INTRAMOLECULAR PYRONE/PYRIDONE (4+4) PHOTOCYCLOADDITIONS

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The photochemical [4+4] dimerization of 2-pyrones and 2-pyridones is a potentially powerful method for construction of highly functionalized cyclooctanes. This reaction assembles two achiral, readily prepared, aromatic molecules into a 1,5-cyclooctadiene with four stereogenic centers and a terpene skeleton. An unprecedented intramolecular version of ths reaction would allow this transformation to be harnessed for the synthesis of complex, eight- membered ring natural products, many of which are associated with important biological activity (e.g., antitumor, antibiotic, etc.). In a preliminary study (1), a solution of a bis-pyridone with a three atom tether was irradiated. Only one major product, resulting from a [4+4] cyclization (greater than 80% yield, 100% conversion), was observed, indicating that the alcohol on the tether had strongly influenced the formation of four new stereogenic centers. The initial goal of this project is to explore the scope of this untested intramolecular reaction, emphasizing features which are important for synthetic applications such as tether length and stereoinduction. A study of the chemistry of the [4+4] product, in the context of models and total synthesis, will form the second stage of the investigation.