139040-85-0Relevant academic research and scientific papers
Isothiourea-Catalyzed Acylative Kinetic Resolution of Tertiary α-Hydroxy Esters
Greenhalgh, Mark D.,Laina-Martín, Víctor,Neyyappadath, Rifahath M.,Qu, Shen,Smith, Andrew D.,Smith, Samuel M.
supporting information, p. 16572 - 16578 (2020/09/09)
A highly enantioselective isothiourea-catalyzed acylative kinetic resolution (KR) of acyclic tertiary alcohols has been developed. Selectivity factors of up to 200 were achieved for the KR of tertiary alcohols bearing an adjacent ester substituent, with both reaction conversion and enantioselectivity found to be sensitive to the steric and electronic environment at the stereogenic tertiary carbinol centre. For more sterically congested alcohols, the use of a recently-developed isoselenourea catalyst was optimal, with equivalent enantioselectivity but higher conversion achieved in comparison to the isothiourea HyperBTM. Diastereomeric acylation transition state models are proposed to rationalize the origins of enantiodiscrimination in this process. This KR procedure was also translated to a continuous-flow process using a polymer-supported variant of the catalyst.
Solvolytic Elimination Reactions of Tertiary α-CSNMe2-Substitutedd Systems
Creary, Xavier,Hatoum, Holia N.,Barton, Angela,Aldridge, Timothy E.
, p. 1887 - 1897 (2007/10/02)
The tertiary benzylic α-CSNMe2-substituted p-nitrobenzoates and trifluoroacetates of general structure Ar(CH3)C(CSNMe2)(OCOR), 7 and 8, solvolyze to give exclusively elimination products H2C=C(CSNMe2)Ar.A Hammett study gave a nonlinear correlation.Variation in rate with solvent ionizing power was small for the unsubstituted trifluoroacetate derivative of 8, and the β-CD3 isotope effect on rate was negligible.There is, however, a large isotope effect (2.5-2.8) in formation of the elimination product when Ph(CH2D)C(CSNMe2)(OCOCF3) solvolyzes.It is concluded that an intermediate must be involved sine the product-determining step and the rate-determining step have differing isotope effects.The likely intermediate is an α-CSNMe2-substituted cation as an ion pair), despite the fact that the reaction has few characteristics of a typical E1 reaction.Tertiary noorbornyl, cyclohexyl, and 2-propyl α-CSNMe2-substituted systems also react to give exclusively elimination products at rates far in excess of α-CONMe2 analogues.It is suggested that α-CSNMe2 cations are also intermediates and that these cations undergo proton loss at an early ion pair stage.These cations are proposed to derive substitantial stabilization by charge delocalization onto sulfur of the thiocarbonyl group. By way of contrast, the secondary system CH3CH(CSNMe2)(OCOCF3), 25, solvolyzes to give mainly a rearranged product CH3CH(CONMe2)(SCOCH3) via a KΔ mechanism involving neighboring thiocarbonyl participation leading to a cyclized ion.
