Pyrazoles pyrolysis

Pyrazolo[3,4-c]pyrazole, tetrahydro-rearrangement, 5, 250 Pyrazolo[4,3-c]pyrazole, tetraaryl-electrophilic substitution, 6, 1035 oxidation, 6, 1034-1035 reduction, 6, 1035 vacuum pyrolysis, 6, 1035 Pyrazolo[ 1,2-n]pyrazole-1,5-diones synthesis, 6, 991 Pyrazolo[ 1,2-n]pyrazoles reactions, 6, 1038 ring opening, 6, 983... 

High-temperature gas-phase pyrolysis of pyrazole and indazole derivatives 99MI27. 

Pyrazolines (51) can be converted to cyclopropane and N2 on photolysis""" or pyroiysis. The tautomeric 2-pyrazolines (52), which are more stable than 51 also give the reaction, but in this case an acidic or basic catalyst is required, the function of which is to convert 52 to 51." In the absence of such catalysts, 52 do not react/ In a similar manner, triazolines (53) are converted to aziridines." Side reactions are frequent with both 51 and 53, and some substrates do not give the reaction at all. However, the reaction has proved synthetically useful in many cases. In general, photolysis gives better yields and fewer side reactions than pyrolysis with both 51 and 53. S/Z-Pyrazoles" " (54) are stable to heat, but in some cases can be converted to... 

Isolable pyrazolines (183) are obtained from the (1,3-butadiene)phosphonic acid esters (182 X=S02Me, COOalkyl R "=H or Me R2=Me or Ph) (products from (182 X=CN) are thermo-labile) and diazomethane. Pyrolysis of the phosphorylated pyrazolines affords phosphonopentadienes rather than phosphono-cyclopropanes (contrast (184)) and with NaH give pyrazoles or pyrazolephbsphonic acid esters. 

Reaction of the dicyanoindenone 231 with pyrazole or 1,2,3-triazole diazonium salts gives deeply colored amino-triazines 232 and 233, which cyclize upon pyrolysis to give the pentacyclic compounds 234 and 235 containing the pyrido[2,3-f]-l,2,4-triazine nucleus (Scheme 36) <2003JRM1161>. 

In the gas-phase pyrolysis of dihydro-3,3,5,5-tetramethyl-4-methylene-4,5-3/7-pyrazole (31), only l-isopropylidene-2,2-dimethylcyclopropane was found it is stable under the reaction conditions as the only product in addition to molecular nitrogen (90CB1161). If thermodynamic product control is assumed, which seems reasonable in view of the high temperature, then the exclusive observation of the non-least-motion product is readily explained in terms of the low equilibrium concentration of its isomer, which is below the limit of detection by PE spectroscopy. 

Pyrolysis of the quaternary salts of pyrazoles causes loss of alkyl halide and reformation of N-substituted pyrazoles. If the substituents in the 3- and 5-positions are similar in character, as well as those on the two nitrogen atoms, then the two possible products will be formed in comparable quantities.81 83,152, 412 711... 

R = R1 = Ph) in very high yield by photolysis, the pyrazole is formed in only 3 % yield from diphenylethyne.50) The formation of cyclopropenes from pyrazoles apparently occurs via the corresponding diazo-compound. Thus photolysis of (53, R = R1 = Ph) at between 330 and 410 nm has been shown to lead to the diazo-compound (56) which on further photolysis or pyrolysis is converted to (54)50). Indeed, photolysis of vinyldiazoalkanes provides a good route to cyclopropenes thus photolysis of E- (57) leads to 3-alkoxycarbonyl-3-cyanocyclopropene51), while (58) leads either to the corresponding cyclopropene or to reversal to the pyrazole5Z). 

PTV PU PVA PVAC PVAL PVC PVDC PVDF PVE PVF PXRD py Py PY Py-GC-MS pyr pyrr pz programmed-temperature vaporizer polyurethane poly (vinyl alcohol) poly(vinyl acetate) poly (vinyl alcohol) poly (vinyl chloride) poly(vinylidene dichloride) poly(vinylidene difluoride) poly (vinyl ether) poly(vinyl fluoride) powder X-ray diffraction pyridine (ligand) pyridine pyramidal (coordination compounds) pyrolysis-gas chromatography-mass spectrometry pyrazine (ligand) pyrrolidine (ligand) pyrazole (ligand)... 

G. I. Yranzo Flash vacuum pyrolysis of isoxazoles, pyrazoles and related compound 2004COR1071... 

Flash vacuum pyrolysis (FVP) reactions of pyrazole itself and DPP 63 were investigated in the presence of anionic clays having a hydrotalcite structure <2001JOG2943, 2002JOG8147>. Solid catalysts with Mg Al ratio equal to 2 1 containing carbonate, nitrate, and silicate as interlayer anions were employed. Between 400 and 600 °G, compound 1... 

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