USE OF HINES-D-VALUES TO PREDICT THE POSITION OF THE EQUILIBRIUM IN THE COPE REARRANGEMENT OF MULTIPLY SUBSTITUTED 1,5-DIENES

A series of 1,5-dienes (1a-f) were employed to test whether Hine's D values can predict the position of equilibrium in Cope rearrangements. In the cases of the substituent pairs [OCH3, H], [OCH3, CH3], [N(CH3)(2), H], [N(CH3)(2), CH3], and [N(CH3)(2), OCH3], equilibrium constants calculated with Hine's D values gave reasonable agreement with those obtained experimentally. Dienes 1g-i were prepared to test whether reduction of the pi-donating character of a nitrogen substituent (carbamoyl vs dimethylamino) would change the directing ability of the nitrogen group. The aggregate order of directing ability was N(CH3)(2) > OCH3 > EtO(2)CN(CH3) > CH3 > A. Diene 15a, with a more complicated substitution pattern (OCH3 and CH3 versus CH3 and H) not directly amenable to analysis with D values, can be considered to reduce to the case of [OCH3, H]. The experimental K-eq obtained agreed with that expected for the [OCH3, H] pair. Dienes 15c and 16b, designed to test the pairs [CH3, SPh] and [OCH3, SPh], respectively, decomposed under the gas phase conditions of the rearrangement. Attempts to effect rearrangement with Pd(II) catalysis failed.