A Combined Experimental and Computational Study on the Cycloisomerization of 2‐Ethynylbiaryls Catalyzed by Dicationic Arene Ruthenium Complexes
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Abstract Ruthenium‐catalyzed cycloisomerization of 2‐ethynylbiaryls was investigated to identify an optimal ruthenium catalyst system. A combination of [η 6 ‐( p ‐cymene)RuCl 2 (PR 3 )] and two equivalents of AgPF 6 effectively converted 2‐ethynylbiphenyls into phenanthrenes in chlorobenzene at 120 °C over 20 h. Moreover, 2‐ethynylheterobiaryls were found to be favorable substrates for this ruthenium catalysis, thus achieving the cycloisomerization of previously unused heterocyclic substrates. Moreover, several control experiments and DFT calculations of model complexes were performed to propose a plausible reaction mechanism.Keywords:
Cycloisomerization
Phenanthrenes
Chlorobenzene
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Abstract A novel gold‐catalyzed 6‐ exo ‐ dig cycloisomerization of o ‐propargylbiaryls has been developed that provides ready access to functionalized phenanthrenes in largely good to excellent yields. Notable features of this method are readily available starting materials, mild reaction conditions, and broad substrate scope.
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Phenanthrenes
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Readily available o'-alkenyl-o-alkynylbiaryls, a particular type of 1,7-enynes, undergo a selective cycloisomerization reaction in the presence of a gold(I) catalyst to give interesting phenanthrene and dihydrophenanthrene derivatives in high yields. The solvent used provokes a switch in the evolution of the gold intermediate and plays a key role in the reaction outcome.
Cycloisomerization
Phenanthrenes
Biphenyl
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Abstract Various functionalized phenanthrenes are synthesized with good functional group tolerance by a general and practical method starting from readily available o‐propargyl biaryls under mild reaction conditions.
Phenanthrenes
Cycloisomerization
Propargyl
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Cycloisomerization
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Abstract Ruthenium‐catalyzed cycloisomerization of 2‐ethynylbiaryls was investigated to identify an optimal ruthenium catalyst system. A combination of [η 6 ‐( p ‐cymene)RuCl 2 (PR 3 )] and two equivalents of AgPF 6 effectively converted 2‐ethynylbiphenyls into phenanthrenes in chlorobenzene at 120 °C over 20 h. Moreover, 2‐ethynylheterobiaryls were found to be favorable substrates for this ruthenium catalysis, thus achieving the cycloisomerization of previously unused heterocyclic substrates. Moreover, several control experiments and DFT calculations of model complexes were performed to propose a plausible reaction mechanism.
Cycloisomerization
Phenanthrenes
Chlorobenzene
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Abstract Ortho‐alkynyl biaryls react in the presence of catalytic amount of Brønsted acids to give phenanthrenes in high yields under mild conditions. The activity and selectivity of this transformation are governed by the substitution pattern of the diarylalkyne moiety. Selectivity shifts are observed between the carbophilic Lewis and Brønsted acid‐catalyzed cycloisomerization involving alkyne activation. magnified image
Cycloisomerization
Phenanthrenes
Moiety
Brønsted–Lowry acid–base theory
Alkyne
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Abstract A new PtCl 2 /PtCl 4 ‐catalyzed hydroarylation/cycloisomerization cascade reaction leading to the formation of two aromatic or heteroaromatic rings in one step is reported. The strategy developed is exemplified by the synthesis of the 5,6‐dihydrobenzo[ c ]phenanthrene and 6 H ‐naphtho[2,1‐ c ]chromene skeletons. Attempts to prepare [8]helicene‐like molecules are also discussed.
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Helicene
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In our efforts to probe the reaction mechanism of the endo cycloisomerization of alkynols catalyzed by the complex [Ru(N3P)(OAc)](BPh4) (1; NP3 = N,N-bis[(pyridin-2-yl)methyl][2-(diphenylphosphino)phenyl]methanamine), the reactions of 1 with alkynes were investigated. Several complexes related to intermediates in the catalytic reactions were isolated and characterized. In the presence of DIPEA (N,N-diisopropylethanamine), complex 1 reacted with 3-butyn-1-ol to afford the Ru−oxocyclocarbene complex {Ru(N3P)[═C(CH2)3O](OAc)}(BPh4) (4). Under anhydrous conditions, the reaction of complex 1 with tert-butylacetylene afforded [Ru(N3P)(η3-tBuC≡CC═CHBut)](BPh4) (8). In the presence of water, the reaction of complex 1 with tert-butylacetylene afforded [Ru(N3P)(CO)(η1-CH2But)](BPh4) (13). All the reactions are likely to proceed through ruthenium vinylidene intermediates. These results support that ruthenium vinylidene complexes are involved as the key intermediates in the cycloisomerization of alkynols catalyzed by complex 1.
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Abstract Numerous functionalized phenanthrenes are obtained via In(III)‐catalyzed electrophile‐promoted nucleophilic cyclization of o‐propargylbiaryls.Various functionalized groups are tolerated on the alkynyl carbon.
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Cycloisomerization
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