Department of Chemistry, Loughborough University, Loughborough, Leics, UK LE11 3TU.
Org Biomol Chem. 2011 Jan 7;9(1):297-306. doi: 10.1039/c0ob00529k. Epub 2010 Nov 29.
N-Alkylation of optically active 1-benzyl-4-phenyl-4,5-dihydroimidazole with active alkyl halides and treatment of the so-formed 4,5-dihydroimidazolium ions with DBU in the presence of a range of electron-deficient alkene dipolarophiles, constitutes a 'one-pot' cascade terminating in a 1,3-dipolar cycloaddition reaction that affords optically active pyrrolo[1,2-a]imidazoles. Three bonds of the so-formed pyrrolidine moiety are constructed in this cascade. The cycloaddition follows an endo approach of dipole and dipolarophile with anti geometry of the dipole and facial selectivity derived from the phenyl substituent. Inter- and intramolecular cycloaddition modes are observed.
用活泼的卤代烷对光学活性的 1-苄基-4-苯基-4,5-二氢咪唑进行 N-烷基化，然后在一系列缺电子烯烃偶极子存在下，用 DBU 处理所形成的 4,5-二氢咪唑鎓离子，构成“一锅煮”级联反应，最终发生 1,3-偶极环加成反应，得到光学活性的吡咯并[1,2-a]咪唑。在这个级联反应中构建了形成的吡咯烷部分的三个键。环加成遵循内型方式，偶极子和偶极子的反式几何形状来自于苯基取代基的面选择性。观察到了分子间和分子内的环加成模式。
