Synthesis of Conjugated Z, -Dienes

Synthesis of symmetrical (Z, dienes may be performed by the following procedure (Eq, 80) 108). It has been suggested that the migration of an alkyl group proceeds with inversion at the migration terminus and deiodoboration occurs in a trans manner. 

Another method to symmetrical (Z, )-dienes is through dialkenylchloroboranes (Eq. 82) 107). 

The synthesis of unsymmetrical derivatives has been reported, which involves stepwise treatment of an alkenyldialkylborane with lithium alkynide followed by boron trifluoride. Protonolysis of the intermediate affords in a good yield the iso-merically pure unsymmetrical (Z, )-dicnc (Eq. 83) U1). 

Most recently, a new and general synthesis of conjugated alkadienes has been reported by the reaction of 1-alkenyldiorgarioboranes with 1-alkenyl halides in the presence of palladium catalysts and bases 142). According to this procedure, (Z, E)-alkadienes are readily obtained, as revealed in Eq, 84. 

Recently, dialkenylchloroboranes were reported to undergo methylcopper-induced coupling to produce symmetrical E, )-1,3-dienes in excellent yields and high stereochemical purity (Eq. 85) In this reaction, it is essential to utilize 3 molar 

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A general method for the stereospecific synthesis of conjugated ( , Z)-dienes has been reported and used to synthesize bombykol and its derivatives (Scheme 16). 

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