It was established in the study of catalytic reactions between diazo carbonyl compounds and oxoisothiazole 1,1-dioxides and their acyclic analogs that the reaction resulted exclusively in the O-alkylation of the carbonyl group in the sulfonimide fragment of the molecule (SO 2 NHCO) with formation of O-alkyl imidates which formally were products of a carbene insertion into the OH bond of the enol form of imides under consideration [1]. The conversion of sulfonamides I into O-alkyl imidates II involved apparently the primary attack on the oxygen of C=O group of electrophilic ketocarbenoid A giving an intermediate carbonyl ylide B [2], which was further stabilized into O-alkyl derivatives of imide II as a result of an intramolecular [1,4]-sigmatropic shift of the proton from the NH group to the anionic center of intermediate B [3]. In order to identify the presumed intermediate carbonyl ylide B in the course of reaction by chemical methods we carried out a series of experiments using dimethyl acetylenedicarboxylate as the most efficient trap for reactive 1,3-dipoles [2]. It was established that in the course of catalytic decomposition of diethyl diazomalonate in the presence of saccharin (Ia) containing a free NH bond and of dimethyl acetylenedicarboxylate (III) formed the same O-alkyl imidate IIa as in the absence of dipolarophile, and not a cycloadduct of compound III to carbonyl ylide B.This fact apparently testifies to the faster occurrence of the stabilization of the intermediate carbonyl ylide B via intramolecular 1,4-migration of a proton than its intermolecular reaction with dimethyl acetylenedicarboxylate. Therefore we expected to obtain cycloadducts of carbonyl ylide B with dipolarophile III at the use under the same conditions of N-substituted sulfonamides lacking a hydrogen on the imide group able to migrate.It proved however that the analogous catalytic reaction of dimethyl diazomalonate and diazoacetylacetone with N-methyl and N-phenylsubstituted isothiazole 1,1-dioxides (Ib and Ic) in the presence of reagent III also did not afford the cycloadducts with the dipolarophile. In both cases after the workup of the reaction mixture we recovered initial N-methyl and N-phenylsaccharins (Ib and Ic), and according to 1 H NMR spectra was also revealed the formation of a dimer bis(methoxycarbonyl)carbene.To clear the reason of the failure to achive the carbonyl ylide addition to dipolarophile III in the course of intermolecular generation of ylides from N-substituted 6 1 2 5 ; / 5K B a+ 5 + , ,F B / 5K &5 5 $ 6 1 2 5 ; B 5 5 6 1 2 ; ,, 2 &5 5 + 2 2% X = (CH) 4 , R 1 = H, R 2 ,R 3 = CO 2 Et (a); X = (CH) 4 , R 1 = Me, R 2 ,R 3 = CO 2 Me (b); X = (CH 2 ) 4 , R 1 = Ph, R 2 ,R 3 = COMe (c).
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