Branched-chain Sugars. XXI. Synthesis of New Branched-chain Cyclitols Having neo-, myo-, and chiro-Configurations from 3-O-Benzyl-5,6-dideoxy-5-C-(1,3-dithian-2-yl)-6-nitro-d-galactofuranose and -l-altrofuranose

Abstract

Abstract The Michael addition of 2-lithio-1,3-dithiane to 3-O-benzyl-5,6-dideoxy-1,2-O-isopropylidene-6-nitro-β-l-arabino-hex-5-enofuranose afforded a 1 : 1.8 mixture of 3-O-benzyl-5,6-dideoxy-5-C-(1,3-dithian-2-yl)-1,2-O-isopropylidene-6-nitro-α-d-galactofuranose and-β-l-altrofuranose. Removal of the isopropylidene group and intra-molecular cyclization under weakly basic conditions afforded a mixture of branched-chain cyclitols having neo-, myo-, and chiro-configuration. A similar cyclization of the O-deisopropylidenated product of 3-O-benzyl-5,6-dideoxy-1,2-O-isopropylidene-6-nitro-5-C-(nitromethyl)-β-l-arabino-hexofuranose also afforded a mixture of cyclitols having neo-, myo-, and chiro-configuration. The results confirm the importance of two bulky groups such as benzyloxy at C-3 and 1,3-dithiane residue at C-5 in determining the stereodirection of cyclization.