This report describes the development of a chiral Brønsted acid-catalyzed asymmetric MoritaBaylis À Hillman (MBH) reaction of cyclohexenone with aldehydes. During the course of our studies on chiral Lewis acid-promoted MBH reactions, we discovered that chiral binaphthol-derived Brønsted acids serve as promoters of the asymmetric MBH reaction. We propose that the phosphonium enolate of cyclohexenone is stabilized via hydrogen-bonding with the binaphthol-derived Brønsted acid, creating a chiral nucleophile. A practical and efficient set of conditions was developed using stoichiometric PEt 3 as the nucleophilic promoter and catalytic amounts of a binaphthol-derived Brønsted acid to effect the reaction of cyclohexenone with various aliphatic and aromatic aldehydes in good yields and enantiomeric excesses (up to 96% ee).

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Wählerische Ringe: Eine allgemeine Route zum Clerodan‐Diterpengerüst verläuft über eine asymmetrische Morita‐Baylis‐Hillman(MBH)‐Reaktion mit Lewis‐Säure‐vermittelten Anellierung. Bei der asymmetrischen Brønsted‐Säure‐katalysierten MBH‐Reaktion können auch Silylaldehyde umgesetzt werden, sodass Produkte mit einem trans‐Decalin‐Gerüst hoch diastereo‐ und enantioselektiv zugänglich sind.

Terpenes U 0200Efficient Construction of the Clerodane Decalin Core by an Asymmetric Morita-Baylis-Hillman Reaction/Lewis Acid Promoted Annulation Strategy. -The reaction conditions of the Morita-Baylis-Hillman reaction are mild enough to tolerate a variety of silane-containing aldehydes. The ring annulation conditions are effective for products (IIIa), (IIId) and (VI) and render possible the entry into the trans-decalin core of the clerodane diterpenes. -(RODGEN, S. A.; SCHAUS*, S. E.; Angew.

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