The palladium-catalyzed coupling reaction of iodophenols (1) with 2-methyl-3-butyn-2-ol gave alkynylphenols (2). Catalytic hydrogenation of 2 over Raney nickel and the subsequent dehydration of the resultant alkylphenols (3) gave regioselectively the desired prenylphenols (4). Dehydration of alkylphenols (3f-h) gave chromans (7).
Cyclization of o-(3-Hydroxy-3-methylbutynyl)phenols with Boron Tribromide to 4-Bromo-2,2-dimethylchromenes and Their Electroreduction to 2,2-Dimethylchromenes
Cyclization of o-(3-hydroxy-3-methylbutynyl)phenols (2) with boron tribromide gave easily 4-bromo-2,2-dimethylchromenes (3). Electrolytic reduction of 3 at a Hg-pool electrode afforded the corresponding 2,2-dimethylchromenes (6) in high yields.