Stereochemistry of the Menthyl Grignard Reagent: Generation, Composition, Dynamics, and Reactions with Electrophiles
作者:Sebastian Koller、Julia Gatzka、Kit Ming Wong、Philipp J. Altmann、Alexander Pöthig、Lukas Hintermann
DOI:10.1021/acs.joc.8b02278
日期:2018.12.21
to the thermodynamic ratio (56:44 at 50 °C in THF). Carboxylation of 1 at −78 °C separates diastereomers 1a/b to give the anion of menthanecarboxylic acid (19) from 1a, which combines with unreactive 1b to give neomenthylmagnesium menthanecarboxylate (1bI). The kinetics of epimerization for the menthyl/neomenthylmagnesium system was analyzed (ΔH⧧ = 98.5 kJ/mol, ΔS⧧ = −113 J/mol·K for 1bI → 1aI). Reactions
薄荷酰氯(2)或新薄荷酰氯(3)的薄荷格利雅试剂1由薄荷基氯化镁(1a),新薄荷基氯化镁(1b),反-对-薄荷烷(4),2-薄荷烯(8),3-薄荷烯组成(9)和包括对称二甲基联苯的13的Wurtz偶联产品。非对映体比率1A / 1B用原位测定13 C NMR或d后2被O淬火21 H NMR分析。C–Mg键的水解会继续保持C-1的构型。Grignard试剂产生的动力学比1a / 1b(在50°C于THF中为dr 59:41)接近热力学比(在50°C在THF中为56:44)。1在-78°C的羧化作用将非对映异构体1a / b从1a分离出薄荷烷羧酸(19)阴离子,再与不活泼的1b结合,得到新薄荷脑薄荷基羧酸镁(1b I)。差向异构化的对薄荷/ neomenthylmagnesium系统的动力学分析(Δ ħ ⧧ = 98.5千焦/摩尔,Δ小号⧧对于1b I → 1a I= -113J / mol·K