2-Benzylthio-8-amino(1,2,4)triazolo(1,5-a)pyridines

Abstract: The invention relates to 2-benzylthio-8-amino[1,2,4]triazolo[1,5-a]pyridines and a process for the preparation thereof. These compounds can be used for the preparation of 2-benzylthio[1,2,4]triazolo[1,5-a]pyridine compounds, which are important intermediates in the preparation of N-aryl[1,2,4]triazolo[1,5-a]pyridines. The reaction is generally carried out by combining one molar equivalent of a 2-benzylthio-8-chloro[1,2,4]triazolo[1,5-a]pyridine compound with at least 3 molar equivalents of stannous chloride, one molar equivalent of stannic chloride, and an excess of hydrogen chloride or at least one molar equivalent of the alcohol.

Description: The invention relates to 2-benzylthio-8-amino[1,2,4]triazolo[1,5-a]pyridines and a process for the preparation thereof. These compounds can be used for the preparation of 2-benzylthio [1,2,4] triazolo [1, 5-a] pyridine compounds, which are important intermediates in the preparation of N-aryl[1,2,4]triazolo[1,5-a]pyridines. The preparation of these N-aryl compounds from the amine compounds of the present invention is disclosed in European patent application 95 925587.8, of which the present application is a divisional application, and the contents of which are incorporated herein by reference. The 2-benzylthio[1,2,4]triazolo[1,5-a]pyridine compounds of the co-pending European application are useful as herbicides. The control of unwanted vegetation by means of chemical agents i.e. herbicides, is an important aspect of modern agriculture and land management. While many chemicals that are useful for the control of unwanted vegetation are known, new compounds that are more effective generally, are more effective for specific plant species, are less damaging to desirable vegetation, are safer to man or the environment, are less expensive to use, or have other advantageous attributes are desirable. A number of sulfonamide compounds, including certain substituted [1,2,4]triazolo[1,5-a]pyrimidine-2-sulfonamide compounds (U.S. Patent 4,954,163), and [1,2,4]triazolo[1,5-c]pyrimidine-2-sulfonamide compounds (U.S. Patent 5,010,195 and European Application 244.948) are known and are known to possess herbicidel activity, especially on broadleaf weeds. Certain N-aryl[1,2,4]triazolo[1,5-a]-pyridine-2-sulfonamide compounds are potent herbicides for the control of unwanted vegetation, have desirable crop selectivity, and have favorable toxicological and environmental attributes. These compounds have the following structure: wherein W represents Cl or (C 1 -C 3 )-alkoxy; X represents H; Y represents H, F, Cl, Br, I or CH 3 ; and Z represents hydrogen or a halogen atom. A number of these compounds can be prepared from the compounds of the invention described herein. The compounds of the invention can be used to prepare certain compounds usually in the form of a herbicidal composition containing one of more of them in admixture with an agriculturally acceptable adjuvant or carrier, which certain compounds exhibit strong herbicidal properties when applied either directly to the unwanted vegetation or to the locus thereof and when applied either preemergence or postemergence. The Chemical Abstracts nomenclature numbering system for [1,2,4]triazolo[1,5-a]pyridine ring compounds is as follows: The 2-benzylthio-8-amino[1,2,4]triazolo[1,5-a]pyridines, which can be obtained according to the present invention, have the chemical structure of Formula 1: wherein W represents Cl or (C 1 -C 3 )-alkoxy; X represents H; and Y represents H, F, Cl, Br, I or CH 3 . According to the invention, the compounds of Formula 1 are obtained by reducing a 2-benzylthio-8-nitro[1,2,4]triazolo[1,5-a]pyridine compound of Formula 2: wherein X represents H; and Y represents H, F, Cl, Br, I or CH 3 . In the art reaction procedures are known to reduce the nitro group in Formula 2, to obtain a compound of Formula 1. It has now been found, however, that the reduction of a compound of Formula 2 wherein X represents hydrogen, Y represents hydrogen, methyl, or a halogen (2-benzylthio-8-nitro[1,2,4]triazolo[1,5-a]pyridine and certain 7-substituted analogs) with stannous chloride in the presence of stannic chloride and a reactive medium comprising hydrogen chloride or a C 1 -C 3 alcohol produces not only the corresponding compound of Formula 1, but also the corresponding compound of Formula 1 wherein W represents chloro or alkoxy. The compound wherein W represents chloro or alkoxy can be made to be the dominate product. When the reactive medium contains hydrogen chloride as an essential ingredient, an 8-amino-2-benzylthio-5-chloro[1,2,4]triazolo[1,5-a]pyridine is obtained