Bismuthonium stabilized

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 stability of these bismuthonium salts (82) - (85) depends on the nature of the anionic counterpart and of the fourth ligand. The allyl derivatives (84) are too unstable to be isolated. On the other hand, the tetrafluoroborate salts of the derivatives of the three other types of onium compounds are thermally stable. Ligand coupling- type products are formed with more nucleophilic anions, for example during the attempted exchange of anion with bromide or iodide, or during the slow decomposition of a solution of bismuthonium tosylates in chloroform. ... 

Moreover, the synthesis and good stability of the covalent carbon-bismuth compound in the case of acetone, 2-oxopropyltriphenylbismuthonium perchlorate, excluded this type of intermediate as a common pathway, although this view was questioned by Suzuki et The reaction of the sodium salt of acetylacetone with triphenylbismuth dichloride led to a bismuthonium salt (37) decomposing slowly at room temperature to give eventually 3-phenylpentane-2,4-dione (35). ... 

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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