The Rearrangement of Allyl Groups in Three-carbon Systems. IV. Hydrocarbons

Abstract

The following thermal rearrangement has been observed to occur in enough instances to establish the reaction as fairly general when X and JT are CN or COOC2H6'The allyl-type group has been shown to undergo inversion in two such cases, as indicated in the equation.2 This fact, together with first-order reaction kinetics and the observation that no interchange of migrating groups occurs when a mixture of two such compounds is heated, indicates that the rearrangement proceeds by an intramolecular cyclic mechanism.The influence of the groups, X and Y, is presumed to be derived from electron attraction, which enables the allyl group to release the electron pair binding it to the a-carbon atom. A conjugated double bond is formed in the a,,B-position while, a t the same time, the allyl group becomes attached in the y-position. Less strongly activated systems, in which the negative groups, X and U, are phenyl and nitrile groups or in which a single nitrile or carboxyl group is attached to the a-carbon atom, also undergo the rearrangement. The work now being reported was undertaken to find the least activation which would permit occurrence of the rearrangement.The hydrocarbons 111, V and VI1 have been synthesized and their behavior on heating has been determined. They rearranged at 165-185' in the manner shown in the following equations.(R = H or CHs) CfiHCCH-CH=CHg

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A computational study of the electron affinities of substituted Cope rearrangement transition states †

“…(1)]. [1][2][3] The list of authors who have examined this reaction in the nearly 60 years since it was discovered includes some of the top chemists in the field, and the elegant experimental methods one encounters illustrate the myriad of tools available for the investigation of reaction mechanisms. [4][5][6] Similarly, one sees the improvement of theoretical methods, beginning with semi-empirical 7,8 and small basis set selfconsistent field calculations, 9,10 progressing to multireference approaches, 9,11-14 and advancing through the latest density functional theory.…”