Preparation of acylated pyranoid glycals in neutral aqueous medium by using chromium(II) complexes as reagents

Article abstract of DOI:10.1016/S0040-4020(99)00170-2

Reactions of 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide (3) with chromium(II)L complexes (L = EDTA, NTA, IDA, GLY, MAL) in neutral (5 < pH < 7) aqueous DMF gave 3,4,6-tri-O-acetyl-1,5-anhydro-2-deoxy-D-arabino-hex-1- enitol (13) in 70-90% yields and > 95% purity. Complexes of Cr(II) with L = EDTA, NTA were similarly efficient with 2,3,4,6-tetra-O-acetyl-α-D- glucopyranosyl chloride (2) in furnishing glucal 13, while with L = IDA, GLY, MAL hydrolysis of 2 could not be suppressed. Under the same conditions [Cr(II)(EDTA)]^2- also efficiently gave the corresponding glycals 14-19 from 2,3,4,6-tetra-O-benzoyl- (4) and 2,3,4,6-tetra-O-pivaloyl-α-D-glucopyranosyl bromide (5), per-O-acetylated α-D-galactopyranosyl chloride (6) and bromide (7), α-D-mannopyranosyl chloride (8), α-D-xylopyranosyl chloride (9), and bromide (10), β-D-arabinopyranosyl bromide (11), and α-L-rhamnopyranosyl chloride (12).