Regioselectivity associated with the 1,3-dipolar cycloaddition of nitrones with electron-deficient dipolarophiles

Abstract

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

The Effects of Lewis Acid on the 1,3-Dipolar Cycloaddition Reaction of C-Arylaldonitrones with Alkenes.

“…Major product from the reaction of Nmethylnitrone (1b) with ethyl acrylate (2A) has been reported to be not 3A but 3A. 49) The result differs from our one. Therefore, a reduction was carried out to the major product with a view to obtaining definite information on the structure.…”

“…These results are consistent with previous studies on 1,3-dipolar cycloaddition reaction of nitrone. [1][2][3][42][43][44][45][46][47][48][49][50] The formation and the ratio of two stereoisomers can be explained on the basis of both electronic and steric factors as follows. Aldonitrones such as 1a have been known to be stable in Z-configuration.…”

“…Aldonitrones such as 1a have been known to be stable in Z-configuration. [1][2][3][42][43][44][45][46][47][48][49][50]52) Monosubstituted alkenes such as 2C-M have been known to have relatively high HOMO and to undergo exclusively a dipole-LUMO/dipolarophile-HOMO controlled reaction with the Z-aldonitrone (1a) (see Chart 7). [1][2][3] Though the reaction proceeds with high regioselectivity, the stereoselectivity of the reaction was poor one.…”

Diastereoselectivity in the Reaction of N‐Glycosyl‐nitrones: 1,3‐Dipolar Cycloaddition and Addition of Phosphite Anion

“…'syn' attack in the addition to methyl methacrylate is 85:15 and for the addition of methyl acrylate 59 :41, in favour of the 'syn' attack. This may be due to a stronger interaction of the nitrone HOMO with the LUMO of the acrylate than with the LUMO of the methacrylate [4] [5]. The lower regioselectivity found in the cycloaddition of acrylate (see also [6] [7]) corresponds well with this explanation, which implies that HOMO-controlled cycloadditions would favour a 'syn' attack.…”

Asymmetric 1,3-dipolar cycloadditions of acrylamides

“…For example, the cycloaddition of N-methyl-C-phenylnitrone with acrylonitrile gives the trans 5-substituted isomer as the major product, whereas in the reaction with nitroethene the cis 4-substituted isomer predominates (Scheme 37). 121 …”