Bismuthonium ylides stability

Stabilized bismuthonium ylides have also been made from compounds having reactive methylene groups, CH2CXY, X, Y = RCO or RSO2, either by making their sodium salts and letting the latter react with dichlorotriphenylbismuth, or by reaction with triphenyl-bismuth oxide 1 181. 

The 1,3-oxathiole 3,3-dioxides (331) are formed by treatment of a silyl enol ether (330) with an a-halosulfonyl bromide followed by dbn (Equation (56)) <84JOC3664> and the similar compounds (333) can be prepared by reaction of the stabilized bismuthonium ylides (332) with a sulfene (Equation (57)) <89cci749>. 

The reaction of triphenylbismuth carbonate with cyclic 1,3-dicarbonyl compounds, such as dimedone and Meldrum s acid, gives highly stabilized triphenylbismuthonium ylides (Section 3.5.1). Moderately stabilized acyclic bismuthonium ylides can be prepared from triphenylbismuth dichloride and a 1,3-diketone or a 1,3-disulfone in the presence of a suitable base. A similar base-promoted reaction of triphenylbismuth dihalides with Al-sulfonylamines or amides has been used for the preparation of stabilized bismuthine imides bearing the Af-sulfonyl or Af-acyl moiety (Section 3.6.1). 

A stable bismuthonium ylide is formed by the reaction between triphenyl-bismuth carbonate and dimedone [85JCS(P1)2667]. The cyclic a,a -dioxo structure is likely to be the main origin of high stability. 

Stabilized bismuthonium ylides bearing a cyclic or acyclic a,a -dicarbonyl or a,a -disulfonyl skeleton can be prepared from triphenylbismuth dihalides and the corresponding 1,3-diketones or 1,3-disulfones in the presence of a suitable base [88CL847, 89CC1749, 94JFC(66)75J. 

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. 

Copper(I)-catalyzed reaction of a stabilized bismuthonium ylide with phenylacetylene... 

All the characteristic reactions of stabilized and moderately stabilized bismuthonium ylides are described in Section 5.4.3.3 with reaction schemes. 

Scheme 5.33. Typical reactions of a stabilized bismuthonium ylide derived from dimedone.

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