A [3 + 2] cycloaddition strategy to the phyllanthocin ring system

A general approach to methyleneoxabicyclo[n.3.0]alkyl heterocycles involves the intramolecular palladium catalyzed addition of trimethylsilylmethylallyl carboxylates to carbonyl groups. Such reactions require tin mediators and O,N-bis(trimethylsilyl)acetamide to prevent protodesilylation. Both 4-methylene-2-oxabicyclo[3.3.0]octane and 7-methylene-9-oxabicyclo[4.3.0]nonane have been produced. Whereas, the former is produced as a single diastereomer, the latter is produced as a mixture whose composition depends upon the presence of substituents. The core ring system of phyllanthocin has been produced in this way.