Abstract
The reaction of 2‐methyl‐2,3‐butadienoyl chloride 1 with the N‐aryl‐ or the N‐hetarylamines, 2a–f and 2g, h, respectively, in the ratio 1 : 2 (or 1 : 1 in the presence of triethylamine) furnishes the corresponding allenamides 3a–h, accompanied by the HCl adducts, the 3‐chloro‐2‐methyl‐3‐butenamides 4a–g, or the 3‐butynamide 5h. Heating of the allenamides bearing a benzenoid (3a–e) or thiophene (3h) nucleus does not generate any defined products; only the amides bearing the 1‐naphthyl (3f) and the furfuryl (3g) moiety undergo an intramolecular Diels‐Alder reaction to give the oligocyclic compounds 6 and 7. However, heating of the benzenoid allenamides 3a–c in the presence of tolyl isocyanate furnishes, via the N‐carbamoyl‐amides 10a–c, the intramolecular Diels‐Alder products 11a–c, whereby the monocyclic arene has functioned as diene. Reaction of 1 with the 2‐aminofuran derivative 2i leads directly to the Diels‐Alder product 9, a 2 : 1 adduct, whereby the initially formed amide 3i and the intramolecular Diels‐Alder product 8 are not isolated.