Phosphine-Catalyzed Formal Oxa-[4 + 2] Annulation Employing Nitroethylene and Enones: Enantioselective Synthesis of Dihydropyrans
作者:Zhichao Jin、Huanzhen Ni、Bo Zhou、Wenrui Zheng、Yixin Lu
DOI:10.1021/acs.orglett.8b02519
日期:2018.9.7
The first phosphine-catalyzed enantioselective formal oxa-[4 + 2] reaction between nitroethylene and α-cyano-α,β-unsaturated ketones has been developed. In the presence of a dipeptide-based phosphine catalyst and achiral Brønsted acid additives, highly functionalized 3,4-dihydro-2H-pyrans were obtained with excellent enantio- and diastereoselectivities.
Enantioselective Amine-Catalyzed [4+2] Annulations of Allenoates and Oxo-dienes: An Asymmetric Synthesis of Dihydropyrans
作者:Xiaojun Wang、Tong Fang、Xiaofeng Tong
DOI:10.1002/anie.201100945
日期:2011.5.27
dihydropyrans have been prepared in high to excellent yields and enantioselectivities (see scheme). The interaction between functional groups in the zwitterionic intermediate, which is generated by addition of the amine catalyst to the allenoate substrate, is thought to play a crucial role in the stereochemical outcome. Bn=benzyl, DMAP=4‐dimethylaminopyridine.