Cyclic phosphonium salts are versatile reagents for the synthesis of unsymetrical unconjugated dienes,'S2 because their Wittig reactions provide alkenylphosphine oxides which can be subjected to further alkenation by the Horner-Wittig reaction. Applications of these tandem Wittig reactions include syntheses of insect sex pheromone~,~ 1, 4- diketone~,~ cycloheptenyldiphenylphosphine oxide derivative^^,^ and hydroazulenes. 6 ...
