Levent Yüceer

Tricyclic ortho ester formation from trichloroethylidene acetals of sugars via ketene acetals

Abstract One step formation of the tricyclic dichloroethylidyne ortho esters from the reaction of trichloroethylidene acetals of D-galactose and D-arabinose with K tert-butoxide are described. The possible intermediate, i.e, ketene acetal was prepared separately, from the suitably protected 1,2-O-trichloroethylidene-α-D-galactofuranose. Stereoselective formation of an ortho ester anhydride, from the ketene acetal is also described.

1,2-O-Trichloroethylidene acetal group protected 3,5-dieno-1,4-furanose derivatives

The preparation of 3,5-(E)-dieno-3,5,6,8-tetradeoxy-(S)-1,2-O-trichloroethylidene-alpha-D-glycero-octo-1,4-furano-7-ulose starting from either 1,2-O-(S)-trichloroethylidene-alpha-D-glucofuranose (beta-chloralose) or 1,2-O-(S)-trichloroethylidene-alpha-D-galactofuranose (galactochloralose) and the preparation of methyl 3,5-(E)-dieno-3,5,6-trideoxy-(S)-1,2-O-trichloroethylidene-alpha-D-glycero-hepta-1,4-furano-uronate starting from beta-chloralose are described. Endocyclic double bond formations were realised by the elimination of 3-acetoxy groups using DMF-sodium bicarbonate. This elimination was not successful when the starting compound was 1,2-O-(R)-trichloroethylidene-alpha-D-glucofuranose (alpha-chloralose), where the trichloromethyl group occupies the endo position.

Formation of the butylidene acetas of α-chloralose

Abstract The acid-catalysed reaction of α-chloralose 1 ( 1 , 1,2- O -trichloroethylidene-α- d -glucofuranose, the isomer having m.p. 190-195°) with butyraldehyde gave two stereoisomeric, crystalline 5,6- O -butylidene-1,2- O -trichloroethylidene-α- d -glucofuranoses ( 2 and 3 ). The structures of 2 and 3 were identified by chemical and spectroscopic means. The formation of the 3,5-acetal( 11 ) was not observed in the direct butylidenation of α-chloralose, but 11 could be synthesised by indirect routes. The butylidene acetal ring of 11 was hydrolysed much more readily than the butylidene group of 2 or 3 .

2-DICHLOROMETHYL-1,3-DIOXOLAN-2-YL ORTHOESTERS. A POTENTIAL PROTECTING GROUP FOR SUGAR DERIVATIVES

Reactions of 2-dichloromethylene-1,3-dioxolane (2) with acetal protected sugar derivatives in neutral media gave 2-dichloromethyl-1,3-dioxolan-2-yl orthoesters. These orthoesters are readily hydrolysed under mild acidic conditions offering a new method for the preparation of readily removable protecting groups. This strategy was realised in the preparation of 6-O-acetyl-3,5-di-O-methyl-1,2-O-isopropylidene-α-d-glucofuranose.

Synthesis of New Spirodifuranose Derivatives by Reduction of Stable Spiro-Endoperoxides

Synthesis of three new stable spirodifuranose derivatives (3, 5, and 7), which cannot be obtained easily using ordinary synthetic methods, has been achieved by reduction of 3-O-acetyl and 3-O-methyl derivatives of (4R)-1,2-O-alkylidene-5-eno-4,7-epidioxy-5,6,8-trideoxy-α-D-threo-1,4-furano-4,7-diulo-octoses (1, 4, and 6).