1.2- Divinylcyclobutane, preparation

If s-l,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. 

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... 

Essentially the same procedure may be used to produce mixtures of cyclodimers from isoprene,4 1,3-cyclopentadiene,4 and 1,3-cyclohexadiene.7 Separation of all products is somewhat difficult in most cases but has always been possible by preparative vapor phase chromatography. Despite the problems that may be involved in separation of desired products in some instances, photocyclization frequently is the method of choice for preparation of 1,2-dialkenylcyclobutanes if they can be made major products of photoreactions. Starting materials are readily available, and the preparations are easily carried out on the scale described. There is little doubt that the method is the best for preparation of 2ra s-l,2-divinylcyclobutane. 

Oxy-Cope rearrangements are popular in the divinylcyclobutane series, because several good methods of preparation of 2-vinylcyclobutanones are available. A number of these ketones, such as (105), can be... 

The ra s-tricyclo[3.1.0.02-4]hexane derivatives, prepared according Eq. 15, are easily isomerized by some Rh(I) catalysts to give tram-1,2- and 1,3-divinylcyclobutane derivatives 72) (Eq. 19). 

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