along with a small amount of an 8-amino-2-benzylthio[1,2,4]triazolo[1,5-a]pyridine compound. The reactive medium generally includes a solvent, which can be water, N-methyl-2-pyrrolidinone, N,N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, or an other suitable solvent. Concentrated aqueous hydrochloric acid is the generally preferred reactive medium according to the invention. When the reactive medium contains an alcohol as an essential ingredient, a 5-alkoxy-8-amino-2-benzylthio[1,2,4]triazolo[1,5-a]pyridine compound is obtained. Methanol, ethanol, and propanol are examples of suitable alcohols. The reaction is generally carried out by combining one molar equivalent of a 2-benzylthio-8-chloro[1,2,4]triazolo[1,5-a]pyridine compound with at least 3 molar equivalents of stannous chloride, one molar equivalent of stannic chloride, and an excess of hydrogen chloride or at least one molar equivalent of the alcohol. The alcohols are typically employed in a large excess. The reaction mixture is heated at 50 to 120°C with good agitation to effect the simultaneous reduction and substitution. The products can be recovered by standard means, including by dissolving the hydrochloride that is formed initially in water, basifying with an alkali metal hydroxide, and recovering the product by filtration or by solvent extraction. Compounds of Formula 2 can be prepared from (3 or 5)nitro-2-hydrazinopyridine compounds by consecutive reactions with carbon disulfide, hydrogen peroxide, and benzyl chloride and triethylamine. The reactions take place at ambient temperatures and are exothermic. A reaction period of up to several days is sometimes required to assure that all of the product is in the desired, rearranged state, but rearrangement takes place spontaneously under the reaction conditions. The method is similar to that disclosed in the art for the preparation of 2-benzylthio[1,2,4]triazolo[1,5-c]pyrimidine compounds. 2-Benzylthio[1,2,4]triazolo[1,5-c]pyrimidine compounds can be prepared by the reaction of 1-((1-imidazolylthionyl)amino)-2-iminopyridine compounds of Formula 3: with benzyl chloride in a solvent, such as butanol, by heating. The desired compounds of Formula 3 can be recovered by conventional means. Compounds of Formula 3 can be prepared by combining O-mesitylenesulfonylacetohydroxamate and perchloric acid in dioxane at temperatures below ambient, adding the solution obtained to 2-aminopyridine compounds of Formula 4: at temperatures below ambient, and then adding 1,1'-thiocarbonyldiimidazole to the mixture. The desired compounds of Formula 4 can be recovered by conventional means. It has additionally been found that compounds of Formula 2 can be prepared from the corresponding 2-amino[1,2,4]triazolo[1,5-a]pyridine of Formula 5: wherein W, X, Y, and Z are as defined for compounds of Formula 1. Compounds of Formula 5 wherein W represents OCH 2 CH 3 or OC 3 H 7 (i) are often preferred. The method is closely related to the chemistry disclosed in J. Chemical Society communications , 1980 756-757. The preparation is preferably carried out by adding an excess of t -butyl nitrite to a solution consisting of a compound of Formula 5 and dibenzyl disulfide in a compatible organic solvent, such as acetonitrile, and heating the combination to reflux until the evolution of gas subsides. The reaction is exothermic. The desired compounds of Formula 2 can be recovered by conventional means, such as by removing the volatile components of the product mixture by evaporation, and can be purified by conventional means, such as by column chromatography or recrystallization. Compounds of Formula 5 can be prepared by treatment of appropriately substituted N-(2-pyridinyl)-N-carboethoxy-thiourea compounds with hydroxylamine in a solvent such as ethanol and heating for a few hours. The hydroxylamine is typically generated by neutralization of the hydrochloride with a hindered tertiary amine, such as diisopropylethylamine, or an alkoxide, such as sodium ethoxide. The desired compounds of Formula 5 can be recovered by conventional means, such as by removal of the volatile components of the reaction mixture by evaporation, and can be purified by conventional means, such as by extraction with water and/or other solvents in which they are sparingly soluble. N-(2-Pyridinyl)-N-carboethoxythiourea compounds can be obtained by treatment of appropriately substituted 2-aminopyridine compounds with ethoxycarbonylisothiocyanate. Compounds of Formula 5 can also be prepared from 2-cyanoaminopyridine compounds by the methods disclosed in Monatshefte fur Chemie , 114 789-798 (1983). The substituted anilines and 3-, 4-, and 5-aminopyrazoles that are