THE REACTION OF UNSATURATED CARBOHYDRATES WITH CARBON MONOXIDE AND HYDROGEN: IV. STRUCTURE AND STEREOCHEMISTRY OF ANHYDRODEOXYHEPTITOLS FROM 3,4,6-TRI-O-ACETYL-D-GALACTAL

Abstract

3,4,6-Tri-0-acetyl-D-galactal reacted with carbon monoxide and hydrogen in the presence of dicobalt octacarbonyl t o yield 2,6-anhydro-3-deoxy-D-galado-heptitol (I) and 2,6-anhydro-3-deoxy-D-lalo-heptitol (11). The stereochemistry of (I) and (11) has been established by correlation with 2,6-anhydro-3-deoxy-D-gluco-heptitol (VI) of lcnown configuration. Evidence that both (I) and (11) are formed by the addition of a hydroxmethyl group t o C-1 of the glycal is also furnished by the proton 1l.m.r. spectra of the normal and deuterated anhydrodeoxyheptitols.Part I of this series (1) described the action of carbon monoxide and hydrogen on 3,4,6-tri-0-acetyl-~-galactal, and presented evidence for the formation of a n anhydrodeoxyheptitol of unknown stereochemistry. I t has since been found t h a t 3,4,6-tri-0-acetyl-D-galactal reacts under 0x0 conditions in a manner entirely analogous t o other glycals investigated (2,3) to yield a s the major products a pair of isomeric anhydrodeoxyheptitols (I) and (11), formed by the addition of a hydroxymethyl group to C-1 of the unsaturated carbohydrate. The stereochemistry of (I) and (11) has been elucidated by a n analysis of their proton n.m.r. spectra and by correlation with 2,6-anhydro-3-deoxy-D-gbco-heptitol (VI), whose structure has been proved by crystallographic X-ray analysis (4).3,4,6-Tri-0-acetyl-D-galactal (5) was reacted in a high-pressure apparatus with carbon monoxide and hydrogen in the presence of dicobalt octacarbonyl, under conditions similar to those described previously (1). The reaction product was separated from the catalyst by chromatography on a Florisil column, and deacetylated with methanolic sodium methoxide. The two major reaction products (I) and (11), after separation by preparative paper chromatography, were obtained in approximately equal amounts. DISCUSSION Both (I) and (11) consumed 1 molar equivalent of periodate (0.95 and 0.98 respectively) as measured by the spectrophotometric method of Dixon and Lipkin (6). Fraction (11) reacted with acetone in the presence of sulfuric acid to form a monoisopropylidene derivative (VII), which on treatment with p-toluenesulfonyl chloride in pyridine gave a compound (VIII) containing two tosyloxy groups. The latter compound on heating with sodiunl iodide in acetone solution liberated 2 equivalents of sodium p-toluenesulfonate. Thus i t is highly likely t h a t (11) contains two primary hydroxyl groups and two adjacent cis secondary hydroxyl groups. Compound (I) was characterized as the tetra-0-(p-nitrobenzoyl) derivative.Evidence that both (I) and (11) have unbranched carbon skeletons was furnished by their proton nuclear magnetic resonance (n.m.r.) spectra, measured in DzO solution (Fig. l a and c). These both show a group of signals a t lower field (3.3-4.3 p.p.m.) with total area corresponding t o 8 hydrogens, and a further group a t higher field (1.3-2.3 p.p.m.), area = 2 hydrogens. The higher field signals can clearly be assigned t o hydrogens attached