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Monomeric cinchona alkaloid-based catalysts for highly enantioselective bromolactonisation of alkynes.

Research paper by Michael M Wilking, Constantin G CG Daniliuc, Ulrich U Hennecke

Indexed on: 12 Oct '16Published on: 12 Oct '16Published in: Chemistry - A European Journal



Abstract

The cinchona alkaloid dimer (DHQD)2PHAL has been shown to be a broadly applicable catalyst for asymmetric halogenations. However, this catalyst does not have to be dimeric and a class of monomeric quinidine and quinine-derived catalysts was prepared which shows often superior selectivities in bromolactonisations of terminal alkynoic acids. Mechanistic investigations show that these organocatalysts act as host molecules that can bind carboxylic acid-based substrates as guests with substantial binding constants. Based on these findings it is proposed that this class of catalysts is bifunctional in nature activating the halogenating agent as well as the nucleophile in electrophilic halogenation reactions.