required as intermediates for the compounds of Formula 1 are known in the art or can be prepared by general methods known in the art. The substituted 3-aminopyridines and 3-aminoindazoles that are required as intermediates can be prepared by the methods presented herein, are known in the art, or can be prepared by general methods known in the art. While it is possible to utilize the 1,2,4-triazolo[1,5-a]-pyridine-2-sulfonamide compounds prepared from the compound of the invention directly as herbicides, it is preferable to use them in mixtures containing a herbicidally effective amount of the compound along with at least one agriculturally acceptable adjuvant or carrier. Suitable adjuvants or carriers should not be physotoxic to valuable crops, particularly at the concentrations employed in applying the compositions for selective weed control in the presence of crops, and should not react chemically with the herbicidal compounds obtainable from the compound of the invention or other composition ingredients. Such mixtures can be designed for application directly to weeds or their locus or can be concentrates or formulations which are normally diluted with additional carriers and adjuvants before application. They can be solids, such as, for example, dusts, granules, water dispersible granules, or wettable powders, or liquids, such as, for example, emulsifiable concentrates, solutions, emulsions or suspensions. Suitable agricultural adjuvants and carriers that are useful in preparing the herbicidal mixtures of the invention are well known to those skilled in the art. Liquid carriers that can be employed include water, toluene, xylene, petroleum naphtha, crop oil, acetone, methyl ethyle ketone, cyclohexanone, trichloroethylene, perchloroethylene, ethyl acetate, amyl acetate, butyl acetate, propylene glycol monoethyl ether and diethylene glycol monomethyl ether, methanol, ethanol, isopropanol, amYl alcohol, ethylene glycol, propylene glycol, and glycerine. Water is generally the carrier of choice for the dilution of concentrates. Suitable solid carriers include talc, pyrophyllite clay, silica, attapulgus clay, kieselguhr, chalk, diatomaceous earth, lime, calcium carbonate, bentonite clay, Fuller's earth, cotton seed hulls, wheat flour, soybean flour, pumice, wood flour, walnut shell flour, and lignin. It is frequently desirable to incorporate one or more surface-active agents into the compositions of the present invention. Such surface-active agents are advantageously employed in both solid and liquid compositions, especially those designed to be diluted with carrier before application. The surface-active agents can be anionic, cationic or nonionic in character and can be employed as emulsifying agents, wetting agents, suspending agents, or for other purposes. Typical surface active agents include salts of alkyl sulfates, such as diethanolammonium lauryl sulfate; alkylarysulfonate salts, such as calcium dodecylbenzenesulfonate; alkylphenol-alkylene oxide addition products, such as nonylphenol-C 18 ethoxylate; alcohol-alkylene oxide addition products, such as tridecyl alcohol-C 16 ethoxylate; soaps, such as sodium stearate; alkylnaphthalenesulfonate salts, such as sodium dibutylnaphthalenesulfonate; dialkyl esters of sulfosuccinate salts, such as sodium di(2-ethylhexyl) sulfosuccinate; sorbitol esters, such as sorbitol oleate; quaternary amines, such as lauryl trimethylammonium chloride; polyethylene glycol esters of fatty acids, such as polyethylene glycol stearate; block copolymers of ethylene oxide and propylene oxide; and salts of mono and dialkyl phosphate esters. Other adjuvants commonly utilized in agricultural compositions include antifoam agents, compatibilizing agents, sequestering agents, neutralizing agents and buffers, corrosion inhibitors, dyes, odorants, penetration aids, spreading agents, sticking agents, dispersing agents, thickening agents, freeze point depressants, and antimicrobial agents. The compositions can also contain other compatible components, for example, other herbicides, plant growth regulants, fungicides, insecticides, and the like and can be formulated with liquid fertilizers of solid, particulate fertilizer carriers such as ammonium nitrate, and urea. The concentration of the active ingredients in the herbicidal compositions obtainable through this invention is generally from 0.001 to 98 percent by weight. Concentrations from 0.01 to 90 percent by weight are often employed. In compositions designed to be employed as concentrates, the active ingredient is generally present in a concentration from 5 to 98 weight percent, preferably 10 to 90 weight percent. Such compositions are typically