From bismuthonium salts and base

Abstraction of a-proton from 2-oxoalkyltriphenylbismuthonium salts by a base at low temperatures gives triphenylbismuthonium 2-oxoalkylides. The ylides cannot be isolated under ambient conditions due to thermal instability and moisture sensitivity. 

When a suspension of (3,3-dimethyl-2-oxobutyl)triphenylbismuthonium tetrafluoro-borate (126 mg, 0.2 mmol) in THF (5 ml) was mixed with potassium tert-butoxide (24 mg, 0.2 mmol) at — 78°C under argon, (3,3-dimethyl-2-oxobutylidene)triphenyl-A -bismuthane was formed as a yellow solution. Attempts to isolate this ylide under ambient conditions were unsuccessful due to its thermal instability and moisture sensitivity [94JCS(P1)2703]. 

Compound Synthetic method Yield (%) M.p. (°C) Physical data Reference 

The first bismuthonium ylide reported by Lloyd is a thermally stable colored substance, but the literature lacks details of its characterization. Several bismuthonium ylides containing a cyclic a,a -dicarbonyl or a,a -disulfonyl framework have been isolated as stable crystalline solids, and 4,4-dimethyl-2,6-dioxo-l-triphenylbismuthoniocyclohexane has been characterized structurally by X-ray crystallographic analysis, where the bismuth atom possesses a distorted tetrahedral geometry and interacts with one of the carbonyl oxygen atoms [90JCS(P1)3367]. The Bi-Cyude bond (2.156 A) is a bit shorter than the Bi-Cph bond (2.21-2.22 A), suggesting little or no double bond nature of the bismuth and ylidic carbon bond (Fig. 3.5). The ylidic carbon of this class of stabilized ylide appears at 8 100-113. 

Ph3Bi=CHC02R undergoes reductive dimerization at room temperature to give a good yield of triphenylbismuthine and a moderate yield of ethene R02CCH=CHC02R. 

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