Halogeno, Thio, and Deoxy Derivatives of 1,6-Anhydrohexopyranoses

Of the halogenated 1,6-anhydrohexopyranoses, the main interest has been directed to the iodo derivatives384,630-632 as intermediates for the synthesis of deoxy sugars, and to the fluoro derivatives (for a review, see Ref. 773), interesting from both the chemical and the biochemical point of view. The chloro and bromo derivatives have been examined only rarely.94,168,319,437 

The syntheses of the title compounds start mostly from 1,6-anhydro derivatives, using either the often regioselective course of the oxi-rane-ring opening by nucleophilic agents380,384,437,447,448,506 507,544,629,630,632 637 (see Sect. V), or the Sn2 replacement.632 Cyclization of deoxyhalo- 

The reaction of 26 with bromine in carbon tetrachloride yields325-327 a mixture of exo and endo bromo derivatives (27) in the ratio of 3 2 (see also, Section 11,7). The supposed intermediate of this acetal bromination into the 2-position is326 3,4-dihydro-2H-pyran-2-methanol (25) however, direct conversion of 25 into 27 was not demonstrated. 

Compound 180 was converted by way of a redox sequence, into l,6-anhydro-4-deoxy-4-iodo-2-0-p-tolylsulfonyl-j8-D-allopyranose757 (182). Iodine in ketone 181 can be very readily eliminated by reduc- 

The fluoro derivatives of 1,6-anhydrohexopyranoses undergo all of the common reactions of 1,6-anhydrohexoses. By using a redox sequence, derivatives of l,6-aiihydro-/3-D-allopyranose were prepared545 from 183 and 185. Ammonolysis of the fluoro epoxide 184 leads to the amino derivative381 190, and hydrogenolysis of 184 gives 

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