Catalytic synthesis of N-substituted allylarylamines

Abstract

Some N-substituted allylarylamines, for example, N-(1-methyl-2-butenyl) aniline (N-MBA) form, upon isomerization, not only ortho-, but also para- and 2,6-disubstituted derivatives, which does not fit into generally accepted theory. The amino-Claisen rearrangement (ACR) of N-MBA is catalyzed by Lewis acids, cationites, and arylamine hydrochlorides. This work presents the results of studies of ACR N-MBA in solutions of mineral acids. It was found that the reaction must be carried out in dilute solutions. At H2SO4 concentrations of 0.5 mol/L and below, three parallel reactions are observed with the formation of aniline, 2-(1-methyl-2-butenyl) aniline (2-MBA) and 4-(1-methyl-2-butenyl) aniline (4-MBA). The main product in all cases is 2-MBA, the content of which in the reaction mixture exceeds the amount of 4-MBA and aniline by 7 times, which are formed in approximately equal amounts. Prolonged refluxing of 2-MBA under the reaction conditions does not lead to its isomerization to 4-MBA, i.e., the para-isomer is formed directly from N-MBA. The formation of 2,6-di-(1-methyl-2-butenyl) aniline (DMBA) was not observed. In the presence of palladium catalysts, 2-MBA cyclizes to 2,4-methyl quinoline, which indicates the ortho-arrangement of its substituents; 4-MBA does not cyclize under these conditions. The obtained compounds are of interest in the synthesis of nitrogen-containing heterocycles and other polyfunctional organic compounds.