In the presence of magnesium perchlorate, 1,3-dipolar cycloaddition reactions of nitrile oxides to crotonamide bearing 4-benzyl-5,5-dimethyl-1,3-oxazolidin-2-one as the chiral auxiliary proceeded with a regio- and diastereo-selective manner to afford the corresponding chiral 2-isoxazoline. The mechanisms underlying the diastereoface selection in the cycloaddition reaction were investigated using the B3LYP/6-31G* level of theory.
For reviews, see: (a) CurranD.P. (ed.), Advances in Cycloaddition, JAI Press Inc., Greenwich, 1988, Vol 1; 1990, Vol 2; 1993, Vol.3; (b) A. Padwa (Ed.), 1,3-Dipolar Cycloaddition Chemistry, John Wiley & Sons, Inc.: Toronto, 1984; Vols 1 and 2; See also: (c) J.-H. Chu, W.-S. Li, I. Chao, G.-H. Lee and W.-S. Chung, Tetrahedron, 2006, 62, 7380; (d) S. Gao, Z. Tu, C.-W. Kuo, J.-T. Liu, C.-M. Chu and C.-F. Yao, Org. Biomol. Chem., 2006, 4, 2851; (e) J.B.F.N. Engberts, E. Fernandez, L. Garcia-Rio and J.R. Leis, J. Org. Chem., 2006, 71, 6118; (f) K. Bala and H.C. Hailes, Synthesis, 2005, 3423.
2.
(a) JiangH., ZhaoJ., HanX., and ZhuS., Tetrahedron, 2006, 62, 11008; (b) U. Groselj, D. Bevk, R. Jakse, A. Meden, B. Stanovnik and J. Svete, Tetrahedron: Asymmetry, 2006, 17, 1217; (c) M. Benltifa, S. Vidal, D. Gueyrard, P.G. Goekjian, M. Msaddek and J.-P. Praly, Tetrahedron Lett., 2006, 47, 6143; (d) S.P. Waters, M.W. Fennie and M.C. Kozlowski, Org. Lett., 2006, 8, 3243.
3.
YamamotoH., WatanabeS., HasegawaM., NoguchiM., and KanemasaS., J. Chem. Res., (S), 2003, 284.
Some of these results have been reported in Jpn. Kokai Tokkyo Koho, JP 2003-321470 (Application No. JP 2002-122134 (24th Apr. 2002).
6.
In recent years, Lewis acid supported stereocontrol in nitrile oxide cycloaddition reactions has been developed independently, but efficiency of the stereoselection was less satisfactory with the Lewis acid: (a) FaitaG., PaioA., QuadrelliP., RancatiF., and SeneciP., Tetrahedron, 2001, 57, 8313; (b) G. Faita, A. Paio, P. Quadrelli, F. Rancati and P. Seneci, Tetrahedron Lett., 2000, 41, 1265; (c) P. Micúch, L. Fisera, M.K. Cyranski, T.M. Krygowski and J. Krajcik, Tetrahedron, 2000, 56, 5465; (d) P. Micúch, L. Fisera, M.K. Cyranski and T.M. Krygowski, Tetrahedron Lett., 1999, 40, 167.
7.
While we were carrying out this work (see ref.5), Sibi et al. also reported a enantioselective nitrile oxide cycloaddition reaction: SibiM.P., ItohK., and JasperseC.P., J. Am. Chem. Soc., 2004, 126, 5366.
8.
The absolute configuration of the isoxazoline l-3a was identified by reductive removal9 of the chiral auxiliary with L-Selectride® followed by comparison of the optical rotation of the obtained isoxazolin-5-ylmethanol with that of the authentic one.10
9.
OppolzerW., KingmaA.J., and PillaiS.K., Tetrahedron Lett., 1991, 32, 4893.
10.
KanemasaS., and OnimuraK., Tetrahedron, 1992, 48, 8645.
