CYCLOADDITION REACTIONS OF 1,3-DIAZA-1,3-BUTADIENES WITH KETENES:SYNTHESIS AND CHEMICAL BEHAVIOUR OF 4-BENZYLIDENEAMINO-2-AZETIDINONES

Cycloaddition reactions of diazadienes have been extensively studied because of their importance in the synthesis of a wide variety of nitrogen containing heterocycles. In particular, [2+2] and [4+2] cyclo-addition reactions of 1,3-diaza-1,3-butadienes with ketenes could represent a versatile route for the synthesis of important beta-lactam derivatives as well as of different pyrimidinones. The beta-lactam skeleton is the key structural element of the most widely employed class of anti-bacterial agents. Moreover azeti-dinones are under active investi-gation in other pharmacological fields, as immunomodulators, neo-plasm inhibitors, anti-inflammatory, inhibitors of human leukocyte elastase, and inhibitors of choleste-rol absorption. Starting from 1,3-diazabuta-1,3-dienes 1a and 1b , never previously described in the literature, the research has been developed as follow: Step 1:Study on the behaviour of azadienes 1a and 1b in the cycloaddition reactions with mono and disubstituted ketenes.Step 2:Thermal and photochemical conversion of the beta-lactams derived from [2+2] cycloaddition of azadiene 1b into dihydro-pyrimidinones.Step 3:Stereoselective synthesis of 4-imino azetidinones starting from azadiene 1b and three different chiral ketenes: the menthoxyketene, the beta-silylalkylketene and the Evans-Sjögren ketene.