A Nazarov‐Ene Tandem Reaction for the Stereoselective Construction of Spiro Compounds

The different reactivity of trienones under Lewis and Brønsted acids catalysis was investigated, resulting in distinct cyclization products and carbon backbones that originated either from a conjugate Prins cyclization or an interrupted Nazarov cyclization. In particular, an unprecedented Nazarov cy...

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Bibliographic Details
Published in:Chemistry : a European journal 2021-06, Vol.27 (36), p.9257-9262
Main Authors: Etling, Christoph, Tedesco, Giada, Kalesse, Markus
Format: Article
Language:English
Subjects:
Carbon cycle
Cascade chemical reactions
Catalysis
Chemistry
Communication
Communications
cyclization
Deuteration
domino reactions
ene reaction
Nazarov cyclization
Spiro compounds
Stereoselectivity
Substrates
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Summary:The different reactivity of trienones under Lewis and Brønsted acids catalysis was investigated, resulting in distinct cyclization products and carbon backbones that originated either from a conjugate Prins cyclization or an interrupted Nazarov cyclization. In particular, an unprecedented Nazarov cyclization tandem reaction is presented, terminating the oxyallyl cation by an ene‐type reaction, and leading stereoselectively to bicyclic spiro compounds. The terminal olefin of this motif represents a useful handle for further functionalization, making it a strategic intermediate in total syntheses. The tandem Nazarov/ene cyclization was shown to be preferred over a Nazarov/[3+2] tandem reaction for all our substrates, independent of chain length. Deuteration studies further support the mechanistic hypothesis of the terminating ene reaction. Investigations on Lewis‐ and Brønsted acid‐mediated cyclizations of trienones revealed a novel Nazarov cyclization/ene reaction tandem reaction. This reaction allows the stereoselective construction of quaternary spirocenters, with a β‐hydroxyl group acting as superb stereodirecting element. The produced spirocycles possess useful functionality for further modifications, making them potentially valuable synthetic intermediates.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.202101041