Synthesis of conjugated γ- and δ-lactones from aldehydes and ketones via a vinylation(allylation)-ring closing metathesis–oxidation sequence

Nucleophilic C-vinylation and C-allylation of aldehydes and ketones followed by O-allylation of the obtained carbinols gave the corresponding allyl or homoallyl ethers, respectively. Ring-closing metathesis of these compounds afforded in many cases cyclic ethers (dihydrofurans and dihydropyrans, respectively) bearing disubstituted and trisubstituted CC bonds. These were then subjected to allylic oxidation to yield conjugated γ- and δ-lactones. Reasons for the observed failures are presented and discussed.