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Pauson–Khand Reaction of Allenic Hydrocarbons: Synthesis of 4‐Alkylidenecyclopentenones
Author(s) -
Antras Frédéric,
Laurent Stéphane,
Ahmar Mohammed,
Chermette Henry,
Cazes Bernard
Publication year - 2010
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200901224
Subject(s) - alkyne , allene , chemistry , pauson–khand reaction , stereochemistry , reaction mechanism , computational chemistry , medicinal chemistry , organic chemistry , catalysis , intramolecular force
The carbonyldicobalt‐mediated alkyne/allene/CO cocyclization gives 4‐alkylidenecyclopentenones as the major [2+2+1] cycloadducts. The regio‐ and stereoselectivities depend mainly on the substitution pattern of both the alkyne and the allenic moieties, which can be rationalized using the Magnus mechanism. However, contrary to this model, and in agreement with more recent mechanistic studies, our results provide evidence that both initial pseudo‐equatorial and pseudo‐axial coordination modes of the allenic hydrocarbons onto one of the cobalt atoms of the primary alkyne–dicobalt complex are involved. DFT calculations supporting both these coordination modes are given.