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Zahlreiche, z,T; sterisch gehinderte geminale Dicarbonsäureester (I) werden mit den Basen (IV)‐(VI), z.B. in Toluol, zu den Monoestern (II) und den entsprechenden Monocarbonsäuren (III) umgesetzt.

2917 (1971). (12) 'H and ' ' F nmr spectra were obtained on Jeol PS 100 spectrometer. Mass spectra were recorded on a CEC 21-llOC spectrometer. Melting Doints were determined on a Kofler melting point apparatus and are un-I k p a r t m e n t of C h r m i s t n , Mississippi State L'niuersity, Mississippi State, Mississippi 39762 H e w i w d March 8, 1974As a result of a continuing study utilizing nitrogenous bases,' . I we now wish to report that 1,4-diazabicyclo[2.2.i2]octane (Dabco) is useful for the cleavage of @-keto esters.Aj-Keto ester 1 was treated with 6 equiv of Dabco in 16 equiv of o-xylene a t reflux (165') for 6 hr to give ketone 10 as a white, crystalline solid in 84% yield. Ketone 10 was identical by ir, nmr, mass spectrum, glc retention time, and mixture melting point with an authentic sample prepared from 1 by a known procedure.5The generality of Dabco as a reagent for cleaving B-keto esters is demonstrated by the results illustrated in Scheme I. Typically, a mixture of 1 equiv of the appropriate b-keto ester and 10 equiv of I>abco in 15 equiv of o-xylene was heated to reflux for 4 hr." The resulting ketones (11-14) were obtained in greater than 96% yield by glc analyses and were identical by mass spectral and glc retention time comparison with authentic samples.",xThe selectivity of the cleavage reaction is demonstrated by the application of Dabco to the cleavage of substrate 9 to give compound 15. This result shows that only the 0keto esters with a t least one (Y hydrogen were cleaved. The report" that a variety of nonconjugated esters are stable under conditions similar to those which cleaved $-keto esters provides further evidence of selectivity.'I'he facile cleavage of methyl, ethyl, and n-butyl @-keto esters with a reagent (Dabco) that does not cleave saturated esters by either the 0-alkyl cleavage or hydrolytic routes suggests that a mechanism similar to that reported by Krapcho and I,ovey5,12 for the cleavage of &keto esters with sodium chloride and DMSO is probably operative.

Reduction of 4(5)-nitroimidazole-5(4)-sulfonamide afforded the sulfonamide analogue of 4(5)-aminoimidazole-5(4)-carboxamide (AICA). This was formylated to afford the sulfonamide analogue of formyl-AICA and was ring closed to the unsubstituted 6-sulfonyl analogue of guanine, 3-aminoimidazo[4,5-e]-1,2,4-thiadizine 1,1-dioxide. Diazotiz ation of the latter afforded the corresponding 6-sulfonyl analogue of xanthine. None of the imidazole-sulfonamides or the purine 6-sulfonyl analogues inhibited the growth of L1210 cells in culture nor were they substrates for or significant inhibitors of human hypoxanthine--guanine phosphoribosyltransferase or milk xanthine oxidase.

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