Propyne, allenes

The pyrolysis of pyrrole produces a variety of products hydrogen cyanide, propyne, allene, acetylene, c/ -crotonitrile, and allyl cyanide, among them. Lifshitz et al. hypothesized that pyrrole undergoes 1,2-bond (N—C) cleavage, then an internal H-atom transfer, to yield a radical intermediate that can isomerize to either c/ -crotonitrile or allyl cyanide, or dissociate to HCN and propyne.Bacskay et al. completed quantum chemical comparisons of the isoelectronic pyrrolyl and cyclopentadienyl radicals they hypothesized that pyrrolyl radical is formed via C—H bond scission in the intermediate pyrrolenine (2/f-pyrrole) rather than directly via N—H bond cleavage (Fig. 14). Mackie et al. explained a similar finding, postulating that it was the formation of pyrrolenine that dictated the rate at which pyrrole pyrolysis occurred. 

The reaction has been successfully extended to a propyne-allene mixture the corresponding A -isopropenylpyr-roles were isolated as mixtures (Scheme 45) <2000S1585>. 

The propyne-allene/KOH/DMSO system was successfully employed for direct isopropenylation of diverse azoles (Equation 42) <200081585, 2003RJ0408>. 

Synthesis of pyrroles from ketoximes using propyne (allene)... 

SYNONYMS mapp gas, methyl acetylene - allene mixture, methyl acetylene - propadi-ene mixture (stabilized), propadiene methyl acetylene, propyne - allene mixture, propyne - pro-padiene mixture. 

Synonyms/Trade Names MAPP gas. Methyl acetylene-allene mixture, Propadiene-methyl acetylene. Methyl acetylene-propadiene mixture (stabilized), Propyne-allene mixture, Propyne-propadiene mixture ... 

In contrast to propyne, allene hydroformylation presents a kinetic and thermodynamic preference for the anfi-Markovnikov insertion, as indicated by the lower activation free energy (20.1 vs. 33.5 kJ/mol) and the higher stability of the insertion product (—122.2 vs. -54.0 kJ/mol) for anfi-Markovnikov path with respect to Markovnikov path. In terms of these energy differences, a ratio of 98 2 for anti-Markovnikov to Markovnikov products is predicted kinetically. Furthermore, from... 

METHYL ACETYLENE-PROPADIENE MIXTURE MAPP gas. Methyl acctylcnc>allene mixture. Propyne-allene mixture Strong oxidizers, copper alloys (>67 Cu NA 3.4 11... 

The reaction temperature and time as well as structure of the starting propyne-allene mixture effect slightly on the ratio of pyrroles formed. Only a weak dependence of the regioisomers ratio upon the catalyst nature and propyne pressure (concentration) is observed. The reaction outcome strongly depends on ketoxime... 

The reaction of ethyl methyl ketoxime with propyne-allene mixture, despite the increased temperature (115°C-125°C), remains regioselective (only the methylene... 

Synthesis of pyrroles from ketones (through ketoximes) and propyne-allene mixture, a large-scale side product of hydrocarbons pyrolysis, essentially expands the preparative possibilities of the Trofimov reaction. 5-Methyl-substituted pyrroles, having diverse substituents in the positions 2 and 3, become readily available for the first time. 

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