Regioselectivity in cycloaddition reactions on solid phases

A 1% crosslinked divinylbenzene-styrene copolymer, incorporating benzyl acrylate groups, reacted in normal Diels–Alder reactions with E-1-phenyl-1,3-butadiene or methyl E-2,4-pentadienoate to give their respective polymer-bound benzyl cyclohexenecarboxylates. Polymer-bound benzyl propiolate and polymer-bound benzyl phenylpropiolate reacted with benzonitrile oxide in a typical 1,3-dipolar addition reaction to give their respective polymer-bound isoxazoles. Cleavage of the polymer-bound Diels–Alder adducts and the polymer-bound 1,3-dipolar addition adduct derived from polymer-bound benzyl propiolate gave mixtures of ortho and meta regiomers similar to those produced in analogous reactions in solution. Cleavage of the polymer-bound 1,3-dipolar addition adduct, derived from polymer-bound benzyl phenylpropiolate, followed by esterification, gave a solitary adduct, 4-carbomethoxy-3,5-diphenylisoxazole, but an analogous solution 1,3-dipolar addition yielded a 1:1 ratio of the two possible regiomers.