A new method for generation and intramolecular diels-alder reaction of N-acyl and N-alkoxycarbonyl-1-aza-1,3-butadibnes. A one-pot synthesis of 1,7,8,8a-tetrahydro-3(2H)-indolizinones and 1,2,3,8,9,9a-hexahydro-4(4h)-quinolinones from α,β-unsaturated aldehydes