The Nucleophilic 5-endo-trig Cyclization of 1,1-Difluoro-1-alkenes: Ring-Fluorinated Hetero- and Carbocycle Synthesis and Remarkable Effect of the Vinylic Fluorines on the Disfavored Process

Junji  Ichikawa; Yukinori  Wada; Masaki  Fujiwara; Kotaro  Sakoda

doi:10.1055/s-2002-33912

FEATUREARTICLE

The Nucleophilic 5-endo-trig Cyclization of 1,1-Difluoro-1-alkenes: Ring-Fluorinated Hetero- and Carbocycle Synthesis and Remarkable Effect of the Vinylic Fluorines on the Disfavored Process

Junji Ichikawa*, Yukinori Wada, Masaki Fujiwara, Kotaro Sakoda
Department of Chemistry, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Fax: +81(3)58414345; e-Mail: junji@chem.s.u-tokyo.ac.jp;

Abstract

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Abstract

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.

Key words

cyclizations - fluorine - alkenes - heterocycles - carbocycles

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