Triphenylbismuthonium ylides

Triphenylbismuthonium ylide reacted with terminal alkynes in the presence of a catalytic amount of copper(I) chloride to form furan derivatives (Scheme 11) [27]. Although the yields were low, the products were obtained regioselectively. The reaction was sensitive to steric factors, and internal alkynes did not provide the product. A carbenoid intermediate was probably involved in the reaction. 

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). 

The first bismuthonium ylide to be prepared and isolated was triphenylbismuthonium tetraphenylcyclopentadienylide, made by thermal decomposition of diazotetraphenylcyc-lopentadiene in the presence of triphenylbismuth . More recently some other bismuthonium ylides (Pli3Bi=CX2, X = RCO or RSO2) have been prepared and isolated by the diazo method, using copper hexafluoroacetylacetonate as catalyst... 

Triphenylbismuthonium tetraphenylcyclopentadienylide is stable for some time as a solid but decomposes rapidly in solution it decomposed rapidly when treated with acid or with base. Acyl and sulphonyl bismuthonium ylides are moderately stable, but less so than their arsonium and stibonium analogues some, while stable in solution in inert solvents, decompose when isolation is attempted ... 

A number of triphenylbismuthonium diacylylides and also the diphenylsulphonylylide undergo transylidation when treated with dimethyl sulphide in the presence of copper(I) chloride in benzene at room temperature, giving the corresponding dimethylsulphonium ylides no such reaction took place with diphenyl sulphide Some of these bismuthonium ylides reacted with triphenylarsine or triphenylphosphine and were converted thereby into arsonium or phosphonium ylides they did not react with triphenylstibine L The conversion of the diacetylylide into the 4,4-dimethyl-2,6-dioxocyclohexylide as mentioned in Section IX.A should also be noted. 

Reaction of 2-oxoalkyltriphenylbismuthonium salts (82) with a base such as potassium tert-butoxide led to triphenylbismuthonium 2-oxoalkylides (86). These compounds showed the behaviour of moderately stabilized ylides towards various nucleophiles. 5-67... 

When treated with a base such as THF at low temperatures, 2-oxoalkyl-triphenylbismuthonium salts are readily converted to bismuthonium 2-oxoalk-ylides, whereas 3-oxoalkyltriphenylbismuthonium salts undergo )8-elimination to afford a, )8-unsaturated ketones and triphenylbismuthine... 

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]. 

Triphenylbismuthonium 2-oxoalkylides readily couple with a-dicarbonyl compounds in several different reaction modes [96CC2697, 98CC1359J. When treated with ethyl pyruvate, the epoxidation proceeds to form 2,3-difunctionalized oxiranes. The reaction with benzils gives O-aroylenolates derived from 1,3-diketones, while treatment with o-quinones affords 2-acyl-1,3-tropolone derivatives. These reaction modes are unprecedented in the ylide chemistry. 

Scheme 5.34. Typical reactions of (2-oxoalkyl)triphenylbismuthonium salts and their derived ylides.

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