Development of an additive-controlled, SmI(2)-mediated stereoselective sequence: Telescoped spirocyclisation, lactone reduction and Peterson elimination

Studies on SmI(2)-mediated spirocyclisation and lactone reduction culminate in a telescoped sequence in which additives are used to “switch on” individual steps mediated by the electron transfer reagent. The sequence involves the use of two activated SmI(2) reagent systems and a silicon stereocontrol element that exerts complete diastereocontrol over the cyclisation and is removed during the final stage of the sequence by Peterson elimination. The approach allows functionalised cyclopentanols containing two vicinal quaternary stereocentres to be conveniently prepared from simple starting materials.