New direction in sulfenylation of dimethyl endo,endo-bicyclo[2.2.2]oct-5-ene-2,3-dicarboxylate

Abstract

It is known1 that the reaction of dimethyl endo,endo bicyclo[2.2.2]oct 5 ene 2,3 dicarboxylate (1) with arene sulfenyl chlorides leads exclusively to the products of trans annullar cyclization involving the oxygen atom of the methoxy group, viz., γ and δ lactones, the ratio of which varies widely depending on the electronic characteristics of substituents in the arene ring of the sulfur containing electrophile. We found that the reactions of compound 1 with 3 methoxycarbonylpyridine 2 and 1,3 benzothiazole 2 sulfenyl chlorides (2 and 3), containing potentially nu cleophilic nitrogen atom in the hetaryl fragment, in ni tromethane in the presence of lithium perchlorate proceed by the mechanism of polar cycloaddition of the sulfenylat ing agent to the multiple bond.2—7 In these electrophilic processes, the nitrogen atoms of the hetaryl fragment of the starting agent are involved into the ring closure to form the polycyclic systems 4 and 5 in 87 and 84% yields, re spectively (Scheme 1). The structures of compounds obtained were con firmed by 1H and 13C NMR spectroscopy and elemen tal analysis data. The assignment of signals in the NMR spectra was made using COSY, HSQC, HMBC, and NOESY experiments. In the NOESY spectra of com pounds 4 and 5, the correlation peaks for the protons of the methoxy groups of the bicyclooctane framework with the protons H(2), H(10) and H(2), H(13), respec tively, are observed. At the same time, in the NOESY spectra the correlation peaks for the following pairs of protons are absent: H(2), H(14) and H(10), H(15) (in the spectrum of compound 4); H(2), H(17) and H(13), H(18) (in the spectrum of compound 5). These data indi cate the exo cis cycloaddition of the sulfenylating agent to the double bond.