Zinkchloridkatalysierte, thermische Umlagerungen von N‐Allyl in C‐Allyl‐aniline; ladungsinduzierte, aromatische Amino‐Claisen‐Umlagerungen

Abstract

AbstractN‐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.