Auxiliary accelerated reactions: Towards the use of catalytic chiral auxiliaries
摘要:
In competition experiments, the acceleration of reactivity of alkenes tethered to pyridyl groups compared with the corresponding alkenes tethered to phenyl groups in the presence of transition metals was demonstrated for two reaction types: Diels-Alder cycloaddition of enoate esters and catalytic hydrogenation of allylic and homoallylic ethers. The rate accelerations observed are of crucial importance in the development of a new concept for asymmetric catalysis: chiral auxiliaries which can function in a catalytic manner. (C) 1997 Elsevier Science Ltd.
Diastereoselective conversion of sulfides into sulfoxides. 1,5- and 1,6-asymmetric induction
作者:Justin F. Bower、Christopher J. Martin、David J. Rawson、Alexandra M. Z. Slawin、Jonathan M. J. Williams
DOI:10.1039/p19960000333
日期:——
The diastereoselective oxidation of sulfides into sulfoxides has been achieved with enantiomerically pure dihydrooxazole auxiliaries. When an additional hydroxymethyl substituent is present, diastereocontrol is very high and 1,5-asymmetric induction has been achieved with up to 96 : 4 selectivity, and 1,6-asymmetric induction has been achieved with up to 97 : 3 selectivity in the absence of any additional chiral agents.
Arylsulfides containing an enantiomerically pure oxazoline in the ortho-position have been oxidised to the corresponding sulfoxides with a variety of reagents. When the oxazoline unit contains a 4-hydroxymethyl group, good levels of diastereocontrol have been obtained using mCPBA (96:4) or t-butylhydroperoxide and titanium tetraisopropoxide (97:3) as the oxidant. This diastereocontrol provides an effective
Auxiliary accelerated reactions: Towards the use of catalytic chiral auxiliaries
作者:Andrew D. Westwell、Jonathan M.J. Williams
DOI:10.1016/s0040-4020(97)00829-6
日期:1997.9
In competition experiments, the acceleration of reactivity of alkenes tethered to pyridyl groups compared with the corresponding alkenes tethered to phenyl groups in the presence of transition metals was demonstrated for two reaction types: Diels-Alder cycloaddition of enoate esters and catalytic hydrogenation of allylic and homoallylic ethers. The rate accelerations observed are of crucial importance in the development of a new concept for asymmetric catalysis: chiral auxiliaries which can function in a catalytic manner. (C) 1997 Elsevier Science Ltd.