Intramolecular Diels-Alder reactions from trichloro-1,2,4-triazine and 1,5- and 1,6-dienes

Diels–Alder reactions of trichloro-1,2,4-triazine: intramolecular additions with 1,5 and 1,6 dienes

“…The present results provide clear cut support for the proposal that reaction of olefins with trichloro-1,2,4-triazine is initiated by Diels-Alder addition, with inverse electron demand, and loss of nitrogen to give a dihydropyridine followed by [1,5]sigmatropic hydrogen shift and HCl elimination to give a pyridine. With conjugated olefins like cyclopenta-1,3-diene and indene, the dihydropyridine ready undergoes a second Diels-Alder addition, and a suitably positioned olefin moiety can result in intramolecular Diels-Alder reaction.…”

“…Adoption of an anti-coplanar conformation for HC1 elimination is impossible, and the relative rigidity of the 12-membered ring hinders adoption of a syn-coplanar conformation, so aromatisation to give 30 is much slower than is, for example, observed with cyclododecene where addition to a C=C bond with the (E)- configuration appears favoured, like the case with cyclododecatriene, but where the absence of further double bonds makes the ring much more flexible. The configuration found for 31 is as expected for suprafacial addition to cyclododecatriene and a suprafacial [ 1,5]-hydrogen shift.…”

“…With hexa-1 ,5-diene, the dihydropyridine is trapped by an intramolecular Diels-Alder reaction, forming tricyclic compounds 17 and 18. With diallyl ether, the dihydropyridine partly undergoes intramolecular cycloaddition to give 23 and partly [ 1,5] -sigmatropic shift of hydrogen before intramolecular cycloaddition to give 25. With cyclododeca-1,5,9-triene formation of pyridine derivatives is incomplete and the immediate precursor can be trapped with water.…”

1,7-Dichloro-9-azatricyclo[4.3.1.03,7]decan-8-one, a hydrolysed Diels–Alder cycloaddition product from the reaction of 3,5,6-trichloro-1,2,4-triazine with hexa-1,5-diene

“…This structure determination is part of an investigation into the Diels-Alder addition of diolefms to trichloro-1,2,4-triazine (Barlow, Sibous & Tipping, 1992). The initial addition involving hexa-1,5-diene was regioselective, giving two intermediate products which underwent a second intramolecular addition to afford symmetrical compounds (3) (major) and (4) (minor), which were readily hydrolysed to the isolated amides, the title compound (I) and compound (2), respectively.…”

Allyl Ether

“…54,55 In these reactions, both double bonds undergo [4 + 2]-cycloaddition reactions in a stepwise manner. For instance, 4,5-dicyanopyridazine (15) reacts with diallyl ether in nearly quantitative yield to provide the tricyclic compound 16 (eq 9).…”