Abstract
Treatment of 1-chloromethylbenzotriazole (4) with salicylonitrile (5a), thiosalicylonitrile (5b), ethyl N-(2-cyanophenyl)carbamate (5c), and N-(2-cyanophenyl)methane-sulfonamide (5d) provided the corresponding intermediates 3. Cyclization of compounds 3a-3c with LDA gave 2- (1H-benzo(d)(1,2,3)triazol-1-yl)benzofuran-3-amine (2a), 2-(1H-benzo(d)(1,2,3)triazol-1- yl)benzo(b)thiophen-3-amine (2b), and ethyl 3-amino-2-(1H-benzo(d)(1,2,3)triazol-1-yl)-1H- indole-1-carboxylate (2c), respectively. Attempts to accomplish elimination of the benzotriazole nitrogen under both thermal and photolytic conditions failed.
Highlights
The Gewald reaction is a well known method of preparation of 2-aminothiophene derivatives.1Its modifications have been used for the synthesis of 3-amino-2-EWG substituted benzofurans,2a,2b,3a,3b benzothiophenes,3a,3b,4 and 1H-indoles.3a The EWG groups includes esters,2a,2b,4a,4b,4c,4d nitriles,2a,4a,4c nitro,4a, and acyl groups2a,2b,3a,3b,4a,4c,5 (Scheme 1)
We have utilized this methodology as a key step of the synthesis of tetracyclic benzofuro[3,2-b]quinolines, benzothieno[3,2-b]quinolines and indolo[3,2-b]quinolines6
1H NMR spectrum (CDCl3; 30 °C) : δ 2.45 s, 6H (COCH3); 7.40-7.54 m, 4H
Summary
The Gewald reaction is a well known method of preparation of 2-aminothiophene derivatives.1Its modifications have been used for the synthesis of 3-amino-2-EWG substituted benzofurans,2a,2b,3a,3b benzothiophenes,3a,3b,4 and 1H-indoles.3a The EWG groups includes esters,2a,2b,4a,4b,4c,4d nitriles,2a,4a,4c nitro,4a, and acyl groups2a,2b,3a,3b,4a,4c,5 (Scheme 1). Available 1-chloromethyl-1H-benzotriazole 4 treated with the corresponding 2-substituted benzonitriles 5 provided good yields of compounds 3a-d (Scheme 4). The following starting compounds were prepared by the previously published methods: thiosalicylonitrile (5b),3a ethyl N-(2-cyanophenyl)carbamate (5c),11 and N-(2cyanophenyl)methanesulfonamide (5d).
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