate. An example is given in Scheme 1. By use of methyl pyruvate diphenyldithioacetal and... 

The (Z)-isomer (245) of l-0-acetyl-2,3 4,5-di-0-isopropylidene-D-cr> //iru-pent-l-enitol was obtained on heating 2,3 4,5-di-0-isopropylidene- W /fyi u-D-arabinose or the o-ribose analogue with an excess of acetic anhydride containing sodium acetate. Acetic anhydride and sodium acetate also converted 2,3 4,5-di-<9-isopropylidene- W Ayf/o-D-xylose into the (Z)-D-//zA-eo-pent-1-enitol (246), which, like (245), could be photoisomerized to the ( )-isomer. 

---