Isomerisation process

Abstract: Transformation of specified 4H-substituted-­ 1,2,4-triazoles into their 1H-substituted isomers by heating at a temperature of 150°C to 300°C in the presence of a base and, essentially, in the absence of a polar aprotic solvent.

Description: This invention relates to an isomerisation process and, more particularly, to a process for transforming a 4H-substituted-1,2,4-triazole into the isomeric 1H-substituted-1,2,4-triazole. A process for transforming a 4H-beta-hydroxyethyl-1,2,4-triazole derivative into its 1H-isomer is described in EP-A-0143384. The process requires the use of a polar aprotic solvent. According to the present invention there is provided a process for transforming a 4H-substituted-1,2,4-triazole of the general formula (I) : in which R¹ is C₁₋₆ alkyl, C₃₋₆ cycloalkyl, C₃₋₆ cycloalkyl(C₁₋₄)alkyl or optionally substituted phenyl, and R² is optionally substituted phenyl, into the isomeric 1H-substituted-1,2,4-triazole, which comprises heating the triazole of formula (I) at a temperature of from 150°C to 300°C in the presence of a base and, essentially, in the absence of a polar aprotic solvent. Substituents which may be present in phenyl groups or the phenyl moieties of benzyl groups include one or more of halogen (especially chlorine and fluorine), C₁₋₄ alkyl, trifluoromethyl, C₁₋₄ alkoxy, nitro and phenoxy. The base is conveniently an alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide, but other bases such as alkaline earth hydroxides and oxides and alkali metal carbonates may be used. Alkali metal alcoholates, tertiary alkylamines and the sodium salt of 1,2,4-triazole may also be used. The amount of base required should be enough to avoid an unduly slow reaction but there is no upper limit other than what is economical and practicable. The optimum amount can be readily determined by experiment and will depend on the particular base and reaction conditions employed. As an indication, when solid sodium hydroxide is the base, as little as 0.01 mol may be used for each mol of triazole substrate and typically 0.5 to 2 mol up to 25 mol or even 100 mol may be used for each mol of substrate. The isomerisation is carried out at a temperature of from 155°C to 300°C, preferably from 155°C to 220°C and usually from 160°C to 190°C. The precise temperature employed will depend inter alia on the nature of the base, whether a diluent is used, the ease of isomerisation and the degree of isomerisation required. It is necessary only to heat the compound of formula (I) in the presence of a base in the temperature range from 150°C to 300°C. However, if desired the compound of formula (I) may be suspended or dissolved in a suitable medium such as an organic diluent, provided that the organic diluent is not a polar aprotic solvent as defined in EP-A-0143384, and that it does not react adversely with the triazole derivative under the conditions of the process. The diluent will, therefore, normally be either non-polar or protophilic. Acidic solvents which react with the triazole derivative should be avoided. Suitable diluents include saturated hydrocarbons such as Isopar M (a mixture of C₁₄ and C₁₅ isoparaffins), polyglycols such as polyethylene glycol (MW 300) and cyclic amines such as 1,2,4-triazole or a salt thereof. In some cases a diluent may be disadvantageous, for example it may be detrimental to the yield of product obtained, and in a preferred aspect of the invention the process is carried out essentially in the absence of any organic diluent. It may, however, be helpful to have water present, for example 5 to 6 mol per mol of triazole substrate, especially when a solid alkali metal hydroxide base is used. When the sodium salt of 1,2,4-triazole is used as a base and prepared in situ using sodium hydroxide, water will be generated in any case. The isomerisation may be performed in the presence of the isomeric 1H-substituted-1,2,4-triazole, which generally being more thermodynamically stable than the 4H-substituted-1,2,4-triazole remains unchanged in the reaction mixture. Thus, the process is of especial value in converting the relatively minor proportion, generally around 20% and more usually 15%, or below, of the undesired 4H-substituted-1,2,4-triazole (which is formed during the preparation of a 1H-substituted-1,2,4-triazole by reaction between 1,2,4-triazole or a salt thereof and a compound of formula (II): in which R¹ and R² have the meanings given before and X is chlorine or bromine or an epoxide derivative of compound (II)) into the desired 1H-substituted-1,2,4-triazole. Moreover, triazolisation of compound (II) or its corresponding epoxide may be performed under the conditions of the present process