Nitrones, addition carbohydrate-derived

Nitrones also works as precursors of amines via nucleophilic addition of organoaluminum species. Desvergnes and Py et al. described the effective addition of dimethylalkynylaluminum reagents to carbohydrate-derived chiral nitrones 32 (Scheme 29) [51]. This strategy enables diastereoselective access to optically active N-hydroxy pyridine derivatives 33 having four stereogenic centers. 

Pillard C, Desvergnes V, Py S (2007) Diastereoselective addition of alkynylalanes to carbohydrate-derived nitrones. Tetrahedron Lett 48 6209-6213... 

Influenced by the ZnMe2-assisted addition of terminal aJkynes to nitrones developed by Chavant et al. [119,120], Micouin et al. performed the same type of reaction using AlMes and obtained several propargylic hydroxylamines [121], For a stereoselective variant, Desvergnes, Py, et al. prepared the carbohydrate-derived nitrone 74, but only achieved high diastereoselectivities in the additirm of phenylacetylene (Scheme 14b) [122]. Moreover, the preformed alkynyl alane had to be used because in situ formation from AlMes and the aUcyne predominantly led to methyl addition. From the reaction of stereoisomeric nitrones of the type 74, it was concluded that the diastereoselectivity solely depended on the configuration at C-3. 

A wide array of compounds undergo the Nef reaction. These include simple nitro compounds, as well as complex multifunctional species. For example, the carbohydrate in equation (2) was isolated as its hy-drazone derivative in 72% yield. Nitronate anions generated in situ can be acidified to give good yields of aldehydes and ketones. As an illustration, Michael addition of the dianion of hexanoic acid to 2-nitro-propene gives the expected keto acid after acidification (equation 3). ... 

Cyclization by Addition of Amines to Multiple Bonds of Carbohydrate Substrates. A versatile unsaturated aldehydic intermediate derived from D-ribose has been used to synthesize a number of potential glycosidase inhibitors (Scheme 13). Addition of hydroxylamine and then bromine to the enal resulted in the formation of nitrone 57 with 66% diastereoselectivity, and this in turn was readily transformed into various imino-alditols (e.g. 5R-60) by nucleophilic attack followed by reduction. A number of these compounds proved to be good inhibitors of a-L-fucosidases. ... 

The nitrone 266 bearing a D-gulono-y-lactone auxiliary directs addition of methylmagnesium bromide as a key step in synthesis of (/7)-zilegton (Scheme 54). The gulonic-acid derived auxiliary 267 has been described as an improvement on a previously reported carbohydrate oxazolidinone auxilary (see Chapter 10)... 

When phenylglyoxylate esters derived from various carbohydrate alcohols Eire employed in the Patemo-Buchi reaction with furan, the products (107) can show up to 80% diastereomeric excess.The nitrone (108) underwent facially-selective addition to the appropriate alkene to give adduct (109) ... 

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