α‐Branched Ketone Dienolates: Base‐Catalysed Generation and Regio‐ and Enantioselective Addition Reactions

摘要: In this study, the unique capacity of bifunctional Bronsted bases to generate α-branched ketone dienolates and control both site- stereoselectivity their addition reactions representative classes carbon electrophiles (i.e., vinyl sulfones, nitroolefins, formaldehyde) is documented. We demonstrate that by using selected chiral tertiary amine/squaramide catalysts, β,γ-unsaturated cycloalkanones proceed through dienolate Cα almost exclusively provide all-carbon quaternary cyclic adducts in good yields with very high enantioselectivities. A minor amount (<5 %) γ-addition observed when nitroolefins are used as electrophiles. The parent acyclic proved be less reactive under these conditions, thus still constitute a challenging class substrates. Quantum chemical calculations correctly predict differences reactivity explain site-specificity enantioselectivity.