Thomas C. Crawford

The synthetic utility of amine borane reagents in the reduction of aldehydes and ketones

Abstract Primary and secondary amine boranes have been shown to be mild, efficient, and stereoselective reducing agents for aldehydes and ketones in protic or non-protic solvents with reactivity patterns different than diborane or sodium borohydride.

Synthesis of L-Ascorbic Acid

Publisher Summary This chapter provides a summary of the methods developed for the synthesis of L-ascorbic acid. L -Ascorbic acid is a white, crystalline solid melting at 192°C and having, in water, a specific rotation at the sodium D line of +24°. In solution, L -ascorbic acid has a pK 1 of 4.17 and a pK 2 of 11.79. The more-acidic proton has been shown by both chemical and physical methods to be that of the 3-hydroxyl group. The structure of L-ascorbic acid in solution has been studied by C-NMR spectroscopy, suggesting that a variety of tautomeric structures is possible. L-Ascorbic acid has also been synthesized from D-galacturonic acid —a hexose derivative not as readily available as D-glucose. In the chapter, the methods of preparation of precursors in the various syntheses are discussed. Many of the methods used for the preparation of analogs are based on the procedures used for the synthesis of L -ascorbic acid. The synthesis and biological activity of a number of these analogs are reviewed in the chapter.

Nucleophilic catalysis in the insertion of silicon halides into oxiranes: A synthesis of o-protected vicinal halohydrins

Abstract Silicon halides in the presence of nucleophilic catalysts react with epoxides to form O-protected vicinal halohydrins with enhanced regioselectivity.

The Gulono-1,4-Lactones A Review of Their Synthesis, Reactions, and Related Derivatives

Publisher Summary This chapter presents a review of the synthesis, reactions, and related derivative of the gulono-1,4-lactones. The most efficient synthesis of L -gulono-1,4-lactone entails the reduction of D -glucofuranurono-6,3-lactone, which can be obtained from D -glucose. D -Gulose has also been prepared by the oxidation of 4,6- O -ethylidene-l, 2- O -isopropylidene-α- D -galactopyranose, followed by reduction and hydrolysis. The addition of hydrogen cyanide to D -xylose resulted in the formation of cyanohydrins which on hydrolysis, afforded a mixture of D -gulonic acid and D -idonic acid. It has also been reported that D -galactose can be isomerized with molybdic acid to a mixture containing D -talose and D -gulose, but the yields are low. A number of derivatives of gulono-1,4-lactone have been prepared that, by reduction, would provide selectively protected derivatives of gulose. It is found that when L -gulono-1,4-lactone was treated with benzaldehyde and concentrated sulfuric acid, 2, 6:3, 5-di-O-benzylidene- L -gulono-1,4-lactone is formed. A variety of amino derivatives of L -gulonic acid has also been reported. The miscellaneous derivatives of the gulono-1,4-lactones are also elaborated.

An efficient synthesis of L-ascorbic acid and [5-2H1]-L-ascorbic acid

L-Ascorbic acid has been synthesized via the regio- and stereo-selective reduction of D-threo-2,5-hexodiulosonic acid; this procedure also can be used for preparation of the 5-deuterio-compound.