Beyer, Hans published the artcileThiazoles. XXIX. The condensation products of thiosemicarbazide with ethyl α-chloroacetoacetate and a novel ring contraction of 2-amino-5-methyl-6-carbethoxy-1,3,4-thiadiazine to 3-methyl-4-carbethoxy-5-aminopyrazole, Synthetic Route of 23286-70-6, the publication is Chemische Berichte (1956), 1652-8, database is CAplus.
On condensation of AcCHClCO2Et (I) with H2NNHCSNH2 (II), 4-methyl-5-carbethoxy-2-thiazolylhydrazine (III), MeC(:NNHCSNH2)CHClCO2Et (IV), or 3-amino-4-methyl-5-carbethoxy-2-thiazolone imide (V) is formed, depending upon the pH and temperature Refluxing 13.3 g. 1-acetylthiosemicarbazide and 8.5 g. NaOAc in 75 cc. absolute EtOH in a CO2 atm., adding dropwise within 15 min. 16.5 g. I in 25 cc. absolute EtOH, and refluxing the mixture another hr. yield 96% N’-acetyl-N-(4-methyl-5-carbethoxy-2-thiazolyl)hydrazine (VI), fine needles, m. 227°, which (12.2 g.), refluxed in 75 cc. absolute EtOH 1 hr. with 5.3 cc. concentrated HCl, gives 88% III.HCl, needles, m. 189-90°. III.HCl is also formed in 80% yield when 4.1 g. I in 3 cc. EtOH is added (15 min.) to 2.28 g. II in 20 cc. EtOH at 50° (free III, liberated with NaOAc, 100%, leaflets, m. 186°; di-Ac derivative, prepared by heating 2.01 g. III or 2.43 g. VI with 15 cc. Ac2O 20 min. on a water bath, 84%, needles, m. 198°; tri-Ac derivative, prepared by heating 2.01 g. III 15 min. in 10 cc. Ac2O containing 5 drops concentrated H2SO4, prisms, m. 131°; monoformyl derivative, prepared by refluxing 2.01 g. III 1 hr. with 10 cc. 98% HCO2H, 92%, fine needles, m. 205°). Boiling 2.01 g. III 15 min. in 25 cc. Me2CO yields 92% acetone (4-methyl-5-carbethoxy-2-thiazolyl)hydrazone, silky needles, m. 143°; PhCOMe derivative, 95%, m. 118°. Adding dropwise (1 hr.) 16.4 g. I to 9.1 g. II in 50 cc. 2N HCl at 0° yields 100% IV, also formed in 78% yield by mixing the 2 reagents in alc. solution without HCl; IV decompose on storage. Adding at 70° 9.5 g. IV to 60 cc. PrOH and bringing the mixture quickly to the boil give 74% 2-amino-5-methyl-6-carbethoxy-1,3,4-thiadiazine-HCl, decompose about 90° [free base (VII), liberated with saturated NaOAc solution, fine yellow needles, decompose above 80°; after 2-3 days it decompose with the formation of 3-methyl-4-carbethoxy-5-aminopyrazole (VIII)]. Heating VII or IV with the calculated amount of p-O2NC6H4CHO (IX) in EtOH yields 40% IX (4-methyl-5-carbethoxy-2-thiazolyl)hydrazone, yellow needles, m. 244°; BzH analog, pale yellow leaflets, m. 189°, is prepared by treating III.HCl in 2N HCl with BzH and NaOAc, or in 93% yield by condensation of equimolar amounts of III and BzH. Heating 7.2 g. VII.HCl in 50 cc. concentrated HCl 15-20 min. on a water bath and concentrating the filtered solution to 1/3 its volume yield 66% V.HCl, fine needles, m. 242-4° (decomposition), which is also formed in 43% yield when 8.2 g. I is added to 4.6 g. II in 30 cc. hot concentrated HCl and the solution concentrated to 0.5 its volume (free V, needles, m. 130°; di-Ac derivative, prisms, m. 107-8°). Adding 1.28 g. NaNO2 in H2O to 2.4 g. V.HCl in 25 cc. 2N HCl at 0° and pouring the ice-cooled solution into 1.2 g. PhNMe2 in dilute HCl give 2-(p-dimethylaminophenylazo)-4-methyl-5-carbethoxythiazole (X).HCl, deep blue crystals, from which NH4OH liberates the free X, red-brown leaflets, m. 205°; X is also obtained in 43% yield when 3.7 g. 2-amino-4-methyl-5-carbethoxythiazole is diazotized at 0° and the diazonium solution is treated with 2.4 g. PhNMe2. Refluxing 9.5 g. VII.HCl 1 hr. in 50 cc. 2N alc. HCl and filtering off the S formed yield 80% VIII.HCl, m. 187-9° [free base, leaflets containing 1 mole H2O, m. 69°, m. 113° (H2O-free); nitrate, prisms, m. 197-8° (decomposition); mono-Ac derivative, prisms, m. 91°]. Treating 4.1 g. VIII.HCl in 15 cc. H2O and 3 cc. concentrated HCl at 0° with 1.38 g. NaNO2 in 7 cc. H2O, pouring the diazonium solution into ice cold 30% H3PO2, keeping the mixture overnight at 0°, and adding saturated NaOAc solution give 3-methyl-4-carbethoxypyrazole-H2O, m. 46° (HCl salt, needles, sinters 145°, m. 160°). Diazotizing 2.5 g. VIII.HCl, adding the diazonium solution to 1.2 g. PhNMe2 in dilute HCl, and then adding NaOAc give 70% 3-methyl-4-carbethoxy-5-(p-dimethylaminophenylazo)pyrazole, stout orange prisms, m. 172°.
Chemische Berichte published new progress about 23286-70-6. 23286-70-6 belongs to pyrazoles-derivatives, auxiliary class Pyrazole,Amine,Ester, name is Ethyl 5-amino-3-methyl-1H-pyrazole-4-carboxylate, and the molecular formula is C7H11N3O2, Synthetic Route of 23286-70-6.
Referemce:
https://en.wikipedia.org/wiki/Pyrazole,
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