STEREOSELECTIVE ADDITION OF NITROMETHANE TO LEVOGLUCOSENONE - FORMATION AND STRUCTURE OF 2/1 AND 1/2 ADDUCTS

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.