Solid-Phase Synthesis of Linked Heterocycles

Significance

Resin-bound acrylic acid 1 prepared from polystyrene-supported selenenyl bromide reacted with amidoxime and dicyclohexylcarbodiimide to give the resin-bound 3-substituted 5-vinyl-1,2,4-oxadiazole 2 (eq. 1). The polymeric oxadiazole 2 reacted with nitrile oxide through 1,3-dipolar cycloaddition to give the resin-bound bicyclic product 3 which was followed by selenoxide syn elimination to give the substituted 5-(isoxazol-5-yl)-1,2,4-oxazole 4 (eq. 2). Azides also performed 1,3-dipolar cycloaddition with resin 2 to give substituted 4-(1,2,4-oxadiazol-5-yl)-1H-1,2,3-triazole 5. Substituted 5-(bicyclo[2.2.1]hepta- 2,5-dien-2-yl)-1,2,4-oxadiazole 6 and substituted 5-(4-methylcyclohexa-1,3-di­enyl)-1,2,4-oxadiazole 7 were obtained by expanding this method to a Diels-Alder reaction on resin 2 with cyclopentadiene and isoprene.