1,6-Anhydrofuranosen, XVIII. Wahlweise Cyclisieruhg Eines D-Allose-Deriyates Zur 1,6-Anhydrofuranose Oder Zum Furanoiden 1,6′:1,6-Dianhydrid

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Abstract
Depending on reaction conditions 1,2-Di-O-acetyl-3,5,6-tri-O-benzyl-D-allofuranose (2b) can be cyclized with SnCl4 either giving the monomeric 1,6-anhydrohexofuranose derivative 3a, as was already reported in a patent procedure, or by changing the solvent from methylene chloride to toluene giving the 1,6′:1′,6-dianhydride 4a mainly. The dimeric structure of compounds 4 was proved by CI-mass spectrometry. The 1H-n.m.r. spectrum of the acetate 4d allowed us to deduce the conformation preferentially adopted by these dianhydrides.