Bifunctional phosphonium/thioureas derived from tert-leucine behaved as highly selective catalysts for enantioselective protonation of enol esters, providing α-chiral ketones in yields of up to 99% with high enantioselectivities (up to 98.5:1.5 er). Control experiments clarified that a bulky tert-butyl group and phosphonium and thiourea moieties were necessary to achieve such high stereoselectivity
Making kinetic and thermodynamic enolates via solvent-free high speed ball milling
作者:Daniel C. Waddell、Indre Thiel、Tammara D. Clark、S. Tyler Marcum、James Mack
DOI:10.1039/b922108p
日期:——
solvent-free high speed ball milling conditions. Using 2-methylcyclohexanone as the substrate and sodium hydroxide or lithium hexamethyldisilazide as the base, we were able to trap the thermodynamic or kinetic enolate in high selectivity. Although all the reagents were ball milled simultaneously, we observed no products resulting from aldol condensation.
The present invention relates to chiral resins comprising the formula:
wherein R is selected from the group consisting of H, C
1
-C
6
alkyl and C
1
-C
6
branched alkyl; “n” represents an integer ranging from 1 to 3; and wherein “m” represents an integer ranging from 0 to 3.
Conducting moisture sensitive reactions under mechanochemical conditions
作者:Daniel C. Waddell、Tammara D. Clark、James Mack
DOI:10.1016/j.tetlet.2012.06.009
日期:2012.8
Dry organic solvents are used for various organic reactions that employ moisture sensitive reagents. The processes to dry these solvents are hazardous and costly. Setting up reactions in an open atmosphere while using moisture sensitive reagents has little to no effect on the rate or yield of the reaction under mechanochemical conditions. We believe this is partly due to the gaseous nature of the water vapor in the air compared to the dissolved water and oxygen in solution. (C) 2012 Elsevier Ltd. All rights reserved.