Ohno s lactone

The rather low reactivity of the 3-p-tolylsulfinyl acrylates (they do not react with furan even under forcing conditions) prompted the search for more reactive dienophiles. In this context, pyridylsulfinyl derivatives proved to be more efficient than the arylsulfinyl ones. Thus, menthyl-3-(2-pyridylsulfinyl)propenoates 14a and 14b were prepared from (+)-menthyl propiolate in low yields [34]. Their reactions with cyclopentadiene proceed smoothly in the presence of Et2AlCl at -70°C to afford just one endo diastereoisomer 15a or 15b [35] (in the absence of the catalyst the 7r-facial selectivity for the endo approach was lower than that observed for the p-tolylsulfmyl derivatives [10c]). These compounds were transformed into 16a or 16b [36] respectively (Scheme 8), both allowing the synthesis of the bicyclic lactone 17 (known as Ohno s lactone), a key intermediate in Ohno s synthesis of (-)-aristeromycin and (-)-neplanocin A [37]. 

A short synthesis of the carbocyclic analogue of S-phosphoribosyl-1-pyrophosphate from the known (C.R. Johnson et al.. Tetrahedron, 1984, 40, 1225) chiral ketone 72 has been described. Syntheses of carba-a-D-arabinofuranose and of the carba-nucleosides (+)-cyclaradine and (+)- caH>a>P-D-arabinofuranosyluraciI from key intermediate nitro-compound 73 have been reported. A short synthesis of Ohno s lactone, 74 in 54% overall yield from (+)-(lR)-e/u/o-5-norbomene-2-carboxylic acid, as a useful carbocyclic nucleoside precursor, has been reported." See Chapter 20 for the synthesis of carbocyclic tiazofurin and other carbocyclic nucleosides. 

Further work on griseolic acid analogues has been reported (see Vol. 25, p. 232), giving guanosine analogues, e.g. 28, instead of adenine derivatives and its 3, 4 -stereoisomers together with carbocyclic analogues. Other carbocyclic nucleoside derivatives of aristeromycin and a synthesis of carbovir are mentioned in Chapter 20, and a synthesis of the carbocyclic nucleoside precursor, Ohno s lactone, is referred to in Cluster 18. 

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