Pd-Catalyzed Microwave Irradiated Regioselective Aroylation Reaction of Crotyl- and Allyltrifluoroborates

An interesting regioselectivity is observed when the mixture of potassium crotyltrifluoroborate (1a) and aroyl chlorides having electron-deficient and electron-rich groups is microwaved in the presence of palladium-catalyst. In the case of electron withdrawing group with phenyl ring of aroyl chlorides, isomerized α,β-unsaturated compound 3 is the product whereas electron donating group with phenyl ring of aroyl chlorides furnishes α-adduct 4. Similar aroylation reaction is also established for potassium allyltrifluoroborate (1b). In this case, regioselectivity is unaffected with changing electron-rich or electron-deficient groups in phenyl ring of the aroyl chlorides. Reactions proceed with, essentially in same rate, affording the corresponding aryl propenyl ketones (crotonophenones) 5 in good to high yields.