AU606744B2 - Process for the preparation of 1-arylpyrazole-3-carboxylic acid esters - Google Patents
Process for the preparation of 1-arylpyrazole-3-carboxylic acid esters Download PDFInfo
- Publication number
- AU606744B2 AU606744B2 AU21818/88A AU2181888A AU606744B2 AU 606744 B2 AU606744 B2 AU 606744B2 AU 21818/88 A AU21818/88 A AU 21818/88A AU 2181888 A AU2181888 A AU 2181888A AU 606744 B2 AU606744 B2 AU 606744B2
- Authority
- AU
- Australia
- Prior art keywords
- denotes
- formula
- norbornadiene
- reaction
- alkyl
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Ceased
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D231/00—Heterocyclic compounds containing 1,2-diazole or hydrogenated 1,2-diazole rings
- C07D231/02—Heterocyclic compounds containing 1,2-diazole or hydrogenated 1,2-diazole rings not condensed with other rings
- C07D231/10—Heterocyclic compounds containing 1,2-diazole or hydrogenated 1,2-diazole rings not condensed with other rings having two or three double bonds between ring members or between ring members and non-ring members
- C07D231/14—Heterocyclic compounds containing 1,2-diazole or hydrogenated 1,2-diazole rings not condensed with other rings having two or three double bonds between ring members or between ring members and non-ring members with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Plural Heterocyclic Compounds (AREA)
Description
5) Signslure of APPIleflof (s) lof Se0o Company and -Signsitareaof Ats Giier.4a s prescribed by' its Articles of Association.
HOE.CHST .AKTIENGESEUSCH-AET D.B. MISCHLEWSKI -1 6 0 6 7 4 4.,M10 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-69 COMPLETE
SPECIFICATION
(ORIGINAL)
Class Application Number: Lodged: I t. Class Complete Specification Lodged: 000000Accepted: Priority: Published: 00% 0 0 Related Art: 0 00 Name of App! icant: Address of Applicant: 00 0 0 00 HOECHST AKTIENGESELLSCHAFT 45 Bruningstrasse, D-6230 Frankfurt Federal Republic of Germany.
/Main Actu,' Inventor: Address for Service ERICH SOHN and RUDOLF KUNSTMANN.
EDWD. WATERS SONS, 50 QUEEN STREET, MELBOURNE, AUSTRALIA, 3000.
Complete Specification for the invention entitled: PROCESS FOR THE PREPARATION OF 1-ARYLPYRAZOLE-3-CARBOXYLIC ACID ESTERS The following statement is a full description of this invention, including the best method of performing it known to S ^L I VL \yyyy PAT 510 Prokurist Authorized Signat ry ppa. Isenbruck i.V. Lapice I I la HOECHST AKTIENGESELLSCHAFT HOE 87/F 261 Dr.AU/sk Description Process for the preparation of 1-arylpyrazole-3-carboxylic acid esters 1-Arylpyrazole-3-carboxylic acid esters of the formula I indicated below are highly effective safeners for herbicides (DE-A 3,633,840). The synthesis of these pyrazoles described therein is effected by a cyclization reaction 10 of phenylhydrazines with 4-ethoxy-2-oxobut-3-enoic acid 0 00 0o. esters. The desired 3-pyrazolecarboxylic acid ester is 0 produced in this reaction in the form of a mixture with ooo° the corresponding 5-pyrazoLecarboxyLic acid ester. An 00 involved separation of isomers is necessary as a result; 0. 15 the undesired by-product must then be disposed of. The o 9 process also exhibits considerable technical disadvantages.
0o°o It is also known that pyrazoles are accessible by 1,3- 0 00 o dipolar cycloaddition reactions. Thus phenylsydnones 0 a 0 °0 0 20 can be reacted with acetylenes to give pyrazoles (DE-A 1,261,125). Mixtures of isomers (of 3-pyrazoLecarboxylic and 4-pyrazolecarboxylic acid esters) are, however, also formed in this reaction.
oo c 00 0 0 0 The selective synthesis of 3-pyrazolecarboxylic acid esters has only been described by the following complicated, multi-stage route of synthesis: N-phenyl-C-acetylnitrilimine is cyclo-condensed with norbornadiene to give pyrazolinonorbornene and the product is then aromatized to give 3-acetylpyrazole and the latter is degraded to the acid by means of I2/NaOH ER. Huisgen et al., Chem. Ber.
