Synthesis of new (−)-menthylgermanium derivatives and its use in heterogeneous bimetallic catalysis

Faraoni, María Belén; Vetere, Virginia; Casella, Mónica Laura; Podestá, Julio C.

doi:10.1016/j.jorganchem.2011.07.011

Cited by 6 publications

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“…Menthyl Grignard reagent 1 is prepared in the usual way from menthyl chloride ( 2 ) and magnesium in etheric solution. , This chiral organometallic reagent is widely used to attach menthyl groups to electrophilic centers. Reactions have been described, e.g., with carbon dioxide, − formaldehyde, dichloromethane, PCl 3 , ,, PhPCl 2 , Ph 2 PCl, ,, GeCl 4 , SnCl 4 , or organotin chlorides. ,, The reagent has also been used in cross-coupling , or transmetalation reactions . The products tend to retain menthyl configuration, and the sequence from 2 via 1 to various substitution products ( Men - E ) has usually been assumed to proceed with retention of configuration in all steps (Scheme ).…”

Section: Introductionmentioning

confidence: 99%

Stereochemistry of the Menthyl Grignard Reagent: Generation, Composition, Dynamics, and Reactions with Electrophiles

et al. 2018

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Menthyl Grignard reagent 1 from either menthyl chloride (2) or neomenthyl chloride (3) consists of menthylmagnesium chloride (1a), neomenthylmagnesium chloride (1b), trans-p-menthane (4), 2-menthene (8), 3-menthene (9), and Wurtz coupling products including symmetrical bimenthyl 13. The diastereomeric ratio 1a/1b was determined in situ by 13 C NMR or after D 2 O quenching by 2 H NMR analysis. Hydrolysis of the C−Mg bond proceeds with retention of configuration at C-1. The kinetic ratio 1a/1b from Grignard reagent generation (dr 59:41 at 50 °C in THF) is close 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 (1b I ). The kinetics of epimerization for the menthyl/neomenthylmagnesium system was analyzed (ΔH ⧧ = 98.5 kJ/mol, ΔS ⧧ = −113 J/mol•K for 1b I → 1a I ). Reactions of 1 with phosphorus electrophiles proceed stereoconvergently at C-1 of 1a/b to give predominantly menthyl-configured substitution products: PCl 3 and 2 equiv of 1 give Men 2 PCl (6), which hydrolyzes to dimenthylphosphine P-oxide (7), whereas Ph 2 PCl with 1 equiv of 1 gave Pmenthyldiphenylphosphine oxide (27) after workup in air.

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