Claisen‐Umlagerung von 2‐Propinyl‐(3‐pyridyl)‐und Allyl‐(3‐pyridyl)äthern

Claisen Rearrangement of 2‐Propinyl (3‐Pyridyl) and Allyl (3‐Pyridyl) Ethers Verbindungen vom Typ 1 werden mit Ausnahme von 17 und 25 als Äther benannt. Der systematische Name von 1 ist: 3‐(2‐Propinyl)oxy‐pyridin. 2‐Propinyl (3‐pyridyl) ether (1), synthesized from the corresponding 3‐pyridinol, was heated in DMF or decane at 208° in a sealed tube. In this way the furopyridines 2 and 3 were formed, and furthermore the pyranopyridine 4 if decane was used as solvent (Scheme 1). The same reactions took place with (2‐methyl‐3‐pyridyl) 2‐propinyl ether (14). In DMF only 15, and in decane 16 as well as 15 were formed (Scheme 3). The rearrangement of the pyridine derivative 17, which is substituted in both O‐positions to the ether moiety, gave in both DMF and decane the diastereoisomeric tetracyclic compounds 18 and 19. The same kind of reaction took place with 25 (Scheme 4). In the thermolysis of the allyl 3‐pyridyl ether (27) cyclization was observed, too. The isolated product has the structure of the dihydrofuropyridine 28 (Scheme 6). The substituted allyl 3‐pyridyl ether 30 reacted in the same way to the dihydrofuropyridine 31 (Scheme 6).