Asymmetric 1,3-dipolar cycloaddition of optically active trifluoromethylated α,β-unsaturated aryl sulfones with nitrones: the use of o-dialkylaminoethyl chiral auxiliaries
作者:Hiroyasu Tsuge、Takashi Okano、Shoji Eguchi、Hiroshi Kimoto
DOI:10.1039/a606890a
日期:——
Optically active trifluoromethylated α,β-unsaturated
aryl sulfones 8aâc, which have a chiral
N,N-dialkylaminoethyl group on the
ortho position, were synthesized from
(S)-1-phenylethylamine 2 and ethyl trifluoroacetate.
Asymmetric 1,3-dipolar cycloaddition of sulfones 8aâc with some
selected nitrones 9aâc gave the corresponding isoxazolidines
10aâc, 11aâc and 12â15 regio- (> 98%) and
diastereo-selectively (36â56% de) in 58â80% yields. The
absolute configurations of the cycloadducts were assigned on the basis
of X-ray crystallographic analysis of the adduct 10a and by the
1H NMR spectra. The obtained facial selectivity was
rationalized by comparison of four possible stable conformers of
compound 8a based on AM1 calculations.
具有手性N,N-二烷基氨基乙基的邻位光学活性三氟甲基化α,β-不饱和芳基砜8a~c,由(S)-1-苯乙胺2和乙基三氟乙酸酯合成。硫酮8a~c与一些选定的硝酮9a~c进行不对称1,3-偶极环加成反应,得到相应的异噁唑啉10a~c、11a~c和12~15,其区域选择性(>98%)和非对映选择性(36~56% de)在58~80%的产率。环加合物的绝对构型是通过对加合物10a的X射线晶体结构分析和1H NMR谱分配的。通过基于AM1计算的化合物8a的四种可能的稳定构象的比较,解释了所获得的表面选择性。