Anhydro ring opening

An exception to the generalized behavior in the anhydro-ring opening of furanosides is found in the reaction of methyl 2,3-anhydro-jS-n-lyxo-furanoside with sodium a-toluenethioxide.60 Surprisingly, predominant attack occurs at C-2, resulting in a 3 2 ratio of the 2-S-benzyl-2-thio- and 3-S-benzyl-3-thio-pentosides (isolated as the crystalline p-nitrobenzoates). 

Fig. 8. 1,6-Anhydro ring opening polymerization Stereospecific activated chain...

Treatment of benzyl 2-acetamido-3,4-anhydro-2-deoxy-6-C>-trityl-a-D-allopyranoside (412) with tetrabutylammonium fluoride [BU4NF in refluxing (refl.) MeCN, 24 h] gave, under diaxial ring-opening, benzyl 2-acetamido-2,4-dideoxy-4-fluoro-6-f9-trityl-a -D-gulopyranoside (413), in... 

Both the inner salts 6 of anhydro 177-[l,2,4]triazolo[4,3-6][l,2,4]triazolium hydroxides and their methylation products 7, when heated above the melting points, suffer loss of sulfur or of methyl iodide and sulfur, respectively, and concomitant ring opening into 1-methyl-3-methylthio-5 (arylcyanamino)[l,2,4]triazoles 8 takes place (Equation 1) <1984TL5427,1986T2121>. 

The same procedure was also applied to the synthesis of a-C-galactosyl compounds. Similarly, reductive ring opening of 1,2-anhydro sugar 93 with titanocene(m) chloride produces an anomeric radical 97 that can be trapped... 

Tri-0-acetyl-l,2-anhydro-a-D-glucose (Brigl s anhydride) can serve as a source of glycosides since the reactive expoxide ring opens perfer-entially at C-1 on alcoholysis, but contrary to expectations, a- as well as... 

Thiem et al. [21-23] studied the ring-opening polymerization of 1,4-anhydro-2,3-di-(9-alkyl-D-erythritols (4) using super-acids. 

With the nitrogen atom well protected as the cyclic carbamate 105, all attempts to open the 1,6-anhydro ring under acidic conditions failed owing to the lability of the two allylic benzyl ethers present in the molecule. However, it was possible to debenzylate 105 with lithium in ammonia to form the new cyclic carbamate 108 and acetylation then gave 109. 

Danilov and coworkers79 treated l,4 3,5-dianhydro-DL-xylitol with a number of primary and secondary amines. The 3,5-anhydro ring was opened, to give the corresponding 5-amino-5-deoxy compounds. 

For 1,4-anhydro-xylitol, ring opening was postulated to occur as follows ... 

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