Stereoselective total synthesis of dihydrocorynantheol

A stereoselective synthesis of the indole alkaloid dihydrocorynantheol (1) from indole-3-acetic acid has been achieved by a sequence involing 9 as a key intermediate. The synthesis of the unsaturated lactam ring in 9 highlights a series of catalytic organometallic reactions featuring two ring-closing metatheses and a zirconocene-catalyzed carbomagnesation. Since no protecting groups were used, the present syntheses of 1 is exceedingly concise, consisting of only eight distinct operations.