A stereocontrolled access to 9-methyl cyclobuta[a]indan: en route to rigid atipamezole analogues

This work deals with the preparation of a benzofused bicyclo[3.2.0]heptane intermediate en route to rigid analogues of atipamezole. We show that an intramolecular hydrosilylation in which a hydroxyl group serves as directing element can be used for the stereoselective synthesis of the target compound 7 from the exo-methylene derivative 4. The Si-H addition onto the proximal double bond is regioselective and the cyclization occurs exclusively via a 5-exo-trig mode. Although the γ-silyl alcohol 8a resisted 1,4-Brook-type rearrangement, its sodium salt was found to cyclize under thermal conditions to give the siloxacyclopentane 6a in good yield.