Additions of lithiated alkoxyallenes to D-glyceraldehydebased nitrones 1 and 2 did not provide the expected hydroxylamine derivatives. Instead, a novel [3+3] cyclization process furnished 4-alkoxy-3,6-dihydro-2H-1,2-oxazines 9-14 with excellent syn selectivities and in moderate to good yields. Through precomplexation of the nitrones the corresponding anti-configured 1,2-oxazines 9, 10 and 13 could be obtained with high stereoselectivity. The reactions of nitrones 3-6, derived from D-erythrose or D-threose, generally proceeded less diastereoselectively, but reasonable yields of anti-configured 1,2-oxazines such as anti-17 and anti-19 could be obtained under Lewis acid promotion conditions. This was also the case for reactions of the D-arabinose-derived nitrone 7, which provided the anti-1,2-oxazines 23 and
Crystallographic Data and X-ray Structure Analysis of 13a. Crystals of 13a are triclinic, space group PI: a -10.91 (1) b = 9.570 (3), c = 8.758 (8) A; a = 65.15 (1), ß = 66.94 (3), y = 71.24 (1)°; Z = 2; dc = 1.21 g cm"3. Intensities were measured by using Mo Ka radiation [Philips PW1100 diffractometer, graphite monochromator, 6-29 scan mode, 3 < 6 < 25°, scan speed 0.025°s "1, scan width deg 1.7 + 0.6 tan 9], The total number of independent reflexions measured was 2384. The structure was solved by direct methods31 and refined by full-matrix least-squares32 to a final R-factor of 4.8%. In the refinements 1934 reflections with intensities greater than the standard deviation from counting statistics were used. Hydrogen atoms were found from difference Fourier syntheses. In the last cycles 263 parameters were refined (scale factor, extinction parameter, positional
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