Sequential cyclization-elimination route to carbohydrate-based oxepines.
A five-step preparation of carbohydrate-based oxepines from hept-1-enitols is presented. The hept-1-enitols were subjected to silyl protection and hydroboration/oxidation to give the protected heptan-1-itols. Swern oxidation of the homologated alcohols followed by sequential acetal formation/cyclization provided methyl 2-deoxyseptanosides that underwent elimination reactions to give the carbohydrate-based oxepines. The new sequence is an alternative to the ring-closing metathesis for the synthesis of carbohydrate-based oxepines from protected pyranose sugars. The product oxepines can serve as glycosyl donors in the synthesis of novel septanose carbohydrates. In addition, C-methylenealdehydo arabinofuranoside 16 was formed from 2-deoxyseptanoside 10 as the only product during protic acid mediated elimination reactions. This novel ring contraction complements other reported preparations of C-methylenaldehydo furanosides and underscores the acid-mediated reactivity introduced by competing eliminations between the C-1/C-2 and C-2/C-3 bonds.
Castro
Steve
S
Department of Chemistry, The University of Connecticut, 55 North Eagleville Road, U-3060, Storrs, CT 06269, USA.
Peczuh
Mark W
MW
D002241:Carbohydrates / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010082:Oxepins / Q000138:chemical synthesis*; D010084:Oxidation-Reduction
D002241:Carbohydrates; D007202:Indicators and Reagents; D010082:Oxepins