101, 536 to 551, (1968)]. Esterification finally affords the desired product.
The disadvantages associated with carrying out the known processes are overcome by means of the process according to the invention for the preparation of
I-
-2- 3-pyrazolecarboxyLic acid esters.
It has been found, surprisingly, that in the reaction of N-phenyl-C-aLkoxycarbonyLnitritimines with norbornadiene the compounds of the formula I are obtained selectively and in high yields.
The present application therefore reLates to a process for the preparation of 1-arylpyrazole-3-carboxylic acid esters of the formula I 0 00 0 0 0 0 00 0 0 00000 N( 0 0 0 0
C-O-R
o 15 1 a oa i n w h i c h t h e 0 00 Xs indlependlently of one another denote halogen, (CC-C 6 0o000 alkyl, (C 1
-C
6 )-akoxy, halogeno-(C 1
-C
6 )-aLkyL or 0000 020 halogeno-(C1-C6)-akoxy, R denotes H or (C 1
-C
6 )-akyl and 0000 oo n an integer from 1 to which comprises reacting a chlorohydrazone of the formula
II
a 25 0 O4 X5
"C
with norbornadiene of the formula III.
The reaction of phenylalkoxycarbonynitrilimines with compounds containing electron-rich double bonds was already known: reaction with cyclic enamines (Fusco et at.
Gazz. Chim. Ital. 91 (1961) 1233 et seq.) or with bismorpholinoethane compounds (Synthesis 1976 684/685). Symmetrical ethene compounds only afforded small yields of the desired product in this reaction.
i It could, therefore, also not have been expected that N-phenyL-C-alkoxycarbonyLnitrilimines would react in excellent yields with compounds which, Like norbornadiene, possess non-polarized, electron-deficient double bonds.
The process according to the invention is preferably used for the preparation of compounds of the formula I in which R denotes (C 1
-C
4 )-aLkyL, X denotes halogen, C 1 -halogenoalkyl or C 1 -halogenoalkoxy and n denotes 1 to 3.
Halogenoalkyl or halogenoalkoxy radicals are to be undero oo 0 stood as meaning especially the radicals -CF 3 and -OCF 3 0 0 oo The components of the formulae II and III can be reacted without a solvent, but can preferably be reacted in an inert organic solvent such as, for example, benzene, oo° toluene, xylene, chlorobenzene, monoethylene, diethylene or triethylene glycol ether, dimethylformamide, dimethyl o0o.o sulfoxida, N-methylpyrrolidone or pyridine.
S0 0 00 The process is advantageously carried out in the presence o of an organic or inorganic auxiliary base, such as, for 00 0 o a example, a trialkylamine, pyridine, an alkali metal carbonate or dicarbonate, alkaline earth metaL carbonate or o 0 25 dicarbonate, alkali metal hydroxide or alkali metal a 0 0 alcoholate.
It is advantageous to employ the base in excess, advantageously in up to 10 times the molar amount, relative to the compound II.
SIt is advantageous to employ norbornadiene in an excess Sof up to 20-fold, usually a 5-molar to 15-molar excess, relative to The process is carried out between 00 and 200 C. The intermediate product of the formula IV is formed initially in the reaction and this reacts further to give the end product on being heated further. If the reaction is carried out initially at relatively low 4 temperatures (00 to 80 0 the intermediate product of the formuLa IV can be isolated by adding a soLuble auxiliary base.
CIxn I CH 2
(IV)
N
COOR
Reaction temperatures from 600 to 200 0 C, preferably 700 to 1600C, are required for the subsequent cleavage of the intermediate product IV.
The chlorohydrazones of the formula II are accessible by customary processes. They can, for example, be obtained from the corresponding anilines by diazotization and coupling with 2-chloroacetoacetic acid esters.
