Synthesis and Reactions of C-Hetaryl Substituted Ketoses

O-Benzyl protected gluconolactone 1 reacts readily with 2-lithio derivatives of quinaldine, 2-methylquinoxaline, 2-methylbenzimidazole and N-protected derivatives, and 1-benzyloxymethyl-2-methylimidazole at low temperatures to afford as monoaddition products the corresponding D-gluco-2-heptuloses 2-5. The benzyl protective groups can be readily removed by hydrogenolysis as shown for the transformation of 4a into 8. Acylation reactions with 4a exhibited an interesting interplay between O- and N-acylation which is dependent on the nature of the acylating agent and on the reaction conditions. Reductive removal of the anomeric hydroxy group in 4a-c and 5 was readily performed via elimination products 18a-c and 23; their hydrogenation with Pd/C gave directly the O,N-deprotected C-ß-D-glucopyranosylmethyl derivatives 21 and 25, respectively.