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

Abstract

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 [3 s , 3 s ] sigmatropic rearrangement of 12 – and 20 from two consecutive [3 s , 3 s ]‐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.