and reaction continued until sufficient of any unwanted 4H-substituted-1,2,4-triazole has been converted to the 1H isomer. The process of the invention is of particular interest for compounds of formula (I) in which R¹ is n - or t - butyl or phenyl, and R² is phenyl or benzyl, the phenyl groups and the phenyl moiety of the benzyl group being optionally substituted with fluorine and/or chlorine in the 2- and/or 4-positions of the phenyl ring. The invention is illustrated by the following Examples in which precentages are by weight. EXAMPLE 1 Conversion of 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(4H-1,2,4-triazol-4-yl)ethanol into 1-(2-fluorophenyl)-1(4-fluorophenyl)-2-(1H-1,2,4-triazol-1-yl) ethanol a) A dry mixture (3.0g) of 1-(2-fluorophenyl)-1(4-fluorophenyl)-2-(4H-1,2,4-triazol-4-yl) ethanol (2.89g) and 1-(2-fluorophenyl)-1(4-fluorophenyl)-2-(1H-1,2,4-triazol-1-yl) ethanol (0.11g) was placed in a 100 ml round-bottomed flask fitted with a reflux condenser and stirrer. Solid sodium hydroxide (0.46g) and poly(ethylene glycol) 300 (12.6g) were added and the mixture heated to 175°C and maintained at this temperature for two hours. The product obtained was identified by HPLC analysis as a mixture of 1-(2-fluorophenyl)-1(4-fluorophenyl)-2-(1H-1,2,4-triazol-1-yl) ethanol (0.63g) and 1-(2-fluorophenyl)-1(4-fluorophenyl)-2-(4H-1,2,4-triazol-4-yl) ethanol (0.05g); a ratio of 1H-isomer to 4H-isomer of more than 12:1. The yield of the 1H-isomer from starting 4H-isomer was thus 18% (0.63-0.11/2.89 x 100) and the total yield of 1H- and 4H-isomers was 23% (0.63 + 0.05/3 x 100). b) The method of Example 1 (a) was repeated except that water (1g) was present and the reaction temperature was 174°C. The product obtained was identified by HPLC analysis as a mixture of 1H-isomer (0.69g) and 4H-isomer (0.11g); a ratio of more than 6:1. The yield of 1H-isomer from starting 4H-isomer was 20% (0.69-0.11/2.89 x 100) and the total yield of 1H- and 4H-isomers gas 27% (0.69 + 0.11/ 3 x 100). EXAMPLE 2 Conversion of 1-(2-fluorophenyl)-1(4-fluorophenyl)-2-(4H-1,2,4-triazol-4-yl) ethanol into 1-(2-fluorophenyl)-1(4-fluorophenyl)-2-(1H-1,2,4-triazol-1-yl) ethanol A dry mixture (2.3g) of 1-(2-fluorophenyl)-1(4-fluorophenyl)-2-(4H-1,2,4-triazol-4-yl) ethanol (2.21g) and 1-(2-fluorophenyl)-1(4-fluorophenyl)-2-(1H-1,2,4-triazol-1-yl) ethanol (0.09g) was placed in a 100 ml round bottomed flask fitted with a reflux condenser and stirrer. Solid sodium hydroxide (0.6g), Isopar M (8g) and water (0.7g) were added and the mixture heated to 200°C and maintained at this temperature for 1.5 hours. The product obtained was identified by HPLC analysis as a mixture of 1-(2-fluorophenyl)-1(4-fluorophenyl)-2 (1H-1,2,4-triazol-1-yl) ethanol (1.41g) and 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(4H-1,2,4-triazol-4-yl) ethanol (0.03g); a ratio of 1H-isomer to 4H-isomer of 49:1. The yield of 1H-isomer from starting 4H-isomer was thus 60% (1.41-0.09/2.21 x 100) and the total yield of 1H- and 4-isomers was 63% (1.41 + 0.03/2.3 x 100). EXAMPLE 3 Conversion of 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(4H-1,2,4-triazol-4-yl) ethanol into 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(1H-1,2,4-triazol-1-yl) ethanol from a mixture obtained from 1,2-epoxy-1-(2-fluorophenyl)-1-(4-fluorophenyl) ethane and 1,2,4-triazole in dimethyl formamide 1,2-epoxy-1-(2-fluorophenyl)-1-(4-fluorophenyl) ethane (445g) was reacted with 1,2,4-triazole (159g) in dimethyl formamide (1043g) and potassium carbonate (132g) at 95°C for 6 hours. The resulting mixture was cooled to 70°C, the inorganic material filtered off and the latter washed with additional dimethyl formamide (180g). The solution obtained (1718.4g) contained 1-(2-fluorophenyl)-1-(4-fluoro-phenyl)-2-(1H-1,2,4-triazol-1-yl) ethanol (474.5g), in 82.2% yield, and 1-(2-fluorophenyl)-1-(4-fluoro-phenyl)-2-(4H-1,2,4-triazol-4-yl) ethanol (72.9g), in 12.6% yield, equivalent to a total yield of the isomeric triazoles of 94.9% from epoxide by HPLC determination. a) An aliquot of the solution (100g), containing 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(1H-1,2,4-triazol-1-yl) ethanol (27.61g) and 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(4H-1,2,4-triazol-4-yl) ethanol (4.24g) was distilled under vacuum at 5 mm Hg to a bath temperature of 135°C to remove dimethylformamide (>99% by analysis of analogous material and recovered weight of distillate). Subsequently, under setting for reflux at atmospheric pressure, solid sodium hydroxide (0.3g) was added to the melt and the bath temperature raised to 190°C, giving an internal temperature of 176°C. The melt was stirred under these conditions for two hours before removing