172508-29-1Relevant articles and documents
Cobalt- and Silver-Promoted Methylenecyclopropane Rearrangements
Creary, Xavier
, p. 136 - 144 (2018/02/19)
The rate of the methylenecyclopropane rearrangement is enhanced by an alkyne-Co2(CO)6 complex bonded to the para position of a benzene ring. This is explained by a stabilizing effect on the transition state leading to the biradical intermediate. Computational studies indicate that the benzylic-type biradical intermediate is stabilized by a delocalization mechanism, where spin is delocalized onto the two cobalt atoms. Silver cation also enhances the rate of the methylenecyclopropane rearrangement. Computational studies suggest that silver cation can also stabilize a benzylic radical by spin delocalization involving silver. In the case of the silver-promoted reactions, the rate enhancements in a series of aryl-substituted methylenecyclopropanes correlate with σ+ values. The question remains open as to whether the silver-catalyzed methylenecyclopropane rearrangement proceeds via an argento-stabilized biradical or whether the reaction involves an argento-substituted allylic cation.
Highly Active Trialkoxymolybdenum(VI) Alkylidyne Catalysts Synthesized by A Reductive Recycle Strategy
Zhang, Wei,Kraft, Stefan,Moore, Jeffrey S.
, p. 329 - 335 (2007/10/03)
A systematic study of alkyne metathesis catalyzed by trialkoxymolybdenum(VI) alkylidyne complexes is reported, in which substrate functional groups, alkynyl substituents, and catalyst ligands are varied. Sterically hindered trisamidomolybdenum(VI) propylidyne complex 5 was prepared conveniently through a previously communicated reductive recycle strategy. Alcoholysis of 5 with various phenols/alcohols provides a set of active catalysts for alkyne metathesis at room temperature, among which the catalyst with p-nitrophenol as ligand shows the highest catalytic activity and is compatible with a variety of functional groups and solvents. A key finding that enabled the use of highly active molybdenum(VI) catalysts is replacement of the commonly used propynyl substituents on the starting alkyne substrates with butynyl groups. Under reduced pressure using 1,2,4-trichlorobenzene as an involatile solvent, the alkyne metathesis of butynyl substituted compounds proceeds well at 30 °C providing high yields (83%-97%) of dimers. Rationalization of the special role played by butynyl substrates is discussed.
Alkyne metathesis with simple catalyst systems: High yield dimerization of propynylated aromatics; scope and limitations
Pschirer, Neil Gregory,Bunz, Uwe H. F.
, p. 2481 - 2484 (2007/10/03)
High yield dimerization of propynylated benzenes and propynylnaphthalene by a mixture of Mo(CO)6 and 4-chlorophenol at 140 °C in 1,2-dichlorobenzene is reported to give the corresponding disubstituted alkynes. The scope and limitation of the reaction and the influence of substitution pattern and substitution type are discussed. Oxygen or nitrogen carrying substrates metathesize in moderate to good yields and ortho-alkyl substituted examples form the respective tolanes very efficiently.
Palladium-Catalyzed Arylation of Polar Organometallics Mediated by 9-Methoxy-9-Borabicyclononane: Suzuki Reactions of Extended Scope
Fuerstner, Alois,Seidel, Guenter
, p. 11165 - 11176 (2007/10/02)
An alternative way for performing Suzuki reactions is presented.The necessary borate is the actual nucleophile in these palladium catalyzed C-C-bond formations is prepared from 9-methoxy-9-borabicyclononane (9-OMe-9-BBN) and a polar organometallic reagent RM, and not as usually from a borane and a base.This approach allows cross couplings of aryl halides with e.g. alkynyl-, methyl-, or TMSCH2-groups, which were beyond the scope of the conventional Suzuki reaction.The method is highly chemoselective and turned out to be compatible with aldehyde-, amide-, ketone-, ester- and cyano functions as well as with basic nitrogen atoms in the substrates.It was applied to the synthesis of the acetylenic natural products junipal (9a) and eutypine methyl ether (10).Since 11B NMR studies revealed that the 9-OMe-9-BBN only serves as a shuttle for delivering the RM reagent but remains unchanged during the course of the reaction, it has been possible to device the first Suzuki-type reaction sub-stoichiometric in boron.This "catalytic" protocol was used to prepare compound 8 which is highly valuable for its chemoluminescence properties.