diluted with an inert carrier, such as water, before application. The diluted compositions usually applied to weeds or the locus of weeds generally contain 0.001 to 5 weight percent active ingredient and preferably contain about 0.01 to 0.5 percent. These compositions can be applied to weeds or their locus by the use of conventional ground or aerial dusters, sprayers, and granule applicators, by addition to irrigation water, and by other conventional means known to those skilled in the art. The compounds prepared from the compound of the invention have been found to be useful preemergence and postemergence herbicides. They can be employed at non-selective (higher) rates of application to control essentially all of the vegetation in an area and, often, at selective (lower) rates of application for the selective control of undesirable vegetation in grass crops, such as corn, wheat, barley, and rice as well as in broadleaf crops, such as soybeans and cotton. While each of these compounds is within the scope of the invention, the degree of herbicidal activity, the selectivity, and the spectrum of weed control obtained varies depending upon the substituents present. The selection of a specific compound of the invention for a specific application can be done readily without invention from the data and information presented herein along with standard testing. The terms herbicide is used herein to mean an active ingredient which controls or adversely modifies the growth of plants. A herbicidally effective or vegetation controlling amount is an amount of active ingredient which causes an adversely modifying effect and includes deviations from natural development, killing, regulation, dessication, and retardation. The terms plants and vegetation are meant to include germinant seeds, emerging seedlings and established vegetation. Herbicidal activity is exhibited by the compounds of the present invention when they are applied directly to the plant or to the locus of the plant at any stage of growth or before emergence. The effect observed depends upon the plant species to be controlled, the stage of growth of the plant, the application parameters of dilution and spray drop size, the particle size of solid components, the environmental conditions at the time of use, the specific compound employed, the specific adjuvants and carriers employed, and the soil type, as well as the amount of chemical applied. These and other factors can be adjusted as is known in the art to promote selective herbicidal action. Generally, it is preferred to apply the compounds of Formula I postemergence to relatively immature plants to achieve the maximum control of broadleaf weeds. Application rates of 0.001 to 1 Kg/Ha are generally employed in postemergence operations; for preemergence applications, rates of 0.01 to 10 Kg/Ha are generally employed. The invention will be illustrated by the following examples. Example 1 Preparation of 8-Amino-2-benzylthio-5-chloro[1,2,4]triazolo[1,5-a]-pyridine by Reduction A mixture of 1.0 g (3.5 mmol) of 2-benzylthio-8-nitro[1,2,4]-triazolo[1,5-a]pyridine, 1.35 g (3.85 mmol) of stannic chloride pentahydrate, and 10 mL of concentrated hydrochloric acid was prepared and heated to 90°C with stirring. A solution of 1.99 g (10.5 mmol) of stannous chloride in 10 mL of concentrated aqueous hydrochloric acid was added slowly over a 1-hour period. After a short reaction period the mixture was allowed to cool and the solids present were collected by filtration. The collected solids were placed in water and the mixture was basified with dilute aqueous sodium hydroxide. The resulting mixture was extracted with dichloromethane and the organic extract was concentrated by evaporation under reduced pressure to obtain 0.60 g (66 percent of theory) of product as a brown solid. This solid was found to be 93 percent the title compound and 7 percent 8-amino-2-benzylthio[1,2,4]triazolo[1,5-a] pyridine by high pressure liquid chromatography. The pure compound melts at 113-114°C. Example 2 Preparation of 8-Amino-2-benzylthio-5-ethoxy[1,2,4]triazolo[1,5-a]pyridine by Reduction 2-Benzylthio-8-nitro[1,2,4]triazolo[1,5-a]pyridine (5.0 g, 0.017 mol) and stannic chloride pentahydrate (7.3 g, 0.021 mol) were mixed with 100 mL of ethanol and the mixture was heated to reflux with stirring. A solution of stannous chloride (13.2 g, 0.07 mol) in 100 mL of ethanol was added dropwise with stirring over 45 minutes and the heating was continued another 20 minutes after the addition was complete. The reaction mixture was diluted with dichloromethane. The resulting mixture was washed well with 2N aqueous hydrochloric acid and was then concentrated by