The Nucleophilic 5<i>-endo-trig</i> Cyclization of 1,1<i>-</i>Difluoro-1-alkenes: Ring-Fluorinated
Hetero- and Carbocycle Synthesis and Remarkable Effect of
the Vinylic Fluorines on the Disfavored Process
作者:Junji Ichikawa、Yukinori Wada、Masaki Fujiwara、Kotaro Sakoda
DOI:10.1055/s-2002-33912
日期:——
The disfavored 5-endo-trig cyclizations have been accomplished for 1,1-difluoro-1-alkenes with nitrogen, oxygen, sulfur, and carbon nucleophiles by taking advantage of the properties of fluorine. β,β-Difluorostyrenes bearing tosylamido, hydroxy, or methylsulfinyl group at the o-position undergo intramolecular nucleophilic substitution with a loss of the vinylic fluorine, leading to 2-fluorinated indole, benzo[b]furan, and benzo[b]thiophene in high yields. 1,1-Difluoro-1-butenes bearing homoallylic tosylamido, hydroxy, mercapto, or iodomethyl group also successfully cyclize via a 5-endo-trig process with the in situ generated intramolecular nucleophiles to afford 2-fluoro-2-pyrroline, 5-fluoro-2,3-dihydrofuran, 5-fluoro-2,3-dihydrothiophene, and 1-fluorocyclo-pentene. The two vinylic fluorines proved to be essential and play a critical role in these ‘anti-Baldwin’ cyclizations.
利用氟的特性,1,1-二氟-1-烯与氮、氧、硫和碳等亲核物进行了不受欢迎的 5-endo-trig 环化反应。o-位上带有对甲苯磺酰胺基、羟基或甲基亚磺酰基的δ²,δ²-二氟苯乙烯在失去乙烯基氟的情况下发生分子内亲核取代反应,从而高产出 2-氟化吲哚、苯并[b]呋喃和苯并[b]噻吩。含有同源烯丙基甲苯胺基、羟基、巯基或碘甲基的 1,1-二氟-1-丁烯也成功地与原位生成的分子内亲核物通过 5-endo-trig 过程发生环化反应,生成 2-氟-2-吡咯啉、5-氟-2,3-二氢呋喃、5-氟-2,3-二氢噻吩和 1-氟环戊烯。事实证明,在这些 "反鲍德温 "环化反应中,两个乙烯基氟是必不可少的,并发挥着关键作用。