The chiral optically pure five-membered 3-tert-butoxy-1-pyrroline N-oxide (1) was synthesized by a convenient five-step procedure from diethyl L-malate. The key step is the regioselective HgO dehydrogenation of the N-hydroxypyrrolidine 6 obtained by double-nucleophilic displacement of a (bis)mesylate with hydroxylamine. A rationalization of the observed regioselectivity of the oxidation by studying the oxidation of a deuterated N-hydroxypyrrolidine 20 is reported. Nitrone 1 has been applied to the synthesis of a new (lS,7S,8aR)-1,7-dihydroxyindolizidin(e2 8) via 1,3-dipolar cycloaddition strategies.
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Cicchi et al. (1995) studied this question.