Electrophilic Trapping of Alkenymetal Intermediates with Borates

1 Electrophilic Trapping of Alkenymetal Intermediates with Borates 

Alkenylboronic acids can be synthesized from reactive alkenylmetal species in a way similar to that described above for arylboronic acids (Section 1.3.1.1.1) [224]. Typically, alkenyl bromides or iodides are treated sequentially with n-Buli and a trialkylbo-rate (entry 1, Table 1.4). A nonpolar trienylboronic acid was synthesized using this approach [226]. As described in Section 1.2.2.2, small boronic adds tend to be highly soluble in water and may be difficult to isolate when made using the traditional approach involving an aqueous workup. In these cases, exemplified with the polymerization-prone ethyleneboronic acid synthesized from vinyknagnesium bromide, it has proved more convenient to isolate the product as a dibutyl ester by extraction of the addic aqueous phase with butanol [227]. Recently, aUcoxy-functionaHzed butadi-enyl- and styrenyl boronic esters were synthesized from a,P-unsaturated acetals by treatment with Schlosser s base and subsequent trapping with triisopropylborate (entry 2) [228]. 

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