Cis- 1,2-Divinylcyclobutanes

Similarly the conversion of cis 1, 2 divinylcyclobutane also involves a boat transition state. 

Not all Cope rearrangements proceed by the cyclic six-centered mechanism. Thus cis-1,2-divinylcyclobutane (p. 1131) rearranges smoothly to 1,5-cyclooctadiene, since the geometry is favorable. The trans isomer also gives this product, but the main product is 4-vinylcyclohexene (resulting from 8-33). This reaction can be rationalized as proceeding by... 

The Cope and oxy-Cope rearrangement are very useful in organic synthesis, particularly when the 1,5-diene system is incorporated in a ring, then intringuing cyclic compounds may result. Also, the Cope and oxy-Cope rearrangements are greatly facilitated for a cis-1,2-divinylcyclobutane (Eq. 15)), resulting in the formation... 

The cis-1,2-divinylcyclobutane in the reaction mixture rearranges rapidly under reflux to the higher-boiling 1,5-cyclo-octadiene. 

If cis-1,2-divinylcyclobutane is desired, it can be isolated in 7-8% yield from the reaction mixture by preparative gas chromatography with the Beckman Megachrom instrument, using columns packed with Apiezon J. 

Ozkan, I., Zora, M. Transition Structures, Energetics, and Secondary Kinetic Isotope Effects for Cope Rearrangements of cis-1,2-Divinylcyclobutane and cis-1,2-Divinylcyclopropane A DFT Study. J. Org. Chem. 2003, 68, 9635-9642. 

Tetrachloropalladate(II) ion catalyzes the interconversion of 1- and 2-butenes in aqueous solutions containing chloride and hydronium ions. Sodium tetrachloropalladate(II) catalyzes the conversion of allylbenzene to propenyl-benzene in acetic acid solutions. Tetrakis(ethylene))Lt,/x -dichlororhodium(l) catalyzes butene isomerization in methanolic hydrogen chloride solutions . Cyclooctadienes isomerize in benzene-methanol solutions of dichlorobis-(triphenylphosphine)platinum(11) and stannous chloride. Chloroplatinic acid-stannous chloride catalyzes the isomerization of pentenes. Coordination complexes of zero-valent nickel with tris(2-biphenylyl)phosphite or triphenyl-phosphine catalyze the isomerization of cis-1,2-divinylcyclobutane to a mixture of c/5,m-l, 5-cyclooctadiene and 4-vinylcyclohexene . Detailed discussions of reaction kinetics and mechanisms appear in the papers cited. 

The trans isomer of 1,2-divinylcyclobutane may be isolated in low yield from the mixture formed by thermal dimerization of butadiene.5 The cis isomer has been prepared by a sequence of reactions.6... 

Photolysis, apparatus for, 47, 65 of butadiene to cis- and Irans-1,2-divinylcyclobutane, 47, 65 of dispiro[5.1.5.l]tetradecane-7,14-dione to cyclohexylidenecyclo-hexane, 47, 34... 

Photochemical sensitizer. DeBoer, Turro, and Hammond1 selected Michler s ketone as sensitizer for the photochemical dimerization of butadiene to cis-and trans-1,2-divinylcyclobutane the m-isomer undergoes thermal rearrangement... 

Reactions of conjugated dienes can also occur through the triplet state generated by photosensitization. 1,3-Butadiene gives a mixture of cis- and trans-1,2-divinylcyclobutane (1) and 4-vinylcyclohexene (2). 

Thermal reactions of 1,2-divinylcyclobutanes have been reported by Berson and his colleagues, and again steric factors were found to have an inhibiting effect upon the Cope rearrangement of the cis-compounds. Thermolysis of... 

Von besonderer praparativer und theoretischer Bedeutung sind die Er-gebnisse der photosensibilisierten Dimerisation von 1,3-Dienen. Hier konkurrieren C4-Cyclodimerisation und C6-Cyclodimerisation (Diels-Alder-Typ). So bildet sich aus Butadien bei der photosensibilisierten Dimerisation neben cis- und trans-l,2-Divinylcyclobutan (Formeln 16 tmd 17) auch 4-Vinylcyclohexen (Formel 18) (134, 139). Isopren liefert... 

Fusion of a strained ring system to the 3,4 positions of a 1,5-hexadiene also activates the diene toward isomerization provided that the vie vinyl groups of the divinylcycloalkane are cis to one another. C/ -l,2-divinylcyclobutane isomerizes about a million times faster than 1,5-hexadiene, and all attempts to synthesize m-I,2-divinylcyclopropane yielded its isomerization product, 1,4-cycloheptadiene, instead . ... 

In the absence of added phosphorus ligands, the principal product (80-90%) is trans, trans, rran5-l,5,9-cyclododecatriene (ttt-CDT 49), with smaller amounts of trans, trans, cw-l,5,9-cyclododecatriene ttc-CDT 50), trans, cis, c/5-l,5,9-cyclododecatriene (tcc-CDT 51), 1,5-cyclooctadiene (COD 52), 4-vinylcyclohexene (VCH 53), and c/5-l,2-divinylcyclobutane (DVCB 54). With the addition of phosphorus ligands, especially bulky phosphites, COD can become 96% of the product, and the rate of butadiene consumption can be increased by a factor of 10 (at 80°). ... 

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