Stabilizing N-tosyl-2-lithioindoles with bis(N,N′-dimethylaminoethyl) ether-a non-cryogenic procedure for lithiation of N-tosylindoles and subsequent addition to ketones

A practical procedure suitable for large scale lithiation of N-tosylindoles and subsequent addition to ketones is described. Bis(N,N'-dimethylaminoethyl) ether was found to stabilize 2-lithio-N-tosylindole 1A at -25 degrees C [The temperatures cited are internal temperatures unless otherwise stated]. Addition of this reagent allows the lithiation of N-tosyl indoles and subsequent addition to ketones to operate at -25 degrees C, a temperature suitable for large scale reactions. (C) 2009 Elsevier Ltd. All rights reserved.