Generation and Application ofo-Quinone Methides Bearing Various Substituents on the Benzene Ring

o-Quinone methides (o-QMs) are highly reactive, short-lived intermediates, which have potential synthetic applicability. However, few studies on the generation of o-QMs bearing an electron-withdrawing group have been reported. Herein we present a general method for the generation of o-QMs, particularly those substituted with an electrophilic substituent, from new precursors, 4H-1,2-benzoxazines 2. We have also studied systematically the Diels-Alder reactions of o-QMs with various dienophiles, such as vinyl ethers, enamines and imines. The reactions provide a versatile route to substituted chromans, phenols and 3,4-dihydro-2H-benzo[e]-[1,3]oxazines (3,4-dihydro-1,3-benzoxazines). Furthermore, we applied the new method to the derivatization of some natural products.