evaporation under reduced pressure. The residue was chromatographed on silica gel eluting first with 5 percent ethyl acetate in dichloromethane and gradually increasing to 20 percent ethyl acetate in dichloromethane. The product fractions were concentrated by evaporation under reduced pressure and the residue was dissolved in dichloromethane. The resulting solution was washed well with 2N aqueous sodium hydroxide, dried over magnesium sulfate, and concentrated by evaporation under reduced pressure. The residue was mixed with hexane and the insoluble solids were recovered by filtration and dried to obtain 1.7 g (33 percent of theory) of the title compound as a dark tan powder melting at 106-107°C. Elemental Analysis C 15 H 16 N 4 OS Calc. %C, 60.0; %H, 5.37; %N, 18.7; %S, 10.7 Found %C, 59.8; %H, 5.49; %N, 18.8; %S, 10.5 Example 3 Preparation of 2-Benzylthio-5,8-dichloro[1,2,4]triazolo[1,5-a]pyridine A mixture of 9.9 g (0.10 mol) of copper(I) chloride with 300 mL of acetonitrile was prepared and 8,7 mL (6.8 g, 0.066 mol) of 90 percent t -butyl nitrite was added with stirring. After 10 minutes 9.5 g (0.033 mol) of 8-amino-2-benzylthio-5-chloro[1,2,4]triazolo[1,5-a]pyridine was added and the reaction mixture was allowed to react with stirring for 3 days. The mixture was then diluted with dichloromethane and 2N aqueous hydrochloric acid, and after mixing this well, the phases were separated. The organic layer was washed with 2N aqueous hydrochloric acid and concentrated by evaporation under reduced pressure. The residue was chromatographed on silica gel eluting with dicholoromethane to obtain 6.5 g (63 percent of theory) of the title compound as a yellow powder melting at 103-104°C. Elemental Ananoysis C 13 H 9 Cl 2 N 3 S Calc. %C, 50.3; %H, 2.92; %N, 13.6; %S, 10.3 Found %C, 50.4; %H, 3.08; %N, 13.6; %S, 10.3 2-Benzylthio-8-chloro[1,2,4]triazolo[1,5-a]pyridine was prepared similarly from 8-amino-2-benzylthio[1,2,4]triazolo[1,5-a]pyridine. A 65 percent yield of this compound was obtained as a yellow powder melting at 82-83°C. Elemental Analysis C 13 H 10 ClN 3 S Calc. %C, 56.6; %H, 3.66; %N, 15.2; %S, 11.6 Found %C, 56.6; %H, 3.33; %N, 15.3; %S, 11.5 Example 4 Preparation of 2-Benzylthio-8-bromo-5-chloro[1,2,4]-triazolo[1,5-a]pyridine Copper (I) bromide (4,9 g., 0034 mol) was combined with 200 mL of acetonitrile for 15 minutes and then 3.0 mL (2.3 g, 0.0023 mol) of 90 percent t -butyl nitrite was added and the mixture was stirred for a few minutes. 8-Amino-2benzylthio-5-chloro[1,2,4]triazolo[1,5-a]pyridine (3.3 g., 0.0013 mol) was then added and the resulting mixture was stirred for 2 days. The resulting mixture was concentrated by evaporation under reduced pressure and the residue was chromatographed on silica gel eluting with dichloromethane. After the solvent of the product fractions was removed by evaporation under reduced pressure, the residue was mixed with hexane and the solid material was recovered by filtration and dried to obtain 2.6 g (56 percent of theory) of the title compound as a yellow powder melting at 122-124°C. Elemental Analysis C 13 H 9 BrClN 3 S Calc. %C, 44.0; %H, 2.56; %N, 11.9; %S, 9.04 Found %C, 43.9; %H, 2.59; %N, 11.9; %S, 8.86

Claims: Process for the preparation of an amino compound of the formula: wherein W represents Cl or (C 1 -C 3 )-alkoxy; X represents H; and Y represents H, F, Cl, Br, I or CH 3 which process is characterized by reducing the corresponding nitro compound of the formula: wherein X represents H; and Y represents H, F, Cl, Br, I or CH 3 with stannous chloride at a temperature of about 50°C to about 120°C with good agitation in the presence of a reactive medium comprising stannic chloride and either hydrogen chloride or a C 1 -C 3 alcohol and, thereafter, basifying the product obtained to obtain said amino compound wherein W represents Cl or (C 1 -C 3 )-alkoxy respectively. Amino compound of the formula: wherein W represents Cl or (C 1 -C 3 )-alkoxy; X represents H; and Y represents H, F, Cl, Br, I or CH 3 . Use of the compound of claim 2 to prepare a benzylthio compound of the Formula: wherein W, X and Y are as defined in claim 2, and wherein Z is hydrogen or a halogen atom.

Inventors: ARNDT KIM E, ASH MARY LYNNE, BENKO ZOLTAN L, BRADLEY KIMBERLY BRUBAKER, COSTALES MARK J, EHR ROBERT J, JACHETTA JOHN J, KLESCHICK WILLIAM A, REIFSCHNEIDER WALTER, VAN HEERTUM JOHN C, ARNDT, KIM E., ASH, MARY LYNNE, BENKO, ZOLTAN L., BRADLEY, KIMBERLY BRUBAKER, COSTALES, MARK J., EHR, ROBERT J., JACHETTA, JOHN J., KLESCHICK, WILLIAM A., REIFSCHNEIDER, WALTER, VAN HEERTUM, JOHN C.
Applicants: DOW AGROSCIENCES LLC
Application year: 1995
Main classification: C07D471
IPC codes: A01N43, C07D471