The[4+2]cycloaddition reaction between ortho-hydroxyphenyl-substituted para-quinone methides and ketimines was carried out in a phosphoric acid catalytic system.A wide range of dihydro-1,3-benzoxazine derivatives were obtained with good yields and excellent diastereoselectivities.When the catalytic amount of B(C6F5)3 was added to the reaction system,the yield of the product was maintained and the diastereoselectivity was flipped.
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