Pd-catalyzed ring opening of oxa- and azabicyclic alkenes with aryl and vinyl halides: Efficient entry to 2-substituted 1,2-dihydro-1-naphthols and 2-substituted 1-naphthols

[GRAPHICS] An efficient syntheses of 2-substituted 1,2-dihydro-1-naphthols and 2-substituted 1-naphthols has been developed that involves the sequential palladium-catalyzed ring opening of oxabicyclic alkenes with aryl and vinyl halides followed by oxidation of with IBX. In the first step of the sequence, a combination of Pd( OAc)(2), PPh3, Zn, and PMP in dry DMF was employed to catalyze the ring opening of 7-oxabenzonorbornadienes with aryl and vinyl halides to afford the corresponding cis-2-substituted 1,2-dihydronaphthols in good to excellent yields. These reactions occurred under very mild conditions with a variety of aryl halides bearing electron-withdrawing or -donating groups. Similarly, a 7-azabenzonorbornadiene substituted with an electron-withdrawing group on the nitrogen atom underwent facile ring-opening reaction with aryl halides to provide cis-2-substitued ( 1,2-dihydro-1-naphthyl) carbamates in excellent yields. Oxidation of the intermediate1,2-dihydro-1-naphthols using IBX yielded the corresponding 2-substituted 1-naphthols in good to excellent yields.