Isoxazolidines sugars

The highly stereoselective 1,3-dipolar cycloaddition of C-phenyl-iV-glycosylnitrones (336) and (679) to dimethyl maleate D14, with the sugar moiety acting as a chiral auxiliary, has been used in enantioselective syntheses of isoxazolidines (678) and (678 ent) (Scheme 2.292) (118). 

Borrachero et al. (180) prepared a number of sugar isoxazolidines by the reaction of carbohydrate-functionalized nitrones with nitroalkenes (Scheme 1.33). They found a matched pair of chiral sugar cycloaddition reaction partners to be... 

A variety of N- and C-nucleoside derivatives in which the sugar unit has been replaced by a functionalised isoxazolidine have been synthesized. The synthetic approaches to different classes of nucleoside analogues such as 115 were all based on 1,3-DC of nitrones <03TA2717, 03TA2419, 03T4733, 03T5231, 03JMC3696>. 

Yokoyama, M, Yamada, N, Togo, H, Synthesis of spiro sugar isoxazolidines via tandem Michael addition-1,3-dipolar cycloaddition, Chem. Lett, 753-756, 1990. 

Isoxazolidines are often used as synthetic precursors of different classes of compounds. Intramolecular cycloaddition of sugar-derived aUcene-nitrones was applied to the synthesis of some chiral cyclopentenone building blocks and natural compounds as exemplified by the synthesis of (-)-neplanocin A 94 starting from D-ribose <05JOC6884>. 

Dipolar cycloadditions between nitrones and alkenes are most useful and convenient for the preparation of isoxazolidine derivatives, which are readily converted to 1,3-amino alcohol equivalents under mild reducing conditions (Tufariello 1984, Torssell 1988). In spite of the importance of chiral amino alcohol units for the synthesis of biologically important alkaloids, amino acids, 3-lactams, and amino sugars, etc. (for a review see Frederickson 1997), catalytic enantioselective 1,3-dipolar cycloadditions remain relatively unexplored (Seerden et al. 1994, 1995, Gothelf and Jorgensen 1994, Gothelf et al. 1996, Hori et al. 1996, Seebach et al. 1996, Jensen et al. 1997). Catalytic enantioselective... 

Abstract This review is devoted to the stereoselectivity of intermolecular (intramolecular cycloadditions are not included) 1,3-dipolar cycloadditions of sugar-derived nitrones. Stereoselective cycloaddition (transformation of isoxazolidine followed by reduction of the N O bond to produce both an amino and a hydroxy function) allows the synthesis of tailor-made products of possible biological interest such as pol>4iydroxylated pyrrolidines, pyrrolizidines, indolizidines, fi-aminocarbonyl compounds, and disaccharides. Attention is focused on the preparation of isoxazolidinyl nucleosides and to the catalysis of the cycloaddition by Lewis acids. This review has concentrated on the new developments achieved from 1999 to February 2007. 

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