Construction Of Vicinal Quaternary Carbon Centers Via Cobalt-Catalyzed Asymmetric Reverse Prenylation

Transition-metal-catalyzed allylic substitution reactions provide efficient ways to construct new carbon-carbon and carbon-heteroatom bonds.Palladium plays the most important role in this key transformation,but it usually produces linear products when unsymmetric allylic substrates are used for steric reason.Noble metals(Ir,Ru and Rh)catalyzed branched-selective allylation reactions were extensively studied.Nevertheless,there are still several problems to be solved,such as the quaternary carbon center formation as well as low reactivity and regioselectivity of aliphatic substituted allylic substrates.From the viewpoints of sustainable chemistry and economic concerns,earth-abundant first-row transition metals catalyzed asymmetric allylations are still very attractive.Cobalt,earth-abundant base metal,catalyzed allylic substitution is much less developed,although cobalt-catalyzed organic reactions have gained much attention recently.To the best of our knowledge,there is no cobalt-catalyzed highly enantioselective allylation substitution reaction reported before.On the other hand,stereoselective construction of vicinal all-carbon quaternary carbon centers is still very challenging in organic synthesis.By applying the allylic substitution strategy,very few examples were developed with transition-metals.Herein,we report the first highly enantioselective cobalt-catalyzed allylic substitution reaction.A highly enantioselective cobalt-catalyzed reverse prenylation of β-ketoester with tertiary allylic carbonate to construct vicinal all-carbon quaternary carbon centers has been developed.By using cobalt/(S,S)Ph-BPE complex generated in situ with zinc reduction,excellent branched to linear selectivity(> 20 : 1)and up to 92% ee have be obtained.