The chlorohydrazones obtained in this synthesis can be used Ci 20 without prior purification, immediately after the addition of the solvent, for cyclocondensation with norbornadiene.
The following examples serve to illustrate the invention further.
':25 i 1. Preparation examples Example 1: Ethyl 1-(2,4-dichlorophenyL)-pyrazole-3-carboxyLate.
14.8 g (0.05 mol) of ethyl 2-chloroglyoxylate-2',4'dichlorophenylhydrazone (IIa) in 50 ml of toluene are stirred with 50 ml of norbornadiene and 20 ml of triethylamine for 1 hour at 700C. After cooling, the precipitate is filtered off with suction and rinsed with 20 ml of toluene, and the toluene phases are concentrated to dryness in a WV* The residue is subjected to gradient WV water pump vacuum 5 chromatography on silica geL (mobile phase: petroLeum ether to 700) changing to pure ethyl acetate). 14.5 g (82% of theory) of a colorless oil are obtained. This is identified by means of NMR spectroscopy. 3.5 g (0.01 mol) of the 1-(2,4-dichlorophenyl)-3-ethoxycarbonylpyrazolo- E2,2, 1]-bicyclo-heptene thus prepared are heated at 150 0
C
in WV for 3 hours, and, after cooling, the product is recrystallized from petroleum ether; this gives 2.6 g (88% of theory) of product, needles of melting point 88 to Example 2: Ethyl 1-(2,4-dichlorophenyl)-pyrazole 3-carboxylate 29.6 g (0.1 mol) of ethyl 2-chLoroglyoxylate-2',4'-dichlorophenylhydrazone (IIa) in 100 ml of toluene are stirred with 50 ml of norbornadiene and 40 ml of triethylamine for 1 hour at 70°C; after cooling, the precipitate is filtered off with suction and washed with 30 ml of toluene, and the combined toluene phases are evaporated in WV. The residue is heated at 1600C in WV for 3 hours and, after cooling, is taken up in 150 ml of ethyl acetate/100 ml of I I water, and the solution is washed with 100 ml of dilute i. hydrochloric acid, 100 ml of NaHCO 3 solution and 100 mL of water, dried over MgSO 4 and concentrated to dryness in WV.
Column chromatography gives 25.6 g (90% of theory) of the 25 desired product: crystals of melting point 88 to 90 0
C.
Example 3: EthyL 1-(2,4-dichlorophenyL)-pyrazole-3-carboxyLate 14.8 g of (IIa) in 100 ml of toluene are stirred with 50 ml of norbornadiene and 30 ml of pyridine at 100 0 C for 40 hour3. After cooling, the mixture is concentrated to dryness in WV and the residue is worked up as described under Example 2. This gives 4.3 g (30% of theory) of crystals of melting point 88 to 89 0
C.
Example 4: Methyl 1-(2,4-dichlorophenyl)-pyrazoLe-4-carboxyLate 14.6 g (0.05 mol) of methyl 2-chloroglyoxylate-2', ii 6 4'-dichlorophenylhydrazone in 100 ml of toluene are stirred with 50 mL of norbornadiene and 10 g of NaHC0 3 for 24 hours at 700C. After cooling, the mixture is worked up as described under Example 2: this gives 6.2 g (46% of theory) of crystals of melting point 105 to 107 0
C.
Example Ethyl 1-(2,4-dichlorophenyl)-pyrazole-3-carboxylate 5.9 g (0.020 mol) of IIa in 50 ml of DMF are stirred with 20 mL of norbornadiene and 5 g of NaHCO 3 for 0 CO 2 hours at room temperature; the resulting precipitate is filtered off with suction and rinsed with 20 ml of DMF.
o on The filtrate is concentrated to dryness in WV and the 0 b 00 015 resulting residue is heated at 160 C for 3 hours. Col- 00t.fl4 umn chromatography (petroleum ether (30 to 700) changing 0 0 0 o. to ethyl acetate on silica gel) gives 4.6 n (81% of theory) of crystals of melting point 88 to 90 C.
on o DMF dimethylformamide.
