Synthesis of Heterocyclic Antitumour Compounds Using Alkyne and Aryne Cycloadditions

The Diels-Alder reaction of α-pyrones with alkenes and alkynes is well known:1 some 40 years ago, Wittig and co-workers reported that the reaction of α-pyrone (1a) with benzyne (2) led to formation of naphthalene (4a).2 In fact, the initial adduct is the bicyclic intermediate 3a, which undergoes a retro-Diels-Alder reaction, losing CO2 to give the aromatic compound 4a. The intermediate 3a was not detected because its conversion to 4a is favoured on both enthalpic and entropic grounds. In the intervening years the synthetic potential of this transformation for construction of aromatic molecules from α-pyrones has hardly been exploited.3 Here we describe its application in the synthesis of some interesting compounds.