Mechanism of Remote Conjugate Addition of a Lithium Organocuprate to a Polyconjugated Carbonyl Compound

✍ Scribed by Naohiko Yoshikai; Tatsuya Yamashita; Eiichi Nakamura

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 350 KB
• Volume: 117
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/ange.200501107

✦ Synopsis

Conjugate addition [1] of a nucleophile to a polyconjugated carbonyl compound is an intriguing reaction as it can potentially result in CÀC bond formation at one of the remote carbon atoms. In many cases, however, the regioselectivity may be poor, unpredictable, or condition-dependent, and the origin of the regioselectivity often difficult to determine with certainty. [2,3] The particular combination of a polyenynyl carbonyl compound A and a lithium organocuprate is unique in all respects in that the CÀC bond formation takes place always at the remote acetylenic carbon atom to give an adduct D (Scheme 1). [4,5] Although important pieces of information-NMR spectroscopic identification of the reaction intermediate and the activation energy of the reaction-have been reported, [4b,c] they do not give an answer to the fundamental question as to why the cuprate addition takes place at the acetylene terminal. We report herein a density-functional study on the reaction pathway and the origin of the regioselectivity of this reaction. [6] Scheme 1. Regioselective conjugate addition of a lithium organocuprate to a polyenynyl carbonyl compound.