AROMATIC RING BROMINATION IN 1,4-BENZOTHIAZINES, 1,4-BENZOXATHIANES AND 1,4-BENZODITHIANES - THE OCCURRENCE OF VICARIOUS NUCLEOPHILIC-SUBSTITUTION OF HYDROGEN AND ELECTROPHILIC AROMATIC-SUBSTITUTION MECHANISMS

Citation
R. Caputo et al., AROMATIC RING BROMINATION IN 1,4-BENZOTHIAZINES, 1,4-BENZOXATHIANES AND 1,4-BENZODITHIANES - THE OCCURRENCE OF VICARIOUS NUCLEOPHILIC-SUBSTITUTION OF HYDROGEN AND ELECTROPHILIC AROMATIC-SUBSTITUTION MECHANISMS, Gazzetta chimica italiana, 126(9), 1996, pp. 595-598
Citations number
14
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry
Journal title
ISSN journal
0016-5603
Volume
126
Issue
9
Year of publication
1996
Pages
595 - 598
Database
ISI
SICI code
0016-5603(1996)126:9<595:ARBI11>2.0.ZU;2-L
Abstract
1,4-benzodithianes, 1,4-benzothiazines and 1,4-benzoxathianes, when tr eated with bromine in anhydrous chloroform, undergo regiospecific mono bromination at the aromatic ring. Based on semiempirical quantum mecha nical calculations, the regiochemistry of the reaction in the case of 1,4-benzothiazines and 1,4-benzoxathianes was shown to be consistent w ith a charge-controlled electrophilic aromatic substitution reaction w here the Br+ species comes from monobromosulfonium ions (as 2). On the contrary, in the case of 1,4-benzodithianes, the bromination is accom plished by Br- via an orbital-controlled vicarious nucleophilic substi tution of hydrogen occurring on dibromodisulfonium ions (as 4).