Nitrones sugar-derived

Fisera L (2007) 1,3-Dipolar Cycloadditions of Sugar-Derived Nitrones and their Utilization in Synthesis. 7 287-323... 

Sugar-derived nitrones were used to synthesize derivatives unsubstituted at the nitrogen atom such as 588 and 590 (Schemes 144 and 145 (method A)). Similarly, homo-N,0-nucleosides were prepared using allyl nucleobases as dipolarophiles <2006T1171>. 

SCHEME 10.21 Generation of chiral spiro isoxazohdines from sugar-derived nitrones. 

Dipolar Cycloadditions of Sugar-Derived Nitrones and their Utilization in Synthesis... 

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. 

It should be mentioned that the stereoselectivity of cycloaddition of chiral sugar-derived nitrone to an alkene is difficult to predict, and would appear to be dependent on minor structural changes in either component. Three structural features can influence the stereochemical outcome of nitrone/alkene cycloadditions /Z nitrone isomerization about the C = Nbond, alkene or/and nitrone facial selectivity, and endolexo preferences [6j. 

Intramolecular 1,3-DC of sugar-derived nitrones followed by reductive cleavage of the isoxazolidine N-0 bond have been used in the synthesis of aminocyclopentitols and anellated carbasugar derivatives <01TL4925, 0ITL5769, 01EJO759>. In all the reported examples the polycyclic isoxazolidines were obtained with high or complete diasteroselectivity. 

A few years later, the same authors reported a second synthesis of hyacinthacine A2 starting from the same sugar-derived nitrone 31 [14]. This approach was very close to the one previously described by Martin et al. [12], the key step being based on the RCM of the same diolefin intermediate 29 (Scheme 5). The nucleophilic addition of vinylmagnesium bromide onto 31 led diastereoselectively to hydroxylamine 36, proceeding by the less... 

Strategy relies on the reductive coupling between a sugar-derived nitrone 31 and a simple acrylate bearing the three carbon centers required to achieve the B-ring formation, after reduction of the N—O bond and ring-closure from VIII (Scheme 10). 

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