N–H Insertion reactions of rhodium carbenoids. Part 3.1 The development of a modified Bischler indole synthesis and a new protecting-group strategy for indoles
N–H Insertion reactions of rhodium carbenoids. Part 3.1 The development of a modified Bischler indole synthesis and a new protecting-group strategy for indoles
N–H Insertion reactions of rhodium carbenoids. Part 3.1 The development of a modified Bischler indole synthesis and a new protecting-group strategy for indoles
作者:Katherine E. Bashford、Anthony L. Cooper、Peter D. Kane、Christopher J. Moody、Sendogagounder Muthusamy、Elizabeth Swann
DOI:10.1039/b202666j
日期:2002.7.11
A modified version of the Bischler indole synthesis has been developed in which the key step is the NâH insertion reaction of rhodium carbene intermediates derived from α-diazo-β-ketoesters with anilines. Thus N-methylanilines 1 react with diazoketoesters 2 in the presence of dirhodium(II) acetate to give (N-arylamino)ketones 3, cyclisation of which using boron trifluorideâethyl acetate or acidic ion exchange resin gives the indoles 4. In order to extend this method to the synthesis of N-unsubstituted indoles, a new protecting group strategy for indoles was developed. In this, anilines are reacted with α,β-unsaturated-esters or -sulfones to give the conjugate addition products 6 and 9,
cyclisation of which gives indoles 8 and 11. The N-(2-ethoxycarbonylethyl)- and -(2-sulfonylethyl)- protecting groups are readily removed from indoles 8 and 11 by treatment with base.
作者:Katherine E Bashford、Anthony L Cooper、Peter D Kane、Christopher J Moody
DOI:10.1016/s0040-4039(01)02047-0
日期:2002.1
The 2-phenylsulfonylethyl group is a useful alkyl protecting group for nitrogen during indole synthesis; it is readily removed from the indole nitrogen under basic conditions. (C) 2001 Elsevier Science Ltd. All rights reserved.