Synthesis of Z -Disubstituted Olefins

The synthesis of Z-disubstituted double bond was accomplished by Zweifel. The Zweifel s (Z)-alkene synthesis involves the iodination of dialkylvinylboranes in the presence of sodium hydroxide which results in the transfer of an alkyl group from boron and the formation of the (Z)-alkene (Eq. 62) although the introduction 

The versatility of this reaction is further demonstrated by the fact that the alkyl groups on vinylic dialkylboranes migrate with retention of configuration (Eq. 64) thus, greatly extending the scope of this reaction. 

However, the utility of this Zweifel cw-olefin synthesis was severely handicapped in the past on account of the following difficulties  

Recently, a wide variety of dialkylboranes have been readily prepared in situ, via hydridation of dialkylhaloboranes . And the first diffidulty is overcome by carrying out the hydroboration of 1-alkynes with dialkylboranes at lower temperatures Fortunately, the second difficulty, the concmrent formation of alkyl 

However, this method has an obvious disadvantage one of the R group is wasted. The final solution to this problem has now been provided with dibromoborane-methyl sulfide (Eq. 67) 

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