3.6- anhydro-D-glucal

SCHEME 12.2 Formation of a 3,6-anhydro-D-glucal with benzylation reaction conditions. 

PREPARATION OF 3,6-ANHYDRO-d-GLUCAL UNDER REDUCTIVE CONDITIONS... 

In fact, when the anhydroglucal 7 was placed in anhydrous acetonitrile with NIS and only activated 4 A molecular sieves, an improved yield of 76% ofdianhydrosugar 9 was obtained. Previously, Brimacombe and colleagues observed the formation of similar dianhydrosugar when the 3,6-anhydro-D-glucal 7 was left in anhydrous... 

FIGURE 12.2 Reaction of 3,6-anhydro-D-glucal 7 with CAN and thiophenol with and without added sodium iodide. 

Di-Ac 3,4-Di-0-acetyl-6-amino-l,5-anhydro-6-deoxy-D-nidb no-hex-l-enitol. 3,4-Di-0-acetyl-6-amino-6-deoxy-D-glucal... 

N-Tri-Ac 6-Acetamido-3,4-di-0-acet-yl-I, S-anhydro-d-deoxy-D-atab mo-hex-1-enitol. 6-Acetamido-3,4-di-0-acetyl-6-deoxy-D-glucal [117136-29-5]... 

Di-0-benzyl-6-deoxy-6-fluoro-D-glucal has been synthesized from 6-0-t-butyldimethylsilyl-D-glucal by the route shown in Scheme 56. This route was devized because a seemingly more direct route involving benzylation of 6-0-toluene-p-suIphonyl-D-glucal gave the 3,6-anhydro-derivative (213). More-... 

Unsaturated sugars are useful synthetic intermediates (11). The most commonly used are the so-called glycals (1,5- or 1,4-anhydroalditol-l-enes). In the presence of a Lewis-acid catalyst, 3,4,6-tri-0-acetyl-l,5-anhydro-2-deoxy-D-arabinohex-l-enitol [2873-29-2] commonly called D-glucal triacetate, adds nucleophiles in both kineticaHy controlled and thermodynamically controlled (soft bases predominately at C-3 and hard bases primarily at C-1) reactions (11,13). 

In 1969, Adamson, Foster, and others - reported the synthesis of 2-deoxy-2-fluoro sugars by addition ofCFjOF (in CFCI3, — 80°) to 3,4,6-tri-O-acetyl-l,5-anhydro-2-deoxy-D-flra/)/>zo-hex-l-enitol (61 3,4,6-tri-O-acetyl-D-glucal). The reagent fluorinates 61 electrophilically - °° at C-2, to afford c/v-addition products trifluoromethyl 3,4,6-tri-C)-acetyl-2-deoxy-2-... 

On their side, Yin and Linker [216] made use of a 2-C-branched hexopyranoside, the synthesis of which was achieved by addition of dimethyl malonate to tri-O-benzyl-D-glucal (TUPAC name 3,4,6-tri-0-benzyl-l,5-anhydro-2-deoxy-D-araZtino-hex-l-enitol, Scheme 45) [217], Thus, saponification of the 2-C-[bis(meth-oxycarbonyl)]methyl derivative 184 to the corresponding malonic acid 185 was followed by heating in refluxing toluene. This led to decarboxylation and lactoniza-tion giving 186. The method was optimized and applied to the synthesis of pentoses and disaccharides. 

Previously, the reaction of 3,4,6-tri-0-acetyl-l,5-anhydro-2-deoxy-D-arabino-hex-l-enitol (D-glucal triacetate) (20) with lead thiocyanate in a mixture of acetic acid, acetic anhydride, and carbon tetrachloride had been reported by Igarashi and Honma.37 They observed formation of isothiocyanate 21 as the main product, accompanied by a mixture of four isomeric thiocyanates. 

Somewhat surprisingly, particularly in view of the proposed means of formation of the glycosid-3-ulose derivative 2,1,5-anhydro-2,3,4,6-tetra-O-benzoyl-D-arah/no-hex-1 -enitol (tetra-O-benzoyl-2-hydroxy-D-glucal) does not undergo bromination at the allylic C-3 atom the only products isolated following attempted photobromination with N-bromosucdnimide were two dibromides produced by addition reactions.50... 

Tetra-0-acetyl-(2-hydroxy-D-glucal) has been compared with several other anhydro-sugars with respect to absorption spectra and heats of combustion.42... 

---