A new preparation method for a variety of stable sulfur ylides is described. Reactions of the Corey-Kim reagent with active methylene compounds having two electron withdrawing groups in the presence of triethylamine afforded stable surfur ylides in satisfactory yields.
Highly stabilized sulfonium diacethylides (1a-c) reacted with acetyl chloride to give a mixture of the enol acetates (2a-c) and the enol diacetates (3a-c). Similarly, sulfonium acetylcarbomethoxymethylides (5a, b) gave the enol acetates (6a, b). These enol acetates were hydropyzed with HCl-MeOH to give 3-methylthio- (3-phenylthio-)2, 4-pentanediones (4a, b) or methyl 2-methylthio- (2-phenylthio-)acetoacetates (7a, b).
p-toluenesulfonamide gave N-p-toluenesulfonyl-S,S-dimethylsulfilimine 2. The reaction of 1 with carbon acids 3 having active methylene gave stable S-C ylids (exchange of S-N ylid for S-C ylid), while 2 reacted with malonitrile to give S-C ylid only in low yield. Thus, the ylid exchange mechanism based on the equilibrium including the protonated sulfonium salts has been assumed.
A novel route to sulphonium ylides, which consists in condensation of sulphoxides with active methylene compounds, gives stable, crystalline products I–XIII listed in Tables 1 and 2. NMR spectra of these ylides (Figs. 1–4) show remarkable temperature-dependence, the implications of which with respect to conformational equilibria have been discussed. Steric and electronic effects of aromatic Me groups
Disilyloxydienes (2a-c) were easily obtained by treatment of stable sulfur yliders (1a-c) with chlorotrimethylsilane in the presence of triethylamine. Cycloaddition reaction of these dienes with some dienophiles was carried out.