Abstract
The synthesis and structural characterisation of phosphine-substituted alkynylboronates is reported. A P(III)-centred alkynylboronate (2) was prepared that showed little evidence for the conjugation of the P-lone pair to the boron via the alkyne π-system, as judged by X-ray crystallography studies of 2 and a related P(V) compound, 3. In addition, corresponding alkynyltrifluoroborate salts were prepared that showed improved stability by comparison to their boronic ester counterparts. These salts undergo Pd-catalysed cross-coupling reactions with aryl halides.
Highlights
Since their discovery by Matteson in 1960 [1], alkynylboronates have proven to be a versatile and popular class of synthetic intermediates in organic synthesis
An early example of an ynol ether-derived alkynylboronate [21] suggested that these compounds were unstable, and this precluded extensive studies into their synthetic chemistry and their structural characterisation
Evidence for related mesomeric B-C π-bonding in alkynylboronates has been documented by Yamamoto [22], and it seemed feasible that this would be enhanced by the inclusion of an appropriate Lewis basic donor
Summary
Since their discovery by Matteson in 1960 [1], alkynylboronates have proven to be a versatile and popular class of synthetic intermediates in organic synthesis. They combine the traditional nucleophilic properties of alkyne-based organometallics and, as such, undergo metal catalysed cross-coupling [2,3,4], as well as addition to aldehydes and imines [5]. These reagents are Molecules 2014, 19 subject to chemistry at the triple bond. We report our studies on the synthesis, characterisation and reactions of phosphine-substituted alkynylboronates and their closely-related trifluoroborate salts
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