Barbaralanes synthesis

Overall, this reaction has to be classified as a [l,2,(3)4,3]-elimination, because nitrogen is liberated from relative positions 1 and 3 (first and last figure), the 2/3-bond migrates to 3/4 (assistant figure = 3) in order to induce the substituent in 4 to migrate to 3. By complete analogy, the synthesis of barbaralane (268) from 267 (43 %)140), which has been formulated via a cation, has to be classified as [1,2,(3)4,1]-elimination, because both the 2/3-bond and the 4-H migrate. 

A number of important advances have been made to facilitate the synthesis of barbaralane (17) and related compounds. Ketone (249) is available in 19% yield by reaction of the dianion of cyclo-octatetraene with phosgene. Although methyl chloroformate fails to react with the dianion to give (249), other reactions shown in Scheme 35 proceed satisfactorily and reaction with... 

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