Pseudosugars, 37. Preparation of Versatile Intermediates for Ether‐Linked 5a‐Carba Oligosaccharides: Synthesis of 5a‐Carba‐β‐ D ‐Glc p NAc‐(1→4)‐ D ‐Man p

Coupling of 1,2‐anhydro‐3‐ O ‐benzyl‐4,6‐ O ‐benzylidene‐5a‐carba‐β‐ D ‐mannopyranose ( 3 ) with 1,6‐anhydro‐2,3‐ O ‐isopropylidene‐β‐ D ‐mannopyranose ( 4 ) afforded a 5a′‐carba disaccharide derivative linked by an ether bridge with α‐ manno configuration. This compound 5 was transformed into three stereoisomers in regard to the configurations at C‐1′ and C‐2′. Thus, the free 2′‐hydroxyl group was oxidized, and the resulting ketone 8 was isomerized at C‐1′ to 11 by treatment with potassium tert ‐butoxide. Reduction of the ketones 8 and 11 with l ‐selectride afforded selectively the synthetic useful intermediate ether‐linked 5a′‐carba disaccharides 9 , 12 , and 14 with α‐ gluco , β‐ gluco , and β‐ manno configurations, respectively. 5a‐Carba sugar analog 2 of biologically interesting disaccharide β‐ D ‐Glc p NAc‐(1→4)‐ D ‐Man p ( 1 ) was synthesized.