the heating bath and addition of methanol (180g). The solution was filtered to remove the inorganics and the latter washed twice with futher methanol (2 x 30g). Analysis of the resulting solution by HPLC was used to determine the levels of the isomeric triazoles. The results are shown in Table I. b) A further aliquot (100g) was treated in the manner of Example 1 (a), but the addition of 0.4g sodium hydroxide. The results are shown in Table I. c) A further aliquot (100g) was treated in the manner of Example 1 (a), but with the addition of 0.5g sodium hydroxide. The results are shown in Table I. d) A further aliquot (100g) was treated in the manner of Example 1 (a), but with the addition of 0.8g sodium hydroxide. The results are shown in Table I. e) A further aliquot (100g) was treated in the manner of Example 1 (a), but with the addition of 1.0g sodium hydroxide. The results are shown in Table I. f) A further aliquot (100g) was treated in the manner of Example 1 (a), but with the addition of 1.5g sodium hydroxide. The results are shown in Table I. EXAMPLE 4 Conversion of 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(4H-1,2,4-triazol-4-yl) ethanol into 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(1H-1,2,4-triazol-1-yl) ethanol in a melt containing 1,2,4-triazole To a mixture consisting of 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(4H-1,2,4-triazol-4-yl) ethanol (2.13g) and 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(1H-1,2,4-triazol-1-yl) ethanol (0.09g) was added water (0.7g), solid sodium hydroxide (6.0g), and 1,2,4-triazole (6.7g). This was stirred under reflux at a bath temperature of 200°C, internal temperature of 156°C, for two hours, cooled and then dissolved in methanol (90g). The resulting solution was filtered and the inorganic cake washed with further methanol (total 50g). The total solution was analysed by HPLC and found to contain 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(1H-1,2,4-triazol-1-yl) ethanol (0.92g) and 1-(2-fluorophenyl)-1-(4-fluorophenyl)-1-(4-fluorophenyl)-2-(4H-1,2,4-triazol-1-yl) ethanol (0.11g), an increase of 0.83g of 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(1H-1,2,4-triazol-1-yl) ethanol, equivalent to a 39% yield based on the initial content of 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(4H-1,2,4-triazol-1-yl) ethanol. EXAMPLE 5 Selective synthesis of 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(1H-1,2,4-triazol-1-yl) ethanol from 1,2-epoxy-1-(2-fluorophenyl)-1-(4-fluorophenyl) ethane in a melt containing 1,2,4-triazole 1,2-epoxy-1-(2-fluorophenyl)-1-(4-fluorophenyl) ethane (2.67g) was stirred with sodium hydroxide (5.60g) and 1,2,4-triazole (6.90g) at a bath temperature of 200°C, internal temperature 163-170°C, for 3 hours. The reaction mass was cooled and methanol (63g) added to dissolve the melt. The resulting solution was filtered and the inorganic cake washed with further methanol (total 50g). HPLC analysis of the total solution showed 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(1H-1,2,4-triazol-1-yl) ethanol (2.78g) and 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(4H-1,2,4-triazol-4-yl) ethanol (0.04g), equivalent to a yield of 1-(2-fluorophenyl)-1-(4-fluorophenyl)-2-(1H-1,2,4-triazol-1-yl) ethanol of 80% based on epoxide.

Claims: A process for transforming a 4H-substituted-1,2,4-triazole of the general formula (I) : in which R¹ is C₁₋₆ alkyl, C₃₋₆ cycloalkyl, C₃₋₆ cycloalkyl(C₁₋₄)alkyl or optionally substituted phenyl, and R² is optionally substituted phenyl, into the isomeric 1H-substituted-1,2,4-triazole, which comprises heating the triazole of formula (I) at a temperature of from 150°C to 300°C in the presence of a base and, essentially, in the absence of a polar aprotic solvent. A process according to claim 1 which is carried out essentially in the absence of an organic diluent. A process according to claim 1 or 2 in which the base is an alkali metal hydroxide. A process according to claim 3 in which the base is sodium hydroxide. A process according to any one of the preceding claims in which water is present. A process according to any one of the preceding claims in which there is present initially with the 4H-substituted-1,2,4-triazole an amount of the corresponding 1H-isomer. A process according to claim 6 in which the 4H-isomer forms 20% or less of the total amount of 4H-and 1H-isomer initially present. A process according to any one of the preceding claims in which the 4H-substituted-1,2,4-triazole has the formula :

Inventors: JONES RAYMOND VINCENT HEAVON, JONES, RAYMOND VINCENT HEAVON
Applicants: ZENECA LTD, ZENECA LIMITED
Application year: 1989
Main classification: C07D249
IPC codes: C07D521, C07D249