Enantioselective, Desymmetrizing Bromolactonization of Alkynes
摘要:
Asymmetric bromolactonizations of alkynes are possible using a desymmetrization approach. The commercially available catalyst (DHQD)(2)PHAL promotes these cyclizations in combination with cheap NBS as a bromine source to give bromoenol lactones in high yield and with high enantioselectivity. The bromoenol lactone products, containing a tetrasubstituted alkene and a quaternary stereocenter are valuable building blocks for synthetic chemistry.
Monomeric Cinchona Alkaloid-Based Catalysts for Highly Enantioselective Bromolactonisation of Alkynes
作者:Michael Wilking、Constantin G. Daniliuc、Ulrich Hennecke
DOI:10.1002/chem.201604003
日期:2016.12.19
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, often showing superior selectivity in bromolactonisations of terminal alkynoic acids. Mechanistic investigations show that these organocatalysts act as