The Reaction of Dimeric Tri-O-acetyl-2-deoxy-2-nitroso-α-D-hexopyranosyl Chlorides with Alcohols

The kinetics of the reactions of dimeric tri-O-acetyl-2-deoxy-2-nitroso-α-D-glucopyranosyl chloride (1) with simple aliphatic alcohols (4 mol equiv) in dimethylformamide to form alkyl tri-O-acetyl-2-oximino-α-D-arabino-hexopyranosides (5) were investigated by n.m.r. and optical rotation. It is concluded that the conversion of 1 to 5 proceeds basically by way of three successively formed intermediates, namely, the monomeric form (2) of 1, the tri-O-acetyl-2-oximino-α-D-arabino-hexopyranosyl chloride (3), and the tri-O-acetyl-1,5-anhydro-2-deoxy-2-nitroso-D-arabino-hex-1-enitol (4). Direct evidence was obtained only for the intermediacy of 3 and the transient existence at low concentration of an uncharacterized intermediate which may be the β-anomer of 5. The intermediate 4 could form directly from 2 and thereby provide a mechanism for the formation of 5 which by-passes 3. However, the kinetic investigations showed this route to be of very minor, if any, importance. In all cases, the rate of the disappearan...