Stereoselective addition of nitromethane to levoglucosenone; formation and structure of 2 : 1 and 1 : 2 adducts

Abstract

Tetramethylguanidine-catalysed addition of nitromethane to levoglucosenone affords in 98% yield a 10 : 1 mixture of 2 : 1 adducts 2 and 3, which result from initial Michael addition of nitromethanide exclusively from the exo face at C-4, followed by further reaction of the nitronate anion at both faces of the 1 : 1 adduct 4. In the presence of excess of levoglucosenone the major product (95%) is a pentacyclic 1 : 2 adduct 6, formed by reaction of 1 : 1 adduct 4 with further levoglucosenone. MeOH–levoglucosenone–MeNO₂ adduct 12 and 2 : 2 adduct 7 were also formed as by-products in the corresponding diethylamine-catalysed reaction in methanol. The structure of compound 6 was established by X-ray crystallography.