Conversion of the iridoid glucoside antirrhinoside into 3-azabicyclo[3.3.0]octane building blocks

The iridoid glucoside antirrhinoside (1) was transformed into polysubstituted 3-azabicyclo[3.3.0]octanes 3, 12, and 13 in 4 to 5 steps. Ozonolysis of the diacetonide of 1 and of its 7-deoxy-derivative 8 afforded cyclopentanoids 2 and 10, respectively. Conditions for the selective conversion of 2 and 10 into the corresponding ditosylates 4 and 11 were investigated. Cyclization of 4 and 11 was achieved with benzylamine and 2-methoxybenzylamine to yield bicyclic pyrrolidines 3, 12, and 13. Additional building blocks 14 and 15 were obtained by selective deprotection of the N-benzyl and isopropylidene moieties in 12 and 13, respectively.