On the nature of the chain-extending species in organolithium initiated stereospecific reagent-controlled homologation reactions using α-chloroalkyl aryl sulfoxides
摘要:
The reaction of an organolithium with an alpha-chloroalkyl aryl sulfoxide ostensibly generates an alpha-chloroalkyllithium by sulfoxide lithium exchange, but the actual identity of the chain-extending species in chlorosulfoxide-based StReCH reactions is not certain. To explore this issue, racemic 2-cyclohexyl (4R*, 5R*)-4,5-diphenyl-1,3,2-dioxaborolane was homologated by treatment with scalemic (S)-chloromethyl phenyl sulfoxide and n-BuLi (THF, -78 degrees C). The reaction proceeded without a detectable level of kinetic resolution, a finding consistent with chloromethyllithium being the active chain-extending species rather than a chiral sulfurane intermediate. (C) 2014 Elsevier Ltd. All rights reserved.
Mechanism and optimisation of the homoboroproline bifunctional catalytic asymmetric aldol reaction: Lewis acid tuning through in situ esterification
作者:Irene Georgiou、Andrew Whiting
DOI:10.1039/c2ob06872a
日期:——
homoboroproline as a bifunctionalcatalyst in the asymmetricaldolreaction has been investigated mechanistically, particularly with respect to tuning the Lewis acidity of boron by in situ esterification with mildly sigma-electron withdrawing diols such as hydrobenzoin and tartrate esters. The stability of simple cyclohexyl and cyclopentyl boronate diol esters shows that the 5-ring boronate esters are more stable