Abstract: A synthesis of the tetracyclic decalin part of azadirachtin in the naturally occurring form is described. The key reactions involve the Corey-Bakshi-Shibata (CBS) asymmetric reduction of the ketone, and an intramolecular Diels-Alder (IMDA) reaction. Key words: azadirachtin, insect antifeedant, decalin, CBS asymmetric reduction, intramolecular Diels- Alder reaction