John O. Hoberg

SYNTHESIS AND REACTIONS OF UNSATURATED SUGARS

Publisher Summary This chapter discusses the synthesis and reactions of unsaturated sugars. Sugar derivatives that contain double bonds have been developed and used so extensively that they almost certainly constitute the most versatile category of carbohydrate compounds available for use in synthesis of unsaturated sugars. They may be applied both in the synthesis of complex members of the family and of a myriad enantiomerically pure noncarbohydrate compounds—notably, many of interest in medicinal chemistry. In addition, some unsaturated sugar derivatives have themselves been found to possess important therapeutic properties. The unnatural L-nucleoside inhibits reverse transcriptase and shows potent and selective anti-AIDS activity. This chapter surveys the chemistry of most of the important types of monosaccharide derivatives that contain single alkene groups—notably, the glycols that are extremely valuable starting materials for a vast range of synthetic transformations. It also discusses the preparation of the reactions of glycols, elaborates the synthesis of pyranoid and furanoid 2- and 3-Enes, and explains the chemistry of endo-Enes and exo-Enes.

Synthesis and chemistry of cyclopropanated carbohydrates

This review provides a synopsis of the formation and chemistry of cyclopropanated carbohydrates. The organization begins with methods for the formation of the cyclopropanated carbohydrate followed by the chemistry of the bicyclic system. Examples of new reactions and rearrangements leading to new products and the synthesis of natural products are presented.

Cyclopropanation and ring-expansion of unsaturated sugars

Abstract The cyclopropanation of unsaturated sugars provides 1,2 C -methylene carbohydrates in good to excellent yields. Treatment of the cyclopropanes with a Lewis acid furnishes seven-membered oxacycles.

Cyclopropanation of unsaturated sugars with ethyl Diazoacetate

The cyclopropanation of unsaturated sugars with ethyl diazoacetate and a metal catalyst provides ester-substituted 1,2-C-methylene carbohydrates in good to excellent yields. Ring opening of the cyclopropane has also been achieved providing C-2 branched glycosyl bromides.

Catalytic oxidation of para-substituted phenols with nitrogen dioxide and oxygen

Abstract A series of para-substituted phenols was oxidized to the corresponding benzoquinones in moderate to high yield with catalytic amounts of NO2 under O2 in MeOH. Little or no oxidation is observed under argon. Substrates of lower reactivity gave quinones when treated with stoichiometric amounts of NO2 in CCl4, but nitration of the aromatic ring became a significant side product.

Heptanosides from galactose-derived oxepenes via stereoselective addition reactions.

Addition reactions to a 3,4-anhydroheptanose gave heptanoside analogues of carbohydrate derivatives in good to excellent stereochemical purity. Characterization of the products by (1)H and (13)C NMR, COSY, HSQC-DEPT, HMBC, 1D TOCSY, and NOE experiments were performed to obtain the stereochemistry of addition. The 3,4-anhydroheptanose used in this study is obtained from the ring-expansion of a cyclopropanated galactal and thus demonstrates the synthetic utility of heptanose synthesis via cyclopropanated carbohydrates.

Potassium Channel Activators Based on the Benzopyran Substructure: Synthesis and Activity of the C-8 Substituent

The synthesis of a series of methoxy bearing 2,2-dimethyl-2H-1-benzopyrans have been achieved for testing as potassium channel activators. The synthesis involves formation of 6-cyano-8-methoxy-2,2-dimethyl-2H-1-benzopyran from vanillin, epoxidation, then ring opening of the epoxide with nitrogen nucleophiles to produce the new benzopyrans. Biological testing showed a dramatic decrease in activity thus revealing an important site of activity in this class of compounds.

Monoesterification of di-O-isopropylidene and di-O-cyclohexylidene chiro-inositols

Monoesterification of D- or L-chiro-inositols protected as diacetals proceeds in excellent selectivity and yields. The metal-catalyzed, one-step reaction proceeds at room temperature under an air atmosphere and has been developed using a range of examples.

Heteropolyacid Catalyzed Oxidation of Lignin and Lignin Models to Benzoquinones

Abstract Several metal catalysts were examined for their effectiveness in activating hydrogen peroxide and oxygen as oxidants for conversion of lignin models to benzoquinones. Good yields of quinones were observed when certain heteropolymetallates were used as catalysts in the presence of hydrogen peroxide. Oxygen was generally less effective. Oxidation of lignin samples gave 2-3 wt% yields of 2,6-dimethoxybenzoquinone.

Inositols as chiral templates: 1,4-conjugate addition to tethered cinnamic estersElectronic supplementary information (ESI) available: experimental details for the preparation and analysis of compounds 3, 4, 6, 7, 8a?e, 10a, 10b, 10e, 11a?11d, 13a, 13b and 13d. See http://www.rsc.org/suppdata/ob/b4/b408467e/

The 1,4-addition of thio nucleophiles to chiro-inositols containing a cinnamyl Michael acceptor proceeded with excellent diastereochemical induction and good yields. Cleavage of the inositol auxiliary provides beta-thio hydrocinnamic acids in >99% ees.