Enantioselective Catalytic Aldehyde α‐Alkylation/Semipinacol Rearrangement: Construction of α‐Quaternary‐δ‐Carbonyl Cycloketones and Total Synthesis of (+)‐Cerapicol

An enantioselective aldehyde α‐alkylation/semipinacol rearrangement was achieved through organo‐SOMO catalysis. The catalytically generated enamine radical cation serves as a carbon radical electrophile that can stereoselectively add to the alkene of an allylic alcohol and initiate ensuing ring‐expansion of cyclopropanol or cyclobutanol. This tandem reaction enables the production of a wide range of nonracemic functionalizable α‐quaternary‐δ‐carbonyl cycloketones in high yields and excellent enantioselectivity from simple aldehydes and allylic alcohols. As a key step, the intramolecular reaction was also successfully applied in the asymmetric total synthesis of (+)‐cerapicol. In tandem: An organocatalytic enantioselective aldehyde α‐alkylation/semipinacol rearrangement was developed with both inter‐ and intramolecular reaction variants. This tandem reaction provides efficient access to a wide range of enantioenriched α‐quaternary 1,5‐dicarbonyl compounds, the synthetic value is demonstrated by an asymmetric total synthesis of (+)‐cerapicol.