1.4- Oxazine, sugar derivatives

The generation of an 1,2-oxazine 4-1 by hetero Diels-Alder reaction is a transformation which opens a versatile array of highly functionalised acyclic and cyclic structures. Thus, pyrrolidine derivatives 4-2, amino alcohols 4-3 and aza sugars 4-4 are easily available from these cycloadducts. Cyclic dienes, e.g. 4-5 are converted into bicyclic adducts 4-6 representing straightforward intermediates for aminocyclitols 4-7 (Fig. 4-1). 

Oxazine ring opening of the sugar spiro derivative 699 with phenylhydra-zine gave the 1,2,4-triazole C-nucleoside 702 through the intermediates shown in Scheme 187 (85CPB102),... 

Cycloadditions of chiral A -acylnitroso compounds have been widely studied. These heterodienophiles are accessible e.g. by oxidation of hydroxamic acid derivatives with periodate. C2-symmetric pyrrolidines lead to high selectivities. 1,2-Oxazines are useful precursors of amino alcohols and aza sugars. 

Reissig and Pfrengle have developed an attractive strategy for the synthesis of 3-amino-2,6-dideoxy sugars. The required starting template 3,6-dihydro-2H-l,2-oxazine was conveniently produced by the addition of lithiated alkoxyallenes (prepared in situ) to o-glyceraldehyde-derived nitrone. ... 

---