Organofluorverbindungen und Fluorierungsagenzien 12¹. Von manno-Pyranosiden zu 3,4-O-(2,2,2-Trichlorethyliden)altropyranosylfluoriden in nur zwei Reaktionsschritten

Organofluorine Compounds and Fluorinating Agents 12.¹ From manno-Pyranosides to 3,4-O-(2,2,2-Trichloroethylidene) altropyranosyl Fluorides in Only Two Reaction Steps Methyl α-D-mannopyranoside (1) and methyl α-L-rhamnopyrano-side (9) react with chloral and dicyclohexylcarbodiimide (DCC) in an one-pot reaction selectively to form the α-D-altropyranoside 2 and α-L-altropyranoside 10, respectively, in good yield. The glycosyl donor 3 was prepared from 2 by treatment with hydrogen fluoride/nitromethane/acetic anhydride. Compound 2 can be deprotected stepwise by treatment with methanol/sodium methanolate at r.t. to 4, and heating under reflux to methyl 3,4-O-(2,2,2-trichloroethylidene)-α-D-altropyranoside (5). Treatment of the dihydroxy derivative 5 with hydrogen fluoride/nitromethane/acetic anhydride gave an anomeric mixture of the α/β-D-altropyranosyl fluorides 6. Acylation of 5 with benzoyl or pivaloyl chloride gave the corresponding 2,6-diacyl derivatives 7 and 8, respectively. Finally, the α-L-altro-pyranoside 10 was deprotected in boiling methanol/sodium methanolate to afford the α-L-altropyranoside 11 and fluorinated in hydrogenfluoride/nitromethane/acetic anhydride to α-L-altropyranosyl fluoride 12. The various functionalized altropyranoses differ partially in their conformations. The ratio of the endo-H to exo-H diastereomers of the chloral acetals was determined.