Example 6: o Ethyl 1-(2,4-dichlorophenyl)-pyrazole-3-carboxylate 5.9 g (0.02 mol) of IIa in 50 ml of DMF are stirred at 100 0 C for 8 hours with 20 ml of norbornadiene o °25 and 6 g of K 2 C0 3 After cooling, the precipitate is filtered off with suction and is rinsed with 20 ml of DMF.
The filtrate is concentrated to dryness in WV and the residue is chromatographed as described in Example This gives 2.1 g (37% of theory) of crystals of melting point 88 to 90 0
C.
Example 7: Ethyl 1-(2,4-dichlorophenyl)-pyrazole-3-carboxylate 5.9 g (0.02 mol) of IIa are stirred in 50 ml of DMF with 20 ml of norbornadiene for 40 hours at 1400C.
The mixture is concentrated to dryness in WV and the residue is chromatographed over silica gel. This gives 1.9 g (33% of theory) of crystals of melting point 88 to 90 0
C.
3 -7- Example 8: Ethyl 1-C2,4-di chLorophenyL )-pyrazoLe-3--carboxyLate 5.9 g (0.02 moL) of Ila in 40 mL of DMSO are stirred with 20 mL of norbornadiene and 6 g of KHCO 3 for 3 hours at room temperature and then for 3 hours at 1500 C.
The mixture is poured into 100 ml of water, and the precipitate is fiLtered off with suction. CoLumn chromatography of the filtrate gives 4.7 g (82% of theory) o: crystaLs of meLting point 88 to 900C.
The foLLowing esters of the formula I can be synthesized C 4 analogously.
440
COOR
Compound XnRm.P. yi n~gu~ 2 ExampLe Of Ryil to Example N No. %C No.
9 2,4-Br 2
C
2
H
5 103-5 68 1 4-0-n-C 4
H
9 -2-CF 3
C
2
H
5 oi L 78 2 11 4-CH 3 0 C 2
H
5 oi L 71. 1 4425 12 3- Cl-2 (C 2
H
5 2
C
2
H
5 i 6 13 4-F-3-CF 3
C
2
H
5 24-29 73 14 2-C1-4-CF 3
C
2
H
5 38-41 78 8 2,4-F 2 -3,5-CI 2
C
2
H
5 oiL 61 1 16 4-Cl-2-F-5-OCH 3
C
2
H
5 q 90-92 79 2 17 2,6-(C 2
H
5 2
C
2
H
5 oil 72 2 Example 18: 1-(2,4-DichtorophenyL )-pyrazoLe-3-carboxyL ic acid ml of norbornadiene and 10 g of KOH powder are added with cooling to 5.9 g (0.02 moL) of Ila in 100 ml of toLuene, and the mixture is stirred for 24 hours at room temperature. The organic phase is washed with 50 mL of dilute hydrochloric acid and is dried and concentrated to S-8dryness in WV. The resulting viscous oil is heated at 160 0 C in WV for 3 hours and, after cooling, the product is recrystallized from ethanol. This gives 3.2 g (62% of theory) of crystals of melting point 177 to 180 0
C.
I S S 00 4 0 0 0 0
Claims (8)
1. A process for the preparation of compounds of the formuLa I N C-O-R 0 1 d 0 0: 00 0 oo 0 0 00 oo 0 0 *D 00 0 o 0 0 00( in which the Xs independently of one another denote halogen, (C 1 C 6 )-aLkyl, (C 1 -C 6 )-aLkoxy, halogeno-(Cl-C 6 alkyl or halogeno-(CI-C 6 )-alkoxy, R denotes H or (C 1 -C 6 )-aLkyL and n denotes an integer from 1 to which comprises reacting a chLorohydrazone of the formula II x C. NH-N=C-C=O OR SII) (E11) with norbornadiene of the formula III
2. The process as claimed in claim 1, wherein, in formula II, R denotes (C 1 -C 4 )-alkyL, X denotes halogen, C 1 halogenoalkyL or C 1 -halogenoalkoxy and n denotes 1, 2 or 3.
