BROWN Acetylene Zipper Reaction

Negishi and Abramovitch have described an extremely elegant use of two generations of Brown chemistry in the four-step synthesis of the insect sex pheromone of the European grape vine moth Lobesia botrana, (7E,9Z)-dodeca-7,9-dien-l-yl acetate (101). The now familiar acetylene zipper reaction converts (102) into (103), the terminal acetylene (103) produced being then coupled via the borane (104) to give the ( )-dodec-7-en-9-yn-l-yl acetate (105) in >99% isomeric purity and in 70% yield. Hydroboration then leads to the desired product (Scheme 26). 

Procedure A. When the acetylene zipper reaction was complete, the dark-brown reaction mixture was poured into ice water and the mixture was shaken. The organic layer was separated, returned to the flask, then the coupling reaction was carried out as described below. 

In 1975 Brown and Yamashita reported that a triple bond in any position of a straight chain hydrocarbon or acetylenic alcohol, when treated with a sufficiently strong base, could be isomerized exclusively to the free terminus of the chain. The "zipper reaction" thus provides a general solution to the problem of remote functionalization of a long hydrocarbon chain. Isomer-izations along chains of thirty carbon atoms have been achieved. 

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