Second Generation CaSH (Camphor Sulfonyl Hydrazine) Organocatalysis. Asymmetric Diels-Alder Reactions and Isolation of the Catalytic Intermediate
作者:Qinghua Li、Wai-Yeung Wong、Wing-Hong Chan、Albert W. M. Lee
DOI:10.1002/adsc.201000438
日期:2010.9.10
chiral auxiliary, Oppolzer’s camphor sultam, is turned into the new generation camphor sulfonyl hydrazine (CaSH II) organocatalyst. With the primary hydrazine functionality external to the tricyclic structure, CaSH II is active towards ketone substrates in asymmetric Diels–Alder reactions. The iminium intermediate of the catalytic cycle was isolated. When it was put back into the solution reaction system
Stereoconvergent Direct Ring Expansion of Cyclopropyl Ketones to Cyclopentanones
作者:Jiru Shao、Yue Fu、Sunewang R. Wang
DOI:10.1021/acs.orglett.3c00025
日期:2023.1.27
Recyclization of the ring-opening species of alkyl cyclopropyl ketones to cyclopentanones, which proceeds through an unfavored 5-endo-trig cyclization predicted by Baldwin’s rules, is elusive. Herein, as assisted by a strong aryl donor and the Thorpe–Ingold strain on a quaternary cyclopropyl center, stereoconvergent direct ringexpansion of cyclopropyl ketones to cyclopentanones promoted by TfOH or BF3·Et2O is