3. The process as claimed in claim 1 or 2, wherein the reaction is carried out in an inert organic solvent.
4. The process as claimed in one of claims 1 to 3, wherein the reaction is carried out in the presence of an organic or inorganic auxiliary base.
The process as claimed in one or more of claims 1 to 4, 10 wherein the reaction is carried out at temperatures between 00 and 200 0 C.
6. The process as claimed in one or more of claims 1 to 4, wherein the process is carried out first between 0° and 80 0 C and subsequently between 800C and 160 0 C.
7. The process as claimed in claim 4, 5 or 6, wherein the auxiliary base is employed in a molar to 10 times molar amount, relative to the component II. 0 a0
8. The process as claimed in one or more of claims 1 to 7, wherein norbornadiene is employed in a molar to o .o 20 times molar amount, relative to the component II. 0 0 0 ooo00 0 CO DATED THIS 1st day of September, 1988 o 00 oo0 S.HOECHST AKTIENGSELLSCHAFT '0 0 EDWD. WATERS SONS, o PATENT ATTORNEYS, 50 QUEEN STREET, MELBOURNE. VIC. 3000.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19873729598 DE3729598A1 (en) | 1987-09-04 | 1987-09-04 | METHOD FOR PRODUCING 1-ARYL-PYRAZOL-3-CARBONIC ACID ESTERS |
| DE3729598 | 1987-09-04 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| AU2181888A AU2181888A (en) | 1989-03-09 |
| AU606744B2 true AU606744B2 (en) | 1991-02-14 |
Family
ID=6335217
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| AU21818/88A Ceased AU606744B2 (en) | 1987-09-04 | 1988-09-02 | Process for the preparation of 1-arylpyrazole-3-carboxylic acid esters |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0307676A1 (en) |
| JP (1) | JPS6483070A (en) |
| AU (1) | AU606744B2 (en) |
| BR (1) | BR8804533A (en) |
| DE (1) | DE3729598A1 (en) |
| DK (1) | DK488088A (en) |
| HU (1) | HU201022B (en) |
| IL (1) | IL87651A0 (en) |
| ZA (1) | ZA886539B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2743473B2 (en) * | 1988-07-04 | 1998-04-22 | 日産化学工業株式会社 | Method for producing pyrazole carboxylic acids |
| DE4001600C1 (en) * | 1990-01-20 | 1991-03-07 | Hoechst Ag, 6230 Frankfurt, De | Pyrazole carboxylic acid derivs. prepn. - by reacting azo-carboxylic acid cpd. with an enol-ether and aromatising |
| CN111592493B (en) * | 2020-05-30 | 2021-11-09 | 上海赫腾精细化工有限公司 | Preparation method of mefenpyr-diethyl |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU7930887A (en) * | 1986-10-04 | 1988-04-14 | Hoechst Aktiengesellschaft | Phenylpyrazolecarboxylic acid derivatives, their preparation, and their use as plant-growth regulators and safeners |
| AU3137389A (en) * | 1988-03-17 | 1989-09-21 | Hoechst Aktiengesellschaft | Plant protection agents based on pyrazolecarboxylic acid derivatives |
-
1987
- 1987-09-04 DE DE19873729598 patent/DE3729598A1/en not_active Withdrawn
-
1988
- 1988-08-25 EP EP88113834A patent/EP0307676A1/en not_active Withdrawn
- 1988-09-01 JP JP63216456A patent/JPS6483070A/en active Pending
- 1988-09-01 IL IL87651A patent/IL87651A0/en unknown
- 1988-09-02 DK DK488088A patent/DK488088A/en not_active Application Discontinuation
- 1988-09-02 HU HU884544A patent/HU201022B/en unknown
- 1988-09-02 AU AU21818/88A patent/AU606744B2/en not_active Ceased
- 1988-09-02 ZA ZA886539A patent/ZA886539B/en unknown
- 1988-09-02 BR BR8804533A patent/BR8804533A/en unknown
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU7930887A (en) * | 1986-10-04 | 1988-04-14 | Hoechst Aktiengesellschaft | Phenylpyrazolecarboxylic acid derivatives, their preparation, and their use as plant-growth regulators and safeners |
