Synthesis of Novel Cyclobutane Nucleoside Analogues

A synthesis of cyclobutane nucleosides is described. The method involved the triflation of a -hydroxymethyl-cyclobutanone and its subsequent displacement by a 6-chloropurinyl anion to generate N-7 and N-9 regioisomers. The stereoselective reduction of the N-alkylated ketones yielded the cis-alcohols quantitatively and the geometric configuration was confirmed by spectroscopic data and X-ray diffraction. Photolysis of N-7 and N-9 coupled ketones was carried out in methanol using quartz tubes to promote ring-expansion isonucleoside products. Photolysis did not yield any ring-expansion or cycloelimination products, rather, the products are suspected to be cyclopropanes from decarbonylation of the ketones, since these are less polar and show shielding of protons in their corresponding NMR spectra, consistent with substituted cyclopropanes.