| Autor: |
Misal Castro LC; Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan., Sultan I; Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan., Nishi K; Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan., Tsurugi H; Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan., Mashima K; Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan. |
| Abstrakt: |
Multifunctionalized indole derivatives were prepared by reducing azoarenes in the presence of ketones and bis(neopentylglycolato)diboron (B 2 nep 2 ) with a catalytic amount of 4,4'-bipyridyl under neutral reaction conditions, where 4,4'-bipyridyl acted as an organocatalyst to activate the B-B bond of B 2 nep 2 and form N , N '-diboryl-1,2-diarylhydrazines as key intermediates. Further reaction of N , N '-diboryl-1,2-diarylhydrazines with ketones afforded N -vinyl-1,2-diarylhydrazines, which rearranged to the corresponding indoles via the Fischer indole mechanism. This organocatalytic system was applied to diverse alkyl cyclic ketones, dialkyl, and alkyl/aryl ketones, including heteroatoms. Methyl alkyl ketones gave the corresponding 2-methyl-3-substituted indoles in a regioselective manner. This protocol allowed us to expand the preparation of indoles having high compatibility with not only electron-donating and electron-withdrawing groups but also N - and O -protecting functional groups. |
