(−)-Sparteine-Mediated Asymmetric Cyclocarbolithiation of Alkenes Combined with a Stereospecificretro-[1,4]-Brook Rearrangement

A novel domino-type reaction sequence consisting of an enantioselective intramolecular carbolithiation of 6-phenylhex-5-enyl carbamates and a highly stereospecific retro-[1,4]-Brook rearrangement is reported. The carbocycles are formed with high enantiomeric (er >98 : 2) and diastereoisomer ratios (dr >99 : 1) in good yields (47 – 60%). On the basis of the absolute configuration of the cyclization products, a stereoretentive mechanism is proposed for the retro-[1,4]-Brook rearrangement.