An enantioselective synthetic method to access substituted indenes by chiral Brønsted catalyzed Nazarov-type cyclization of β-amino-1,4-enynols is described. The catalytic protocol allows access to a variety of enantioenriched indene derivatives in up to 99% yield and up to 99% ee value. A combined experimental and computational study supports a mechanism involving dehydration of the 1,4-enynol to generate a pentadienyl cation intermediate, which then engages in a 4π-electrocyclization to form the desired product. A dual mode of interaction involving hydrogen bonding and ion pairing between the pentadienyl cation and the phosphoramide anion is thought to account for the observed product enantioselectivities.

Enantioselective synthesis indenes via chiral Brønsted acid catalyzed Nazarov-type cyclization of β-amino-1,4-enynols

253rd National Meeting (2017)

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