Design of catalyst systems for the one-pot synthesis of menthols from citral

Trasarti, Andrés Fernando; Marchi, Alberto J.; Apesteguı́a, C.R.

doi:10.1016/j.jcat.2007.01.016

Cited by 63 publications

(61 citation statements)

References 42 publications

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“…[3][4][5][6][7][8][9][10] For instance, zinc bromide is used as a catalyst for this cyclisation in an industry process, which provides 2a with 92% of diastereomeric purity. Hence, a variety of methods has been reported for the diastereoselective cyclisation of citronellal to isopulegol.…”

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confidence: 99%

Highly selective aluminium-catalysed intramolecular Prins reaction for l-menthol synthesis

et al. 2014

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An aluminium complex bearing 2-cyclohexyl-6-phenylphenol afforded (5R)-n-isopulegol from (R)-citronellal via the intermolecular Prins reaction with an exceptionally high diastereoselectivity. Using this reaction, L-menthol was obtained with an excellent diastereoselectivity.Intermolecular and intramolecular ene reactions, especially the Prins reaction between carbonyl and olen compounds with Lewis or Brønsted acids, have received great attention. 1 A common application of the Prins reaction is the synthesis of (5R)-isopulegols (2) from (R)-citronellal ((R)-1) (Scheme 1).These are valuable intermediates for the synthesis of Lmenthol (3), one of the most popular fragrances in the world; 2 notably, only (5R)-n-isopulegol (2a) leads to the formation of (3). Hence, a variety of methods has been reported for the diastereoselective cyclisation of citronellal to isopulegol. 3-10 For instance, zinc bromide is used as a catalyst for this cyclisation in an industry process, which provides 2a with 92% of diastereomeric purity. 4a In addition, various other aluminium complexes have been recently proposed as only catalysts that afford (5R)isopulegols with a high diastereoselectivity. 11-14 For instance, tris(2,6-diphenylphenoxy)aluminium complex (ATPH, 4a), 14 which was prepared from triethylaluminium and 2,6-diphenylphenol (5a), has been used to carry out the Prins reaction of citronellal with a diastereoselectivity larger than 99% and 94% selectivity of 2 at 0 C. 11 However, 4a shows the excellent performance in a narrow temperature range. So, it's demanded a catalyst that provides higher reactivity and same diastereoselectivity, in order to apply it to a variety of industrial processes. In this work, we present aluminium catalysts with unprecedented excellent diastereoselectivity for the citronellal cyclisation.Firstly, we prepared tris(2-cyclohexyl-6-phenylphenoxy) aluminium complex (ACPP, 4b) with triethylaluminium and 2cyclohexyl-6-phenylphenol (5b). (R)-Citronellal ((R)-1) gave (5R)n-isopulegol (2a) in the presence of ACPP with 78% conversion, 95% selectivity of (5R)-isopulegols (2) and diastereoselectivity larger than 99% at À20 C while ATPH (4a) afforded 2a with 54% conversion (Scheme 2). A catalyst with such an excellent selectivity and reactivity has never been reported.We next investigated the reactivity of ACPP with a variety of reaction conditions. In particular, 3 mol% of ACPP afforded Scheme 1 Synthesis of L-menthol (3) from (R)-citronellal (1).

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Highly selective aluminium-catalysed intramolecular Prins reaction for l-menthol synthesis

et al. 2014

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“…a Determined at the end of the reaction. [30,31] showed that Cu exhibits poor activity for hydrogenating isolated C C bonds of ␣,␤-unsaturated compounds, which is a desirable metal property in our case for selectively obtaining unsaturated primary amines from unsaturated nitriles hydrogenation.…”

Section: Catalyst Activity and Selectivitymentioning

confidence: 90%

Chemoselective hydrogenation of unsaturated nitriles to unsaturated primary amines: Conversion of cinnamonitrile on metal-supported catalysts

Segobia

Trasarti

Apesteguı́a

2015

Applied Catalysis A: General

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“…This result seems to show that, compared to the mesoporous catalyst in scCO 2 , the deactivation process is faster for a conventional catalyst in an organic solvent medium. [27,28] …”

Section: Effect Of Amount Of Citralmentioning

confidence: 99%

Density‐Dependent Formation of the Pure trans‐Isomer of the Unsaturated Alcohol by Selective Hydrogenation of Citral in Supercritical Carbon Dioxide

et al. 2008

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Selective hydrogenation of citral to unsaturated alcohol [geraniol (trans) + nerol (cis)] was carried out in supercritical carbon dioxide (scCO 2 ) using an MCM-41 supported plantinum catalyst (1 wt% Pt). A remarkable rate of isomerization of the unsaturated alcohol [nerol (cis) to geraniol (trans)] during the hydrogenation of citral was achieved simply by tuning the density of CO 2 . Optimum reaction conditions were developed to obtain only geraniol (trans) with a selectivity of 98.8% and citral conversion of 99.8%. A significant change in the cis:trans ratio of the product (1:82.3) from the substrate (1:1.3) was observed depending on the various reaction parameters like carbon dioxide and hydrogen pressure, reactant concentration, reaction time and, particularly, the total selectivity for unsaturated alcohol [geraniol (trans) + nerol (cis)]. It has been observed that the presence of hydrogen is necessary for isomerization. Our results were explained in terms of a density-dependent, two-step model. The kinetic behaviour shows that the rate of isomerization was higher in scCO 2 compared to other organic solvents and the pure form of geraniol (trans) was obtained exclusively. A probable reaction pathway was proposed in order to explain the isomerization during hydrogenation of citral in scCO 2 medium.

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Design of catalyst systems for the one-pot synthesis of menthols from citral

Cited by 63 publications

References 42 publications

Highly selective aluminium-catalysed intramolecular Prins reaction for l-menthol synthesis

Highly selective aluminium-catalysed intramolecular Prins reaction for l-menthol synthesis

Chemoselective hydrogenation of unsaturated nitriles to unsaturated primary amines: Conversion of cinnamonitrile on metal-supported catalysts

Density‐Dependent Formation of the Pure trans‐Isomer of the Unsaturated Alcohol by Selective Hydrogenation of Citral in Supercritical Carbon Dioxide

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