Unanticipated Silyl Transfer in Enantioselective α,β-Unsaturated Acyl Ammonium Catalysis Using Silyl Nitronates
作者:Anastassia Matviitsuk、Mark D. Greenhalgh、James E. Taylor、Xuan B. Nguyen、David B. Cordes、Alexandra M. Z. Slawin、David W. Lupton、Andrew D. Smith
DOI:10.1021/acs.orglett.9b04404
日期:2020.1.3
The use of silyl nitronates is reported for the isothiourea-catalyzed synthesis of γ-nitro-substituted silyl esters containing up to two contiguous stereocenters in good yields with excellent enantioselectivities (up to 93% yield and 99:1 er). The serendipitously discovered formation of silyl ester products in this reaction demonstrates a novel platform for catalyst turnover in α,β-unsaturated acyl
作者:Emily R. T. Robinson、Charlene Fallan、Carmen Simal、Alexandra M. Z. Slawin、Andrew D. Smith
DOI:10.1039/c3sc50199j
日期:——
The asymmetric annulation of a range of α,β-unsaturated acyl ammonium intermediates, formed from isothiourea HBTM 2.1 and anhydrides with either 1,3-dicarbonyls, β-ketoesters or azaaryl ketones gives either functionalised esters (upon ring opening), dihydropyranones or dihydropyridones in good yields (up to 93%) and high enantioselectivity (up to 97% ee).
Exploiting the Imidazolium Effect in Base-free Ammonium Enolate Generation: Synthetic and Mechanistic Studies
作者:Claire M. Young、Daniel G. Stark、Thomas H. West、James E. Taylor、Andrew D. Smith
DOI:10.1002/anie.201608046
日期:2016.11.7
function as ammonium enolate precursors in the absence of base. Enantioselective Michael addition–cyclization reactions using different α,β‐unsaturated Michael acceptors have been performed to form dihydropyranones and dihydropyridinones with high stereoselectivity. Detailed mechanistic studies using RPKA have revealed the importance of the “imidazolium” effect in ammonium enolateformation and have highlighted
The Importance of 1,5‐Oxygen⋅⋅⋅Chalcogen Interactions in Enantioselective Isochalcogenourea Catalysis
作者:Claire M. Young、Alex Elmi、Dominic J. Pascoe、Rylie K. Morris、Calum McLaughlin、Andrew M. Woods、Aileen B. Frost、Alix Houpliere、Kenneth B. Ling、Terry K. Smith、Alexandra M. Z. Slawin、Patrick H. Willoughby、Scott L. Cockroft、Andrew D. Smith
DOI:10.1002/anie.201914421
日期:2020.2.24
5-O⋅⋅⋅chalcogen (Ch) interactions in isochalcogenourea catalysis (Ch=O, S, Se) is investigated. Conformational analyses of N-acyl isochalcogenouronium species and comparison with kinetic data demonstrate the significance of 1,5-O⋅⋅⋅Ch interactions in enantioselective catalysis. Importantly, the selenium analogue demonstrates enhanced rate and selectivity profiles across a range of reaction processes including
Isothiourea-mediated asymmetric Michael-lactonisation of trifluoromethylenones: a synthetic and mechanistic study
作者:Louis C. Morrill、James Douglas、Tomas Lebl、Alexandra M. Z. Slawin、David J. Fox、Andrew D. Smith
DOI:10.1039/c3sc51791h
日期:——
HBTM-2.1 promotes the catalytic asymmetric intermolecular Michael-lactonisation of arylacetic acids and trifluoromethylenones in the presence of pivaloyl chloride, giving C(6)-trifluoromethyldihydropyranones with high diastereo- and enantiocontrol (up to 95 : 5 dr and >99% ee) that are readily derivatised to diverse synthetic building blocks containing trifluoromethyl-stereogenicity. Kinetic studies indicate the reaction is first order with respect to both in situ formed mixed anhydride and catalyst concentration, with a primary kinetic isotope effect observed using α,α-di-deuterio 4-fluorophenylacetic acid, consistent with rate determining deprotonation of an intermediate acyl isothiouronium ion.