Direct Transacylation of 2,2,2-Trihaloethyl Esters with Amines and Alcohols Using Phosphorus(III) Reagents for Reductive Fragmentation and in Situ Activation
作者:Jeremy J. Hans、Russell W. Driver、Steven D. Burke
DOI:10.1021/jo991711m
日期:2000.4.1
reductants, with resultant carboxylate activation as an acyloxyphosphonium intermediate, and in situ trapping by amine or alcohol nucleophiles. Secondary and tertiary amides were synthesized, including a dipeptide, in good yields using hexamethylphosphorous triamide (Me2N)3P, as reducing agent. Optimal yields of esters derived from primary and secondary alcohols were obtained using tributylphosphine
Several pentaalkylguanidines have been prepared and found to be superior catalysts for the preparation of aryl and aralkylethers from carbonates and for the methylation of phenols with dimethylcarbonate. They also act as effective catalysts for esterification of acids with alkyl chloroformates but not for the acetylation of tertiary alcohols with acetic anhydride.
Effect of <i>ortho</i>
substituents on carbonyl carbon <sup>13</sup>
C NMR chemical shifts in substituted phenyl benzoates
作者:Vilve Nummert、Mare Piirsalu、Vahur Mäemets、Signe Vahur、Ilmar A. Koppel
DOI:10.1002/poc.1569
日期:2009.12
an upfield shift or shielding of the carbonylcarbon, while the electron‐donating substituents had an opposite effect. Because of the sterical consequences, ortho substituents revealed a deshielding effect on the 13C NMR chemicalshift of the carbonylcarbon. For all the meta‐ and para‐substituted esters, the reverse substituent‐induced inductive and resonance effects (ρI < 0, ρR < 0) were found to
记录了37种邻,间和对位取代的苯甲酸苯酯的13 C NMR光谱,这些苯甲酸在苯甲酰基和苯基部分中含有取代基,4个邻取代的甲基和5个乙基苯甲酸酯以及9个R取代的烷基苯甲酸酯。的影响邻上的羰基碳的取代基13 C NMR化学位移,δ CO,发现通过含有电感性的,线性多元回归方程来描述σ我,共振,σ ° - [R ,和位阻,ê,或υ取代基常数。对于所有的邻位含有取代基的酰基部分,以及所述苯基部分,所述取代基诱导的反向电感效应取代的酯(ρ我 <0),正常共振效应(ρ [R > 0),和负位阻效应(δ邻 <0)与Ë观察。在苯基部分有邻位取代基的情况下,共振效应可忽略不计。由于感应效应,邻位吸电子取代基表现出对羰基碳的高场移位或屏蔽,而给电子取代基具有相反的作用。由于空间上的后果,邻位取代基显示出对羰基碳的13 C NMR化学位移的屏蔽作用。对于所有的间位和对位取代的酯,反向取代基引起的电感和共振效应(ρ我 <0,ρ
Aerobic oxidation of NHC-catalysed aldehyde esterifications with alcohols: benzoin, not the Breslow intermediate, undergoes oxidation
作者:Eoghan G. Delany、Claire-Louise Fagan、Sivaji Gundala、Kirsten Zeitler、Stephen J. Connon
DOI:10.1039/c3cc42597e
日期:——
Benzoin (and neither the Breslow intermediate nor the NHC-aldehyde tetrahedral adduct) has been unambiguously identified as the oxidised species in aerobic NHC-catalysed aldehydeesterifications.
Abstract A new efficient and selectiveesterification reaction of carboxylic acids with chloroformates is described using silica-supported catalyst (PBGSiCl). The chemioselectivity of the reaction was high particularly for sterically hindered carboxylic acids supported by a single pathway reaction.