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Mechanism of Remote Conjugate Addition of Lithium Organocuprates to Polyconjugated Carbonyl Compounds
Author(s) -
Yoshikai Naohiko,
Yamashita Tatsuya,
Nakamura Eiichi
Publication year - 2006
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.200600034
Subject(s) - chemistry , regioselectivity , reductive elimination , conjugate , lithium (medication) , conjugated system , reaction mechanism , density functional theory , photochemistry , reaction intermediate , addition reaction , computational chemistry , stereochemistry , organic chemistry , catalysis , mathematical analysis , mathematics , medicine , polymer , endocrinology
Regioselective reaction of a lithium organocuprate (R 2 CuLi) and a polyconjugated carbonyl compound affords a remote‐conjugate‐addition product. This reaction proceeds particularly cleanly when the conjugation is terminated by a CC triple bond. The reaction pathways and the origin of the regioselectivity of this class of transformations are explored with the aid of density functional calculations. The outline of the reaction pathway is as follows. An initially formed β‐cuprio(III) enolate intermediate undergoes smooth copper migration along the conjugated system. This process takes place faster than reductive elimination of intermediary σ/π‐allylcopper(III) species, since the latter reaction disrupts the conjugation in the substrate and hence is not preferred. The copper migration to the acetylenic terminal affords a σ/π‐allenylcopper(III) intermediate, which undergoes facile and selective CC bond forming reductive elimination at the terminal carbon atom. The present mechanistic framework shows good agreement with some pertinent experimental data, including 13 C NMR chemical shifts and kinetic isotope effects.