Intramolecular Diels-Alder reactions of N-alkenyl-2(1H)-pyrazinones: generation of a novel type of cis-1,7-naphthyridine

The intramolecular Diels Alder reaction of three 1-(omega -alkenyl)-2(1H)-p yrazinones was investigated. Cycloaddition was shown to proceed for 1-(4-pe ntenyl)- and 1-(5-hexenyl)-2(1H)- pyrazinone 5a and 5b to give the correspo nding tricyclic hydrolysed adducts 7a and 7b, but not for the 1-(3-butenyl) derivative 5c. In contrast to 7b. the more strained 7a under,,vent selecti ve acidic solvolysis of the tertiary lactam group to give methyl cis-8-oxo- 6-phenyldecahydro[1,7]naphthyridine-6-carboxylate 8. An NMR analysis of 8 i s presented, (C) 2001 Elsevier Science Ltd. All rights reserved.