| AU3137389A (en) * | 1988-03-17 | 1989-09-21 | Hoechst Aktiengesellschaft | Plant protection agents based on pyrazolecarboxylic acid derivatives |
Also Published As
| Publication number | Publication date |
|---|---|
| ZA886539B (en) | 1989-04-26 |
| BR8804533A (en) | 1989-04-04 |
| JPS6483070A (en) | 1989-03-28 |
| DK488088D0 (en) | 1988-09-02 |
| DK488088A (en) | 1989-03-05 |
| EP0307676A1 (en) | 1989-03-22 |
| DE3729598A1 (en) | 1989-03-16 |
| IL87651A0 (en) | 1989-02-28 |
| HU201022B (en) | 1990-09-28 |
| HUT48603A (en) | 1989-06-28 |
| AU2181888A (en) | 1989-03-09 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Grigg et al. | The synthesis of fused ring nitrogen heterocycles via regiospecific intramolecular Heck reactions | |
| SK283894B6 (en) | Process for preparing sildenafil | |
| CA2582141C (en) | Process for the preparation of pyrazoles | |
| EP0145895B1 (en) | Intermediates useful in the preparation of certain chiral hydantoins, including sorbinil | |
| CA2106642C (en) | Carbazolone derivatives and process for preparing the same | |
| AU606744B2 (en) | Process for the preparation of 1-arylpyrazole-3-carboxylic acid esters | |
| Suwiński et al. | Nitroimidazoles XVII. Nucleophilic amination or ring transformation in reactions of 1-aryl-4-nitroimidazoles with 4-amino-1, 2, 4-triazole or hydroxylamine | |
| JPH02188589A (en) | Production of tri-lower alkanoyloxyboron | |
| US4892958A (en) | Preparation of 5-amino-1-phenyl-4-nitropyrazoles | |
| US3910911A (en) | Production of quinazolinone compounds | |
| Li et al. | Utilization of hypervalent iodine in organic synthesis: A novel and facile two‐step protocol for the synthesis of new derivatives of 1H‐Imidazo [1, 2‐b] pyrazole by the cyclocondensation involving α‐Tosyloxyacetophenones | |
| RU1838309C (en) | Method of synthesis of quinazoline derivatives or their pharmaceutically acceptable acid-additive salts | |
| KR19990013890A (en) | Process for the preparation of 2-chloro-benzimidazole derivatives | |
| Broggini et al. | Dipolarophilic behaviour of the thiophene ring in intramolecular nitrile imine cycloadditions | |
| EP0863874A1 (en) | Process for preparing dioxoazabicyclohexanes | |
| KR100424341B1 (en) | A process for preparing 1-Methyl- indazole-3-carboxylic acid | |
| Batog et al. | Synthesis of (1, 2, 3-triazol-1-yl) furazans. 2. Reaction of azidofurazans with morpholinonitroethene | |
| GB2463318A (en) | Preparation of anthranilamide derivatives containing a pyridinylpyrazole moiety | |
| IE912005A1 (en) | "New process for the industrial preparation of 4-chloro 3-sulphamoyl-N-(2,3-dihydro-2-methyl-1H-indol-1- yl)- benzamide from 2,3-dihydro-2-methyl-1H-indole and hydrox ylamine-O-sulphonic acid" | |
| Abdel-Latif et al. | Heterocycle syntheses through ternary condensation of terephthalaldehyde with malononitrile and some nucleophiles | |
| TW200409762A (en) | Process for preparing 3, 4-dichloro-n-(2-cyanophenyl)-5-isothiazolecarboxamide | |
| US5959119A (en) | Process for preparing 3,5-dimethylisoxazole-4-sulphonyl chloride | |
| KR100566318B1 (en) | A process for preparing carbazolone derivatives | |
| JPH02255673A (en) | 4-aryloxy-1,3-benzodioxoles and production thereof | |
| Elghandour et al. | Studies with alkylheterocyclic carbonitriles: a novel synthetic route to several new annelated pyrazolo [5, 1-c]-1, 2, 4-triazine derivatives |