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Abstract-Thiol addition to acetylcnic sulfones in the 1 -methylsulfonyl -2 -arylethyne series has been investigated. In analogy with earlier reports on thiol additions to arylsulfonyl -I -alkynes no violations of the Irons-addition rule have been observed. Besides the expected nucleophilic attack on the PC-atom, considerable a-addition occurred.In the course of a research programme on the design of new This may be envisaged by the correspondence between agricultural fungicides it was found that I-alkylsulfonyl-tthe chemical shifts of the olefinic protons in the NMR arylethynes, 1, possess interesting fungicidal properties.' The presumed mode of action of these compounds,' viz. an spectrum for compounds 3a-d (Table 2) as compared with 5 for which the olefinic proton resonance is reported' to irreversible reaction of thiols occurring within fungal cells, appear at 6.35 ppm.X C=C-SO,R 1 prompted us to investigate the nucleophilic addition of some model thiols. Thiol additions to acetylenic sulfones have been described earlier for alkylsulfonyl-and arylsulfonyl -1 -alkynes.>' In contrast with the addition of amines-to acetylenic sulfones, thiol addition was found to proceed in a stereospecific way, i.e. the frans-addition rule was followed in all instances.In our study a set of acetylenic sulfones 2 was selected with substituents X so as to cover a wide range of Hammett u-values.The additions were carried out at room temperature in a 1: I mixture of EtOH and DMF to ascertain a kinetic control of the reaction. The thiols used were methane thiol and n-butanethiol, which were added to the substrates in equimolecular quantities either as such under the catalytic influence of a piece of sodium or as their sodium salts. It was expected that only the Z-isomer, resulting from a nucleophilic attack on the PC-atom, would be obtained. However, the base-catalysed reaction of 2a-c with methanethiol afforded a mixture of essentially three components. Only traces of ethoxide adducts formed by reaction with the solvent could be detected.The components were separated by column chromate graphy. The compound with the lowest R, value was assigned the configuration of the "normal" thiol adduct 3.
Regression analysis in the l‐alkylsulphonyl‐2‐arylacetylene series yielded significant correlations of antifungal activity against six microorganisms with certain physicochemical parameters (electronic effects, lipophilicity and steric factors). Fungicidal activity is enhanced by introducing electron‐withdrawing substituents in the aryl nucleus, whereas variation of the lipophilic parameter reveals an optimum value. The results obtained indicate a mechanism of action based on a reaction of the compounds with nucleophiles present in the fungal cells, which was confirmed by determining the second‐order rate constants of the reaction between 1 ‐alkylsulphonyl‐2‐arylacetylenes and the model nucleophile 4‐nitro(thiophenol). The lipophilic para‐meter was also determined experimentally using thin‐layer chromatography. Regression analysis with this completely experimental set of parameters regression gave highly significant results in close agreement with those obtained above.
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