Enolate ions sulfenylation

N-Allenylazetidinone 181 rearranges to cephalosporin 182 in the presence of lithium chloride (Eq. 13.62) [70], This is a very unusual reaction that is presumed to be initiated by chloride ion-induced cleavage of the disulfide to give sulfenyl chloride 183. Thiolate attack at the allene sp carbon atom of 183 generates ester enolate 184, which cyclizes to 182. The reactivity of the allene function in 181 ensures the success of the reaction. 

As the accompanying equations illustrate, the reactions of enol silyl ethers are regarded as those of either electron-rich olefins or stable metal enolates. The treatments of eno/ silyl ethers with halogens, NBS, sulfenyl halides, and nitronium ions afford the corresponding a-halo, alkylthio, and nitro ketones, respectively (eq (22)) [19]. 

Further reaction of the sulfenyl chlorides to the sulfides does not take place. It can also be deduced that the substitution reaction occurred with the chelate ring unruptured, since no sulfides (usually obtained with sulfur dichloride and the enol form of 2,4-pentanedione) were obtained. The structures of the sulfenyl chlorides of the metal acetylacetonates were confirmed by their infrared spectra, and by conversion of the sulfenyl chloride to a thiocyano group by reaction with cyanide ions. The tris(3-thiocyano-... 

Alkylation of j8-diketones using polymers as supports for the intermediate enolate anion has also been reported (Gelbard and Colonna, 1977). Reaction of several cyclohexyl j3-diketones with Amberlite IRA-9(K) formed a resin-linked j8-diketonate that could be readily alkylated. Similarly, it was shown that alkylation of phenoxide anions can be readily effected when the anions are supported via an ionic bond with the resin (Gelbard and Colonna, 1977). Alkylations of /3-diketones were also shown to occur if a fluoride-substituted, strongly basic resin (Amberlyst A26, A27, or Dowex MSA-1) is used (Miller et at., 1978). In this case, the presence of the fluoride ion was necessary before reaction would proceed. Considering the report on the use of Amberlite IRA-900— a very similar resin— the necessity for a fluoride ion is puzzling. In the same publication, the 0-alkylation of phenols, the sulfenylation of /3-diketones, and the Michael addition of a thiol to an ot,/8-unsaturated ketone were also investigated. 

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