Department of Chemistry and Biochemistry, Texas Tech University , Lubbock, Texas 79409-1061, United States.
School of Chemistry and Materials Science, Jiangsu Normal University , Xuzhou 221116, P. R. China.
J Org Chem. 2017 Mar 17;82(6):2992-2999. doi: 10.1021/acs.joc.6b03068. Epub 2017 Mar 8.
Asymmetric [3 + 2] cycloaddition of chiral N-phosphonyl imines with methyl isocyanoacetate has been established, enabling controllable/switchable stereoselectivity access to 21 examples of cycloadducts with good to excellent chemical yields (up to 92%) and high diastereoselectivities (up to 99:1 dr). The cycloaddition reaction promoted by CsCO resulted in diastereoenriched (4R,5S)-products with >99:1 dr. However, it showed the reverse stereoselectivity as diastereoenriched (4S,5R) products when AgF was employed as the catalyst. The synthesis followed the group-assisted purification (GAP) chemistry/technology in which the pure 2-imidazoline products were readily provided by washing the crude products with cosolvents of hexane and ethyl acetate.
手性 N-磷酰亚胺与甲基异氰酸酯的不对称 [3 + 2]环加成已经建立，可控制/切换立体选择性地得到 21 个环加成产物，具有良好到优异的化学收率（高达 92%）和高的非对映选择性（高达 99:1 dr）。CsCO 促进的环加成反应得到了非对映体过量的（4R,5S）-产物，具有>99:1 dr。然而，当 AgF 作为催化剂时，它表现出相反的立体选择性，得到非对映体过量的（4S,5R）产物。该合成遵循基团辅助纯化（GAP）化学/技术，其中通过用己烷和乙酸乙酯的共溶剂洗涤粗产物，可轻易地得到纯的 2-咪唑啉产物。
