Cycloaddition Of Allenes Research Articles

Allene cycloadditions. Part II. Reaction of a dialkylallene with unsymmetrical fluoro-olefins: evidence for a two-step [2 + 2] cycloaddition

Thermal cycloaddition of chlorotrifluoroethylene and 1,1-dichlorodifluoroethylene to 3-methylbuta-1,2-diene gives mixtures of four 1 : 1 adducts, identified as the 3-halogeno-3-chloro-2,2-difluoro-1-isopropylidenecyclobutanes (Ib, c), the 3-halogeno-3-chloro-2,2-difluoro-4,4-dimethyl-1-methylenecyclobutanes (IIb, c), the 2-halogeno-2-chloro-3,3-difluoro-1-methyl-1-vinylcyclobutanes (IIIb, c), and the 2-halogeno-2-chloro-3,3-difluoro-1-isopropenylcyclobutanes (IVb, c)(where halogeno = Cl or F). The effect of temperature on the product distribution in the reactions of 3-methylbuta-1,2-diene with tetrafluoroethylene and with chlorotrifluoroethylene has been studied. The results are discussed in relation to a stepwise cycloaddition mechanism via an intermediate diradical.

Allene cycloadditions. Part I. Reaction of tetrafluoroethylene with allenic hydrocarbons

Thermal cycloaddition of tetrafluoroethylene to propadiene gives a methylenespiroheptane (IV), an octafluorooctalin (VI), and a dispirodecane (VII), in addition to the methylenecyclobutane (I) and the spiroheptane (II) reported previously. The fluoro-olefin reacts with 3-methylbuta-1,2-diene at 150° to give a 61 : 17 : 5 : 2 mixture of isomeric 1 : 1 adducts (IX—XII): the first two arise by [2 + 2] cycloaddition to each of the two allenic π-bonds, the less substituted of which reacts faster; the remaining two adducts arise by prior rearrangement of the allene to isoprene, which reacts mainly at the more substituted double bond to give 2,2,3,3-tetrafluoro-1-methyl-1-vinyl-cyclobutane (XI). Reaction of tetrafluoroethylene with tetramethylallene occurs only after rearrangement of the allene to 2,4-dimethylpenta-1,3-diene, which undergoes cycloaddition only at the less-substituted double bond to give 2,2,3,3-tetrafluoro-1-isobutenyl-1-methylcyclobutane (XVI): the effect of reactant ratio, reaction time, and reactor pretreatment have been investigated. The mechanism of the cycloadditions is discussed.

Die kinetik der allendimerisation, ein beitrag zum mechanismus

The reaction kinetics of the dimerization of some polyhalogenated allenes with the general formula Cl 2 CCCCIX (X = Cl, Br, C 6 H 5 , COOEt) and of tetrabromoallene was studied by an IR spectrophotometric method. The reaction was found to be of strictly second order kinetics. The activation parameters were determined and the experimental data and the influence of the substituents were discussed in terms of the accepted general theory of allene cycloaddition. All data are in agreement with a non-concerted two-step electrocyclic addition mechanism. Within the experimental limits no paramagnetic species like a diradical could be detected by the ESR-method during the dimerization reaction of tetrachloroallene. Finally, an attempt was made to explain the extreme thermal instability of all polyhalogenated allenic monomers.

The simultaneity of allene cycloadditions. The reaction of tetracyanoethyleneoxide with allene.

The simultaneity of allene cycloadditions. The reaction of tetracyanoethyleneoxide with allene.

Evidence for a concerted mechanism for allene cycloaddition

Evidence for a concerted mechanism for allene cycloaddition