Ozonolyses of Enantiopure 4‐Alkoxy‐3,6‐dihydro‐2H‐1,2‐oxazines:An Expedient Route to Functionalized α‐Amino‐β‐hydroxy Esters

Ozonolysis and subsequent in situ acylation/base treatment converted the enantiopure carbohydrate‐derived 1,2‐oxaz‐ines 1 , 5 , 8 (either syn ‐ or anti ‐configured) and anti ‐ 11 into the highly functionalized α‐amino‐β‐hydroxy esters 2 , 6 , 9 and 12 in moderate to good yields. Ketals of 5‐hydroxylated 1,2‐oxazines (e.g., syn ‐ 3 ) were formed as side products in most cases; the reactions of precursors syn ‐ and anti ‐ 8 even provided the ketals syn ‐ or anti ‐ 10 as major components. The synthesized functionalized amino esters are valuable intermediates, as demonstrated by the subsequent transformation of anti ‐ 2 into the enantiopure building blocks 13 – 15 . Since precursor 1,2‐oxazines were prepared via lithiated alkoxyallenes, the latter species were serving as formyl ester anion equivalents. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)