A ruthenium catalyst for Z-selective olefin metathesis has been synthesized from a readily accessible N-heterocyclic carbene (NHC) ligand that is prepared thanks to an efficient, practical and scalable multicomponent synthesis. The desired ruthenium complex with cyclometalated NHC ligand is obtained by means of selective C(sp 3)-H activation at the adamantyl fragment and X-ray diffraction analysis unambiguously confirmed the structure of the precatalyst. The catalyst demonstrated attractive catalytic performance in self-and cross-metathesis at low catalyst loading to afford the desired internal olefins with high conversion and very high Z-selectivity (up to >99%). The versatility of the chelated catalyst is illustrated by the high cis-selectivity (up to >98%) and high tacticity control (up to >98% syndiotactic) achieved in ring-opening-polymerization, allowing for the production of highly microstructurally controlled norbornene, norbornadiene and cyclopropene-derived polymers.
A new multicomponent procedure was applied to the synthesis of (a)chiral bulky unsymmetrical unsaturated 2,6-diisopropylphenyl-N-heterocyclic carbene (NHC) precursors with excellent selectivity (up to 95%) and good yields. This approach offers access to new chiral NHCs ligands, which found successful applications in both copper-catalyzed asymmetric allylic alkylation and coppercatalyzed asymmetric borylation.
The activation of ruthenium-indenylidene complexes containing two unsymmetrical unsaturated N-heterocyclic carbenes (u2-NHCs) by a transmetalation process is reported. The use of copper(I) or gold(I) chlorides promotes the rapid trapping of one NHC ligand that releases the catalytic active Ru-species. Impressive initiation rates with full-conversions are observed within one minute. This practical protocol demonstrates excellent catalytic performances in various ring-closing metathesis (RCM) and self-metathesis (SM).In a few decades, olefin metathesis has rapidly become one of the most efficient synthetic tools in organic chemistry This attractiveness was mainly due to the development of efficient, well-defined, air stable and easy to handle rutheniumarylidene complexes with high tolerance towards many organic functions. 1 Since the pioneer works describing the phosphine-based Grubbs first-generation catalyst in early 1990s, 2 the research efforts to furnish more robust and powerful complexes have drastically increased.
Naturally occurring isoquinolones
have gained considerable attention
over the years for their bioactive properties. While the late-stage
introduction of various functionalities at certain positions, namely,
C-3, C-4, and C-8, has been widely documented, the straightforward
introduction of challenging sp
3
carbon-linked acyclic aminoalkyl
or aza- and oxacyclic appendages at C-6 and C-7 remains largely underexplored.
Interest in 6-substituted azacyclic analogues has recently garnered
attention in connection with derivatives exhibiting anticancer activity.
Reported here is the first application of the versatile and recently
emerging field of Ni-catalyzed reductive cross-coupling reactions
to the synthesis of 6- and 7- hetero(cyclo)alkyl-substituted isoquinolones.
In a second and complementary approach, a new set of C-6- and C-7-substituted
positional isomers of hetero(cyclo)alkyl appendages were obtained
from the merging of photocatalytic and Ni-catalyzed coupling reactions.
In both cases, 6- and 7-bromo isoquinolones served as dual-purpose
reacting partners with readily available tosylates and carboxylic
acids, respectively.
A series
of new stereoretentive ruthenium catalysts bearing the
dithiocatecholate ligand was synthesiszed on the basis of the M7 and
Ru–benzylidene–oxazinone design. The activity of the
catalysts was tested in ring-opening cross-metathesis reactions, ring-closing
metathesis reactions, cross-metathesis reactions, and self-metathesis
reactions using Z- and E-configured
starting materials. The desired metathesis products were obtained
with moderate to high yields and with excellent stereoselectivities
(>95%). Substrate-dependent reactivity was found by carrying out
kinetic
studies on internal and terminal olefins.
SummaryA silver-free methodology was developed for the synthesis of unprecedented N-heterocyclic carbene ruthenium indenylidene complexes bearing a bidentate picolinate ligand. The highly stable (SIPr)(picolinate)RuCl(indenylidene) complex 4a (SIPr = 1,3-bis(2-6-diisopropylphenyl)imidazolidin-2-ylidene) demonstrated excellent latent behaviour in ring closing metathesis (RCM) reaction and could be activated in the presence of a Brønsted acid. The versatility of the catalyst 4a was subsequently demonstrated in RCM, cross-metathesis (CM) and enyne metathesis reactions.
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