Alkeneboronic esters

Alkeneboronic esters and acids are also readily available, as in the addition of vinyl-magnesium chloride" to trimethyl borate below —50°C, followed by hydrolysis." ... 

Because alkeneboronic esters are available from the cis-mono addition of HB(OR)2 to alkynes, both internal and external compounds, a convenient route to isomerically pure... 

Lithiated pinacol trimethylsilylmethaneboronate (37) condenses with aldehydes and ketones with exclusive elimination of the silicon component to form alkeneboronic esters [e.g. (38)]. Interestingly, reactions with aldehydes give products mainly of Z-configuration. ... 

Boron-stabilized anions have again been put to use in C—C bond-forming processes, an example of which is provided by the reaction of the anion (74) with electrophiles. Alkyl halides give substituted boronic esters, whereas aldehydes are converted to predominantly ci5-alkeneboronic esters, in contrast to the condensation of diborylmethide ions with aldehydes (mainly trans-). A useful homologation of carbonyl compounds to aldehydes involves reaction with the anion (75), to give alkeneboronic esters (76), followed by oxidation. ... 

Organolead compounds sometimes act as electrophiles. Thus, ary Heads having acetoxy ligands coupled with organostannane nucleophiles with a palladium catalyst (Scheme 49). ° The same strategy was applied also to the coupling with arene- and alkeneboronic acid esters (Scheme 50). 

---