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Direct Umpolung Morita–Baylis–Hillman like α‐Functionalization of Enones via Enolonium Species
Author(s) -
Arava Shlomy,
Santra Sourav K.,
Pathe Gulab K.,
Kapanaiah Raja,
Szpilman Alex M.
Publication year - 2020
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.202005286
Subject(s) - umpolung , chemistry , electrophile , nucleophile , dabco , baylis–hillman reaction , medicinal chemistry , organic chemistry , lewis acids and bases , combinatorial chemistry , catalysis
Herein we report on the umpolung of Morita–Baylis–Hillman type intermediates and application to the α‐functionalization of enone C−H bonds. This reaction gives direct access to α‐chloro‐enones, 1,2‐diketones and α‐tosyloxy‐enones. The latter are important intermediates for cross‐coupling reaction and, to the best of our knowledge, cannot be made in a single step from enones in any other way. The proposed mechanism is supported by spectroscopic studies. The key initial step involves conjugate attack of an amine (DABCO or pyridine), likely assisted by hypervalent iodine acting as a Lewis acid leading to formation of an electrophilic β‐ammonium‐enolonium species. Nucleophilic attack by acetate, tosylate, or chloride anion is followed by base induced elimination of the ammonium species to give the noted products. Hydrolysis of α‐acetoxy‐enones lead to formation of 1,2‐diketones. The α‐tosyl‐enones participate in Negishi coupling reactions under standard conditions.