Organoboron monosaccharides, XVI. Selective syntheses of the methyl α‐ D ‐furanosides of Lyxose and Mannose using ethyl(dimethoxy)borane

Ethyl(dimethoxy)borane is prepared by a two‐step method involving reaction of triethylboroxin with 1,4‐butanediol in a molar ratio of 1:3 to give oligomeric 1,4‐butanediyldioxy‐ethylboranes which are then treated with methanol. D ‐Lyxose ( 1 ) reacts selectively with ethyl(dimethoxy)borane in the presence of acidic ion exchange resin to form methyl 2,3‐ O ‐ethylboranediyl‐α‐ D ‐lyxofuranoside ( 2 ) which is deboronated to give methyl α‐ D ‐lyxofuranoside ( 4 ). Similarly, D ‐mannose ( 6 ) reacts to give methyl 2,3:5,6‐bis‐ O ‐ethylboranediyl‐α‐ D ‐mannofuranoside ( 7 ), the deprotection of which yields methyl α‐ D ‐mannofuranoside ( 8 ).