Tricyclic furanoid dichloroacetyl orthoesters of d-mannose from 1,2-O-trichloroethylidene-β-d-mannofuranose Original Research Article

1,2-O-(R)-Trichloroethylidene-β-d-mannofuranose (1) was obtained from the reaction of d-mannose with chloral. Reaction of 1 with potassium tert-butoxide (3 M equiv) gave the thermodynamically stable 1,2,5-O-orthodichloroacetyl-β-d-mannofuranose as the sole product whereas 1.5 M equiv of reagent gave the kinetically controlled 1,2,3-O-orthodichloroacetyl-β-d-mannofuranose (10) as the main product. Orthoester 10 gave the 5,6-isopropylidene derivative, which was also obtained from the reaction of 5,6-O-isopropylidene-1,2-O-(R)-trichloroethylidene-β-d-mannofuranose with potassium tert-butoxide (1.5 M equiv). These novel orthoesters are expected to prove useful as protecting groups and as building blocks in the formations of new mannofuranisidic units.