Vinyl benzenes as dienes in mild solid-phase Diels-Alder reactions

Wang resin-bound intermediates derived from Fmoc-L-phenylalaninal and Fmoc- L-valinal, and a resin supported Horner-Wadsworth-Emmons reaction, were tre ated with cinnamaldehyde derivatives, acetic acid, and borohydride to give secondary amines which were subsequently benzoylated to afford various deri vatives of 3. Heating 3 at 95 degrees C induced cycloaddition reactions and produced 4 as the major product. Compounds 3 which were derived from 4-met hoxycinnamaldehyde were more reactive, but did not give 4 and 4-7g. The dir ect cleavage of 3b using TFA led to the isolation of cycloaddition-demethyl ation product 10. The derivative of 3, which contained an electron-withdraw ing nitro group on the phenyl ring, produced a single diastereomer of 4. Th e Diels-Alder cycloaddition between two electron-deficient counterparts sho wed similar reactivity to that of the reactions which have a normal complem entary electron-demand.