Der Mechanismus der Umlagerung substituierter Aminoacrylderivate

Thioacetic acid and dithioacetic acid react with alkynederivatives of the type (CH 3 ) 2 NCCCOR ( 1 ) in the same way as other carboxylic acids: The addition to dimethylaminopropinal ( 1a ) at low temperatures yields, after rearrangement of the very instable primary adducts, Z ‐3‐acetoxy‐N,N‐dimethyl‐thioacrylamide ( Z ‐16 ) and Z ‐3‐thioacetoxy‐N,N‐dimethylthioacrylamide ( Z ‐17 ) respectively. The structure of the two compounds can be proved by spectroscopic evidence of 16 and 18 , the latter being formed by elimination of thioketene from 17 . According to the distribution of S‐atoms in 16 and 17 , two reaction pathways including 4‐membered rings can be ruled out. Thus the rearrangement of 3‐acyloxy‐N,N‐dimethyl‐acrylamides most probably proceeds by a mechanism including a dipolar six‐membered intermediate. This mechanism cannot be valid for the rearrangement of the adducts 2 of hydrohalogen acids, alcohols and amines to the alkyne‐derivatives 1 . The acid‐catalysed reaction of 3‐chloro‐3‐dimethylamino‐propenal ( 2 , XCl), labelled at position 1 with 13 C, yields 3‐chloro‐N,N‐dimethyl‐acrylamide ( 3 , XCl), containing the label exclusively at position 3 . This result supports a mechanism including an immonium‐oxetene 21 (XCl) as intermediate. ‐ The experiments are in accord with kinetic investigations.