Preparation of 2-alkenylperhydro-1,3-benzoxazines and application for 2-isoxazolines synthesis

Abstract Various 2-substituted- N -benzyl-4,4,7-trimethyl- trans -octahydro-1,3-benzoxazines 2 were prepared from the condensation of (−)-8-benzylaminomenthol 1 derived from (+)-pulegone, with acrolein, crotonaldehyde, cinnamaldehyde, 2( E )- N , N -diisopropyl-4-oxobut-2-enamide, ethyl (2 E )-4-oxobut-2-enoate, and 2-furaldehyde in 71–96% yield. The 1,3-dipolar cycloaddition with aceto- and benzonitrile oxide gave the corresponding 2-isoxazoline cycloadducts. The origin of the stereoselectivity (4′ S , 5′ S- cycloadducts up to 64% de) arises from the cycloaddition of the dipole to the top of the Re,Re -alkene face of dipolarophile 2 .