Gas-phase heteroaromatic substitution. 3. Electrophilic methylation of furan and thiophene by CH<sub>3</sub>XCH<sub>3+</sub> (X = fluoro, chloro) ions
作者:Giancarlo Angelini、Gaetano Lilla、Maurizio Speranza
DOI:10.1021/ja00389a035
日期:1982.12
CH/sub 3/ClCH/sub 3//sup +/ confirms its inherent affinity toward n-type nucleophilic centers by attacking preferentially the heteroatom of 3 and 4. In light of the previous results concerning CH/sub 3/XCH/sub 3//sup +/ methylation of pyrroles, it is concluded that gas-phase attack of CH/sub 3/XCH/sub 3//sup +/ on simple five-membered heteroaromatics is essentially regulated by the electrostatic interaction
先前对 CH/sub 3/XCH/sub 3//sup +/ (X = F 或 Cl) 离子对吡咯和 N-甲基吡咯的气相甲基化进行的辐解研究,来自 CH 的 ..gamma.. 辐解/sub 3/X,扩展为呋喃 (3) 和噻吩 (4)。讨论了通过分子内 1,2 甲基转移发生的取代和随后异构化的机制,并评估了所选亲电子物种的底物和位置选择性。至于吡咯,呋喃和噻吩的气相CH/sub 3/FCH/sub 3//sup +/甲基化的特点是缺乏底物区分(k/sub S//k/sub B/ = 1.2 (3) , 0.8 (4)),伴随着对具有最高负净电荷的底物位置的明显位置选择性(O:..cap alpha..:..beta.. = 36%:35%:29% for 3; S:..cap alpha..:..beta.. = 19%:43%:38% for 4)。相反,CH/sub 3/ClCH/sub