Abstract: N-Allyl-2-methylaniline (12) forms on heating at 140° in xylene in the presence of zinc chloride 2-allyl-6-methylanline (19) as major compound and 4-allyl-2-methylaniline (20) as well as 2,7-dimethyl-indoline (21) as minor products. Compound 21 is also formed when 19 is heated in the presence of zinc chloride (scheme 2). That 19 arises from a charge-induced [3s, 3s] sigmatropic rearrangement of 12 – and 20 from two consecutive [3s, 3s]-sigmatropic transformations – follows from the reaction of N-crotyl-2-methylaniline (13) in the presence of zinc chloride at 140°. 2-(1′-Methylallyl)-6-methylaniline (22) and 4-crotyl-2-methylaniline (23) are formed exclusively. Small amounts of 2,3,7-trimethyl-indoline (24) and 2-(cis- and trans-1′-methyl-propenyl)-6-methylaniline (cis- and trans-25) are observed as by-products. Compound 24 arises from 22 in the presence of zinc chloride (scheme 3). Similar results are obtained when N-allyl and N-(2′-methylallyl)-N-methyl-aniline (14 and 15, respectively) are heated in the presence of zinc chloride. Whereas 14 gives nearly exclusively 2-allyl-N-methyl-aniline (28) and only small amounts of the corresponding 1, 2-dimethyl-indoline (29) and of 2-(cis- and trans-propenyl)-N-methyl-aniline (cis- and trans-27), 15 forms comparable amounts of 2-(2′-methylallyl)-N-methyl-aniline (30), 1,2,2-trimethyl-indoline (31), and 2-isobutenyl-N-methyl-aniline (32) (scheme 4). Compound 30, and also 32, are transformed into 31 on heating in the presence of zinc chloride.
Charge-induced aromatic amino-Claisen rearrangements are also observed when N-allylated anilinium tetraphenylborates are heated at 100–105° in hexamethyl phosphoric acid triamide. Thus, N-allyl- and N-crotyl-N, N-dimethyl-anilinium tetraphenylborate (16 and 17, respectively) yield 2-allyl- and 2-(1′-methylallyl)-N,N-dimethyl-aniline (33 and 34, respectively) besides small amounts of N, N-dimethyl-aniline. N-Cinnamyl-N, N-dimethyl-anilinium tetraphenylborate (18) gives, besides appreciable amounts of N,N-dimethyl-aniline, a mixture of 2-(1′-phenylallyl)-,2-cinnamyl-, and 4-cinnamyl-N, N-dimethyl-aniline (35, 36, and 37, respectively) in which the first two compounds predominate.