Glucal 1.2- dichloride

A tetraacetyl-2-desoxy-2-chloro-D-hexose (XV), which is shown to be homogeneous by its melting point and rotation, can be prepared in good yield from the mixture of triacetyl-D-glucal dichlorides by treatment with silver acetate in glacial acetic acid.3 Likewise, the mixture of... 

Tri-0-acetyl-l,5-anhydro-2-deoxy-D-arabino-hex-l-enitol (tri-O-acetyl-D-glucal) was the starting point for the synthesis of 1,5-anhy-dro-2-chloro-2-deoxy-D-glucitol or -D-mannitol by way of the 1,2-dichloride (22), which was reduced32 by means of lithium aluminum hydride to the 2-chloro-2-deoxy derivative (23). That the chlorine... 

Besides the D-glucose derivative just described, three other crystalline dichlorides have been prepared from 2-hydroxyglycals, namely, the dichlorides from 2,3,4,6-tetra-0-benzoyl-(2-hydroxy-D-glucal)10 (yield, 22%), 2,3,6,2, 3, 4, 6,-hepta-0-acetyl-(2-hydroxycellobial)IS (yield, 30%), and 2,3,4-tri-0-benzoyl-(2-hydroxy-D-xylal)12 (yield, 17%). The 2,3,4,6-tetra-0-benzoyl-l,2-dichloro-l-deoxy-D-hexose prepared from the first of these by short chlorination in benzene reacted with sodium acetate in hot, glacial acetic acid. The crystalline product was assigned the structure of l-0-acetyl-3,4,6-tri-0-benzoyl-D-glucosone10 since it is not converted to kojic acid by pyridine-acetic anhydride (see below). A benzoyl group has been lost. 

Osone hydrates have been prepared from 2,3,4,6-tetra-0-acetyl-(2-hydroxy-D-glucal)1 and from the corresponding derivatives of 2-hydroxy-D-galactal,9 2-hydroxyceIlobial13 and 2-hydroxygentiobial.13 Hydrolysis of the dichloride may be effected simply by the addition of a little water to its solution in ether or benzene, but more often silver carbonate or sodium bicarbonate is added to neutralize the hydrogen chloride produced. Sodium and potassium carbonate are too alkaline and result in yellowing of the reaction mixture. A yield of 90% of the theoretical amount of osone hydrate was obtained from the crystalline dichloride derived from D-glu-cose. However, the crystalline dichloride derived from cellobiose resisted hydrolysis (see the previous Section). Nevertheless, the cellobiosone hydrate was prepared from the sirupy mother liquor. In any case, yields on the basis of the entire, chlorinated substances were low.1613... 

Chlorine can add to the double bond in triacetyl-D-glucal in a manner similar to that of bromine.311 The resulting dichlorides (XIV) have more tendency to crystallize than the dibromides. However, many of the... 

Preparative TLC has afforded the two pure isomeric dichlorides obtained by addition of chlorine to tri-O-acetyl-D-glucal. The capacity of silica gel G plates is favorable for preparative purposes. The 250 [x thick layers (20 x 20 cm plate) permitted separation of 25 mg of the mixture of dichlorides with the solvent toluene-ether (67 + 33) [89]. Tate and Bishop [84] report the separation of up to 100 mg of the benzylated sugars on one plate. 

Another synthesis of the ciguatoxin A/B ring system has been prepared from tri-O-acetyl-D-glucal from which 209 was made. Lithium Tms acetylide substitution, replacement of the 04 ethoxyethyl with acetate and anomeric deoxygenation gives 210. Titanium dichloride-catalysed reaction with ZRAS-... 

---