OXIDATIVE CYCLIZATION OF 2-ALLYLPHENOLS BY PALLADIUM(II) ACETATE - CHANGES IN PRODUCT DISTRIBUTION

The cyclization of 2-allylphenols 1 having a cyclohexenyl moiety by an equimolar amount of Pd (OAc)2 in air (MeOH, 25 °C) gives a mixture of cis-1,2,4a,9b- and cis-1,4,4a,9b-tetrahydrodibenzofurans 3 and 4 in nearly equal ratio, together with a small amount of 2,3-butanobenzofuran 5. The addition of 9 equiv of cyclohexene to this reaction increases the proportion of 3 at the expense of those of 4 and 5. Further, the distribution of these products changes with changing the substrate concentration. In the presence of excess substrate, the major product is again 3. In the presence of O2 (~1 atm), the cyclization proceeds catalytically with respect to Pd (II) without using another cooxidant such as Cu (II), 0.5 molar equiv of O2 is constantly consumed for the catalytic production of 1 mol of cyclized products (3 + 4 + 5). On the basis of these results, the observed change in product distribution is interpreted in terms of alternation of reacting Pd(II) species involved in the reactions and interaction of intermediate Pd (II) complexes with olefins. In relation to the stereochemistry of the intermediate oxypalladation adduct, the metal-exchange reaction of the trans oxymercurials I and II has been examined by using palladium (II) acetate. © 1978, American Chemical Society. All rights reserved.