Norbornadiene, dimethyl acetylenedicarboxylate. and vinyl ethers react with the sulphenic acids produced by heating penicillin S-oxides. Norbornadiene, diketen (4-methyleneoxetan-Z-one), and dimethyl acetylenedicarboxylate react by addition, whereas vinyl ethers, such as dihydropyran, react by substitution with loss of water. Methanolysis of the vinyl ether products can be achieved with dilute methanolic hydrochloric acid. Removal of the nitrogen-containing substituent of the @-lactam ring from the vinyl ether products has been effected via the pyrazoline route. A novel substitution reaction occurs on heating the 3-hydroxypenam ( 22) with acrylaldehyde : methacrylaldehyde is displaced and the 4-hydroxycepham (25) is formed. Some reactions of this cepham are reported.SULPHENIC ACIDS are known to undergo electrocyclic addition t o olefinic double bonds2 For example, 1 ,l-dimethylethanesulphenic acid, prepared by the thermolysis of di-t-butyl sulphoxide at SO", readily adds t o electrophilic olefins at room temperature.
The isomeric sulphoxides of 6~-phenylacetamidopenicillanic acid esters and N-t-butyl-amides have been prepared. The ( R ) -sulphoxides can be thermally converted into the (S) -isomers. Deuterium labelling showed that the isomerisation proceeds via a sulphenic acid intermediate. Rearrangement of the sulphoxides with acetic anhydride produces mainly the corresponding acetoxypenams and acetoxycephams. Both isomers of the acetoxy-substituted penam can be formed by isomerisation of the appropriate sulphoxide.
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