Enynes and Polyunsaturated Hydrocarbons

A useful application of the oxy-Cope rearrangement has been used to produce conjugated enynes [e.g. (114) - (115)]. The enyne (115) is an intermediate in a synthesis of the sex pheromone of the Pine Sawfly Neodiprion lecontei. Potassium t-butoxide in liquid ammonia has been found to be the preferred base to produce high yields of the conjugated 1-alkylthio- or l-arylthiobut-3-en-l-ynes (117). Elimination of thiols from the acetylenic disulphides (116) under these conditions completely suppresses the competing formation of cumulene or diene-sulphides. 

Two molar equivalents of homopropargylating agents, such as (118), couple in excellent yield with the cuprates (119) derived from terminal acetylenes, provided that hexamethylphosphoramide and trimethyl phosphite are present in the reaction medium. The coupled products (120) serve as useful precursors to insect pheromones.  

Reagents i, cyclo-octatetraene dibromide ii, hv iii, aqueous base 

A novel scheme to Vitamin D3 derivatives has been reported by Okamura and his co-workers. The key step in the sequence is the coupling of the cuprate 

Functionalization of the terminal double bond of polyisoprenoids is achieved by regioselective addition of benzenesulphenyl chloride followed by base-induced elimination of hydrogen chloride thus treatment of the benzyl ether (128) of E. E-farnesol gives the sulphide (129) in 48% yield.Trienes and 

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