Glycals furanose

Synthesis from exo-glycals. Several routes to C-l glycals from 1-exo-methylene pyranoses and furanoses have been described recently. 

Scheme 41 Synthesis a furanose-fused butyrolactone from a glycal-derived cyclopropane...

Other avenues of research were not ignored, however, as is indicated by the preparation of the first furanose-related glycal and the study of inversions in the cyclitol series by treatment of their esters with liquid hydrogen fluoride. Then, in the mid-sixties, Dr. Fletcher began to turn to the chemistry of acylamidodeoxyhexoses. Together with Drs. Nevenka Pravdic and T. D- Inch, he prepared 1,2-ox-azoline derivatives of such carbohydrates. This led to a method for... 

McDonald, F. E. Gleason, M. M. Asymmetric synthesis of nucleosides via molybdenum-catalyzed alkynol cycloisomerization coupled with stereoselective glycosylations of deoxy-furanose glycals and 3-amidofuranose glycals. J. Am. Chem. Soc. 1996, 118, 6648-6659. 

Aryltin reagents have been used similarly to arylaluminum compounds for the preparation of C-glycosides. Particularly applied to reactions with furanose glycals, Daves, etal.,77>78 carried our the reactions shown in Schemes 2.4.2 and 2.4.3. Utilizing palladium acetate to mediate the couplings between glycals and aryltributyltin compounds, p anomeric selectivity was observed in poor to good yields. 

As illustrated in Schemes 4.1.4 through 4.1.9, the use of pyrimidinyl mercuric acetates have been instrumental in the development of C-nucleosides. Although the comparison in Scheme 4.1.9 illustrates the utility of aryl iodides in addition to aryl mercury compounds, the nature of the specific reagents were quite different. As shown in Scheme 4.1.11, Zhang, etal.,10 utilized pyrimidinyl iodides in the preparation of C-nucleosides from furanose glycals. As illustrated, the product mixture composition was highly susceptible to the specific reaction conditions used. Thus, of the two products shown, either is available in comparable yields. 

Ness, R. K., and H. G. Fletcher, Jr. 2-Deoxy-D-er> f/iro-pentose. X. Synthesis of l,4-Anhydro-3,5-di-0-benzoyl-2-deoxy-D-er> //iro-pentose-l-enol. Derivatives of a Furanose-related Glycal. J. Organ. Chem. (U.S.A.) 28, 435 (1963) Haga, M., and R. K. Ness Preparation and Properties of 3,5-Di-0-p-anisoyl-l,2-dideoxy-D-er> t/iro-pentofuranose-l-ene. Various p-Anisoylated Derivatives of D-Ribofuranose. J. Organ. Chem. (U. S. A.) 30, 158 (1965). 

A detailed study on the conventional benzoylation and pivaloylation of d-fructose has been undertaken following consideration of factors such as equilibration rates and the distribution of tautomeric forms at given temperatures, practical procedures for the selective preparation of either pyranose, furanose, or acyclic peresters have been worked out. The selectivities in electrochemically induced esterifications of D-glycals have been investigated and compared with selectivities in chemically induced ester formations. ... 

Reaction of otherwise protected furanose and pyranose 1,2-diols with methanesulphonyl chloride and triethylamine, followed by treatment of the resulting 2-0-mesylaldosyl chlorides with excess of active zinc dust and iodide ion,gave the corresponding substituted glycals in high yields. ... 

The glycosidic bonds present in KS-502 and rebeccamycin provided especially attractive contexts for evaluation of the glycal epoxide method (Scheme 13). Treatment of the furanose glycal with DMDO gave the furanose epoxide 69 ster-eoselectively [38]. Reaction of this epoxide with the phenol 70 afforded an 81% yield of the desired aryl-glycoside 71. Subsequent steps completed the synthesis of KS-501 (42) and KS-502 (43). These furanoid epoxides were also used in the synthesis of nucleosides [39]. 

---