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Cobalt(I)‐Mediated Preparation of Polyborylated Cyclohexadienes: Scope, Limitations, and Mechanistic Insight
Author(s) -
Geny Anaïs,
Lebœuf David,
Rouquié Gabriel,
Vollhardt K. Peter C.,
Malacria Max,
Gandon Vincent,
Aubert Corinne
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700337
Subject(s) - steric effects , chemistry , regioselectivity , cycloaddition , intermolecular force , cobalt , alkyne , combinatorial chemistry , medicinal chemistry , stereochemistry , organic chemistry , catalysis , molecule
A series of 1,3‐ and 1,4‐diboryl‐1,3‐cyclohexadienes have been prepared by intermolecular CoCp‐mediated [2+2+2] cocyclizations of alkynylboronic pinacolate esters with alkenes, followed by oxidative demetallation with iron(III) chloride. The effect of substitution at the borylated alkyne on chemo‐ and regioselectivities has been studied, suggesting steric control. The proper choice of substituents allowed the preparation of 1,3‐diborylated cyclohexadienes in a highly selective manner. Alternatively, 1,4‐diborylated cyclohexadienes could be prepared from diborylated diynes. The scope of this reaction has been examined and found to include electron‐poor, electron‐rich, linear, and cyclic alkenes. The diborylated cyclohexadienes were submitted to single or double Suzuki–Miyaura cross‐coupling reactions with haloarenes to afford polyarylated systems. The mechanism of the title reaction, including the regioselectivity of the cycloaddition steps, has been analyzed by means of DFT computations.