[21860-46-8] · C10H10O3S · 4-Phenylsulfonyl-3-buten-2-one · (MW 210.27)
(methyl vinyl ketone equivalent which does not undergo polymerization; dienophile)
Physical Data: needles, mp 61-62 °C.
Solubility: insol water; sparingly sol pentane, hexane; sol most other organic solvents.
Preparative Methods: from Methyl Vinyl Ketone and Thiophenol in chloroform followed by treatment with N-Chlorosuccinimide and base-catalyzed dehydrochlorination to give the 4-phenylthiobut-3-en-2-one,2 oxidation of which with m-Chloroperbenzoic Acid in ether gives a mixture of geometric isomers of the sulfone.3 Sodium Benzenesulfinate and (E)-4-Chloro-3-buten-2-one in methanol give the (E) isomer only.4 Other preparations are from acetylaldehyde dimethyl acetal5 and phenylsulfonylmethyl p-tolyl sulfoxide and propionaldehyde.6
Handling, Storage, and Precautions: no special precautions are required although storage at 4 °C or lower will prolong its shelf-life. It is also recommended to protect from light as isomerization to the (Z) isomer takes place.
Like 4-chlorobut-3-en-2-one, the sulfone serves as an effective methyl vinyl ketone equivalent in the conjugate addition of lithiated carbanions under aprotic conditions.4,7 In an addition-elimination sequence the sulfonyl group is less reactive than the chlorine and sometimes leads to addition only to give sulfone products.8 When elimination is desired under very mild conditions, then the related 4-sulfinylbut-3-en-2-one is a preferred reagent.8 For example, the latter reagent undergoes conjugate addition with heteronucleophiles such as Furan and pyrroles in the presence of p-Toluenesulfonic Acid to form ketovinyl derivatives8 and a double conjugate addition with diimines under neutral conditions to afford 2-acetonyl-1,2-dihydropyrimidines (eq 1).5
With two electron-withdrawing substituents the sulfone has an electron-deficient double bond and as such is a good dienophile. Under solvent-free conditions it reacts rapidly and cleanly with relatively inactive dienes. For example, when 4-phenylsulfonylbutenone and cyclohexadiene are adsorbed on silica, adduct formation proceeds in nearly quantitative yield after 35 h at room temperature.9 However, stereoselectivity is poor, giving an endo:exo ratio of 5:6. When more reactive dienes are employed such as furan and 1-methoxycyclohexa-1,3-diene, selectivity for the endo adduct increases to 8:1 and 12:1, respectively. Elimination of the sulfonyl group by the use of Sodium Ethoxide is facile, affording the corresponding alkenes in very high yields. Thus the sulfone functions as an a,b-alkynic ketone equivalent (eq 2).
Richard K. Haynes
Hong Kong University of Science and Technology, Hong Kong
Simone C. Vonwiller
The University of Sydney, NSW, Australia