112182-61-3Relevant articles and documents
Detection and kinetic characterization of SNV intermediates. Reactions of thiomethoxybenzylidene Meldrum's acid with thiolate ions, alkoxide ions, OH-, and water in aqueous DMSO
Bernasconi, Claude F.,Ketner, Rodney J.,Chen, Xin,Rappoport, Zvi
, p. 584 - 594 (1999)
The reaction of thiomethoxybenzylidene Meldrum's acid (5-SMe) with thiolate and alkoxide ion nucleophiles is shown to proceed by the two-step addition-elimination SNV mechanism in which the tetrahedral intermediate accumulates to detectable levels. For the reactions with thiolate ions, rate constants for nucleophilic addition (k1RX), its reverse (k-1RX), and for conversion of the intermediate to products (k2RX) were determined. For the reactions with alkoxide ions, only k1RX and k-1RX could be obtained; the intermediate in these reactions did not yield the expected substitution products, and hence no k2RX values could be determined. The reaction with OH- and water are believed to follow the same mechanism, but the respective intermediates remain at steady-state levels, and only k1OH and k1H2O for nucleophilic attack on 5-SMe were measurable. New insights regarding structure-reactivity behavior in SNV reactions are gained from comparisons of rate and equilibrium constants in the reactions of 5-SMe with the corresponding parameters in the reactions of methoxybenzylidene Meldrum's acid (5-OMe) and benzylidene Meldrum's acid (5-H). In particular, the relative importance of steric and π-donor effects of the MeS vs. MeO group in 5-SMe and 5-OMe, respectively, and their role in affecting the intrinsic rate constants for nucleophilic addition, has been clarified by these comparisons. Our results also add support to a previous suggestion that soft-soft type interactions tend to increase intrinsic rate constants for thiolate ion addition to vinylic substrates, especially 5-SMe with the soft MeS group.
Synthesis of 3-hydroxythiophenes and thiophen-3(2H)-ones by pyrolysis of alkylsulfanylmethylene Meldrum's acid derivatives
Hunter, Gordon A.,McNab, Hamish
, p. 1209 - 1214 (2007/10/02)
3-Hydroxythiophene 1 and a range of its 2-substituted, 2,2-disubstituted and 5-substituted derivatives have been made by flash vacuum pyrolysis (FVP) of an appropriate alkylsulfanylmethylene derivative of Meldrum's acid 3 or 4.These compounds are readily obtained, either by reaction of methoxymethylene Meldrum's acid with alkylthiols in refluxing acetonitrile, or via the bis(methylsulfanyl) compound 18 by known procedures.The pyrolysis proceeds by a hydrogen-transfer-cyclisation mechanism in which thereis extensive loss of configuration of a chiral centre at the reaction site.The NMR and mass spectra of the Meldrum's acid precursors and the mass spectra of the 3-hydroxythiophenes are briefly discussed.
