Effect of base on alkyltriphenylphosphonium salts in polar aprotic solvents
When arylmethyl phosphonium salts are treated with a base (e.g., t-BuOK or NaH) they homocouple to form symmetric 1,2-diarylethenes. In some cases, dilution and (or) use of excess base lead to very high yields of the product. This reaction is solvent sensitive: the reaction occurs only when polar ap...
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Veröffentlicht in: | Canadian journal of chemistry 2008-07, Vol.86 (7), p.668-675 |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | When arylmethyl phosphonium salts are treated with a base (e.g., t-BuOK or NaH) they homocouple to form symmetric 1,2-diarylethenes. In some cases, dilution and (or) use of excess base lead to very high yields of the product. This reaction is solvent sensitive: the reaction occurs only when polar aprotic solvents such as acetonitrile or DMSO are used. Other alkyl phosphonium salts (e.g., ethoxycarbonylmethyltriphenylphosphonium bromide and n-butyltriphenylphosphonium bromide) form a ylid (when an α-carbonyl group is present) or lose a phenyl group to form alkyldiphenylphosphine oxides when treated with the base. Mechanistic investigation of the homocoupling reaction indicates that the reaction proceeds through a ylid that acts as a nucleophile on an unreacted phosphonium salt. The resulting adduct undergoes elimination to form the observed product. The E/Z ratio seems to depend on the amount of the base used and the phosphonium salt involved.Key words: phosphonium salts, homocoupling, 1,2-diarylalkene, Ylids. |
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ISSN: | 0008-4042 1480-3291 |
DOI: | 10.1139/v08-056 |