Chemistry of insect antifeedants from Azadirachta Indica (part 18): Demethylation and methylation of the C-8 position of the decalin portion of azadirachtin

Abstract The degradation of azadirachtin (1) to the demethylated decalin 4 and the subsequent remethylation to the protected fragment 5 are described. The crucial steps in the degradation sequence were the decarbonylation of 14 and the selective removal of the hydroxy group at C8 in 16. Reaction of the silyl enolether of 4 with Eschenmoser's salt and subsequent reduction of enone 24 gave 5.