Cyclic nitronates asymmetric diastereoselectivity, nitrone

Py used a nitrone-alkene coupling in a short, asymmetric synthesis of (+ )-hyacinthacine A2 (Scheme 5.43).74 The key carbon-carbon bond-forming step in their approach involved the highly diastereoselective reductive coupling of the L-xylose-derived cyclic nitrone 66 to ethyl acrylate.74... 

Carbamoyl nitroso dienophiles, derived from chiral pyrrolidines, have been generated and their reactivity with cyclohexa-diene investigated. Using (—)-fra/w-2,5-dimethylpyirolidine as the auxiliary, the [4 + 2] cycloadduct is isolated in 82% yield and with 98% diastereomeric excess (eq 10). Similarly, chiral ynamine dienophiles have been utilized in asymmetric [4 + 2] cycloadditions with a,p-unsaturated nitroalkenes to afford cyclic nitronic esters. The resulting esters subsequently undergo a rapid [1,31-rearrangement to afford chiral cyclic nitrones in moderate yield and high diastereoselectivity (eq 11)-... 

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