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Synthesis and isolation of iodocarbazoles. Direct iodination of carbazoles by N ‐iodosuccinimide and N ‐iodosuccinimide‐silica gel system
Author(s) -
Bonesi Sergio M.,
ErraBalsells Rosa
Publication year - 2001
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570380111
Subject(s) - chemistry , halogenation , carbazole , reagent , dichloromethane , chloroform , electrophilic substitution , acetic acid , silica gel , electrophilic aromatic substitution , sulfuric acid , reactivity (psychology) , electrophile , proton nmr , medicinal chemistry , organic chemistry , solvent , catalysis , medicine , alternative medicine , pathology
Carbazole ( 1 ) undergoes electrophilic aromatic substitution with various iodinating reagents. Although, 3‐iodocarbazole ( 1b ) and 3,6‐diiodocarbazole ( 1d ) obtained by iodination of carbazole were isolated and characterized sometime ago, 1‐iodocarbazole ( 1a ), 1,6‐diiodocarbazole ( 1c ) and 1,3,6‐triiodocarbazole ( 1e ) had never been isolated from the reaction mixture. The preparation and subsequent isolation and characterization of 1a, 1b, 1c, 1d and 1e are reported (mp, t r , R f , 1 H‐nmr, 13 C‐nmr and ms). As iodinating reagents, NaIO 4 /I 2 and NaIO 4 /KI mixtures in (i) ethanol doped with catalytical amount of sulfuric acid and in (ii) acetic acid, and N ‐odosuccinimide and N ‐iodosuccinimide‐silica gel in dichloromethane and in chloroform have been used and their uses have been compared. The iodination reaction of different carbazole derivatives such as 2‐acetoxycarbazole ( 2 ), 3‐bromocarbazole (3) and 3‐nitrocarbazole ( 4 ) was also studied and the corresponding iododerivatives, 2a, 2b, 2c, 3a, 3b, 4a and 4b , are described for the first time. Semiempirical PM3 calculations have been performed in order to predict reactivity of carbazole ( 1 ), substituted carbazoles (2‐4) and iodocarbazoles ( 1a‐1e, 2a‐2c, 3a‐3b, 4a and 4b ) (Scheme 1). Theoretical and experimental results are discussed briefly.