Divinylcyclobutane

The Cope rearrangement is of great importance as a synthetic method e.g. for the construction of seven- and eight-membered carbocycles from 1,2-divinylcyclopropanes and 1,2-divinylcyclobutanes respectively (e.g. 11 12),... 

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... 

Not all Cope rearrangements proceed by the cyclic six-centered mechanism. Thus c/5-1,2-divinylcyclobutane (p. 1445) rearranges smoothly to 1,5-cycloocta-... 

The thermal isomerization of syn-2 has been studied in detail.68 When a solution of syn-2 in decahydronaphthalene was heated at 220 °C, it isomerized to anti-2 quantitatively (Scheme 15). When anti-2 in decahydronaphthalene was likewise heated at 220 °C, no isomerization of anti-2 to syn-2 was observed, and anti-2 was recovered. The thermolysis pathway is partially dilferent from that of the corresponding ladderane syn-tricyclo[4.2.0.02,5]octane was reported to give 1,5-cyclooctadienes, anti-tricyclo[4.2.0.02,5]octane, and 1,2-divinylcyclobutanes in 51, 41, and 8% yields, respectively.29c,d... 

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... 

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 cw-1,2-divinylcyclobutane (Eq. 15)), resulting in the formation... 

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

Another available stereoselective synthetic pathway, starting from ris-1,2-divinylcyclobutanes produced in the solid state, is that of ring expansion to 1,5-... 

Table 18. Cycloocta-1,5-dienes from Thermally Induced Rearrangement of 1,2-Divinylcyclobutanes...

Nickel(O) or palladium(II) compounds in stoichiometric amounts promote the ring enlargement of simple alkyl-substituted 1,2-divinylcyclobutanes in benzene at room temperature to give 1 1 metal complexes of cycloocta-1,5-dienes.119 Destruction of the palladium complexes with potassium cyanide affords the free cycloocta-1,5-dienes. The stereochemistry observed is the same as in the thermal reaction at 150°C. 

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... 

Cyclization of butadiene catalysed by Ni(0) catalysts proceeds via 7r-allylnickel complexes. At first, the metallacyclic bis-7i-allylnickel complex 6, in which Ni is bivalent, is formed by oxidative cyclization. The bis-7r-allyl complex 6 may also be represented by cr-allyl structures 7, 8 and 9. Reductive elimination of 7, 8 and 9 produces the cyclic dimers 1, 2 and 3 by [2+2], [2+4] and [4+4] cycloadditions. Selectivity for 1, 2 and 3 is controlled by phosphine ligands. The catalyst made of a 1 1 ratio of Ni and a phosphine ligand affords the cyclic dimers 1, 2 and 3. In particular, 1 and 3 are obtained selectively by using the bulky phosphite 11. 1,2-Divinylcyclobutane (1) can be isolated only at a low temperature, because it undergoes facile Cope rearrangement to form 1,5-COD on warming. Use of tricyclohexylpho-sphine produces 4-vinylcyclohexene (2) with high selectivity. 

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. 

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