Synthesis and thermal chemistry of isolevoglucosenone

Abstract

Isolevoglucosenone (1,6-anhydro-2,3-dideoxy-β- d- glycero-hex-2-enopyranos-4-ulose, 3) has been synthesized from levoglucosenone ( 2) in six steps. Thus, 1,6-anhydro-4- O-benzyl-3-deoxy-β- d- erythro-hexopyranos-2-ulose, obtained by Michael addition of benzyl alcohol to 2, was reduced with sodium borohydride to yield a separable mixture of the C-2 epimeric alcohols 1,6-anhydro-4- O-benzyl-3-deoxy-β- d- arabino- and - ribo-hexopyranose, both of which displayed intramolecular hydrogen-bonding. Acetylation, hydrogenolytic debenzylation, and pyridinium chlorochromate oxidation then led to the 2- O-acetyl-1,6-anhydro-hexos-4-uloses, from which 3 was obtained by tetraethylammonium acetate-catalyzed β-elimination of acetic acid. On sealed-tube thermolysis in the range of 210–260°, 3 generated 3-oxidopyrylium by loss of formaldehyde; this ylide was efficiently trapped by unreacted 3, to yield the [4 π + 2 π]-1,3-dipolar cycloadducts 14 and 15. The structure of 14 was fully elucidated by an X-ray crystallographic study. Neither 3 was, nor the adducts 14 and 15 were, detected among the products from acid-catalyzed pyrolysis of cellulose.