Substituent Effects on the Orientation of Diels-Alder Reactions. II

Abstract

The competitive ortho directing (c.o.d.) influence of a 1-methoxy group and a 4-methyl group and a 4-methyl was studied in the Diels–Alder addition of 1-methoxy-1,3-pentadiene (1) to 2,6-dimethylbenzoquinone (2). It was found that the c.o.d. influence of a terminally located methoxy is stronger than the effect of a terminal methyl group in the diene since only adduct 3 could be isolated. The influence of non-terminal substituents compared to terminal substituents in diene appears to be insignificant. This was demonstrated by obtaining only adduct 5 form the addition of 3-ethoxy-1,3-pentadiene (4) with 2,6-dimethylbenzoquinone (2). The following order of c.o.d. influence was suggested in the diene relative to a methyl group in the dienophile OCH3 > CH3 > H.