Trifluoropropenes as Dipolarophiles.
作者:Kiyoshi Tanaka、Takami Mori、Keiryo Mitsuhashi
DOI:10.1246/bcsj.66.263
日期:——
The cycloaddition of C-phenyl-N-methylnitrone with 3,3,3-trifluoropropene and methyl 4,4,4-trifluoro-2-butenoate regio- and stereoselectively gave trans-2-methyl-3-phenyl-5-trifluoromethylisoxazolidine (3a) and methyl 2-methyl-c-3-phenyl-t-5-trifluoromethyl-r-4-isoxazolidinecarboxylate (3b), respectively, as major products. The cycloaddition with 3,3,3-trifluoro-1-nitropropene proceeded regiospecifically to give 2-methyl-c-4-nitro-r-3-phenyl-t-5-trifluoromethylisoxazolidine (3c) and 2-methyl-t-4-nitro-r-3-phenyl-c-5-trifluoromethylisoxazolidine (4c), stereoisomer with 3,4-cis-configuration being predominantly produced. This regioselectivity is explained by both the nitrone-HOMO controlled orbital interaction and the steric hindrance in a transition state. Under more drastic conditions c-3, r-4-isoxazolidine 3b isomerized to the more stable c-3, t-4- and regioisomeric isoxazolidines via 1,3-dipolar cycloreversion. The similar treatment of 3c and 4c resulted in the formation of trans-1-methyl-4-phenyl-3-trifluoromethyl-2-azetidinone.
将 C-苯基-N-甲基硝酮与 3,3,3-三氟丙烯和 4,4,4-三氟-2-丁烯酸甲酯进行环加成,可分别获得反式-2-甲基-3-苯基-5-三氟甲基异恶唑烷(3a)和 2-甲基-c-3-苯基-t-5-三氟甲基-r-4-异恶唑烷羧酸甲酯(3b)作为主要产物。与 3,3,3-三氟-1-硝基丙烯进行环加成反应,可得到 2-甲基-c-4-硝基-r-3-苯基-t-5-三氟甲基异恶唑烷(3c)和 2-甲基-t-4-硝基-r-3-苯基-c-5-三氟甲基异恶唑烷(4c),主要生成 3,4-顺式构型的立体异构体。这种区域选择性可以用硝基-HOMO 受控轨道相互作用和过渡态中的立体阻碍来解释。在更苛刻的条件下,c-3、r-4-异噁唑烷 3b 通过 1,3-二极环转化异构化成更稳定的 c-3、t-4-异噁唑烷和 Regioisisomeric 异噁唑烷。对 3c 和 4c 进行类似处理后,可生成反式-1-甲基-4-苯基-3-三氟甲基-2-氮杂环丁酮。