Expeditious synthesis of multisubstituted indoles via multiple hydrogen transfers
1Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan. k_mori@cc.tuat.ac.jp.
Abstract:
Described herein is the expeditious construction of multi-substituted indole skeletons via multiple hydrogen transfers. When ortho-amino ketoesters were treated with a catalytic amount of TiCl4 in the presence of 1.0 equivalent of dehydrating reagent, three types of hydrogen transfer processes ([1,5]-hydride shift, proton transfer, and [1,2]-hydride shift) occurred to give various 3-alkoxycarbonylindoles. Further study revealed that a [1,2]-alkyl shift instead of a [1,2]-hydride shift proceeded to afford 3-alkylindoles from the substrates with an amino group having tertiary carbons adjacent to a nitrogen atom.
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