Insertion of polar and nonpolar unsaturated molecules into carbon-rhenium bonds generated by C-H bond activation: synthesis of phthalimidine and indene derivatives

A rhenium complex, [ReBr(CO)(3)(thf)](2), catalyzes the reaction of an aromatic aldimine with an isocyanate and an acetylene to give a phthalimidine and an indene derivative in a quantitative yield, respectively. The reactions proceed via C-H bond activation, insertion of the isocyanate or the acetylene, intramolecular nucleophilic cyclization to the aldimine of the generated amido- or alkenyl-rhenium species, and reductive elimination. In contrast to ruthenium and rhodium catalysts, which are usually employed in this type of reaction, the rhenium catalyst promotes the insertion of a polar unsaturated molecule. This occurs more easily than the insertion of a nonpolar unsaturated molecule.     

Synthesis of Cp-Re complexes via olefinic C-H activation and successive formation of cyclopentadienes

Treatment of an alpha,beta-unsaturated ketimine with an alpha,beta-unsaturated carbonyl compound in the presence of a rhenium complex, Re2(CO)10, gave a cyclopentadienyl-rhenium complex. This reaction proceeds via rhenium-catalyzed C-H bond activation of an olefinic C-H bond, insertion of an alpha,beta-unsaturated carbonyl compound into a Re-C bond of the alkenylrhenium intermediate, intramolecular nucleophilic cyclization, reductive elimination, elimination of aniline to give a cyclopentadiene derivative, followed by the formation of a cyclopentadienyl-rhenium complex from the cyclopentadiene derivative and the rhenium complex.     

Rhenium-catalyzed synthesis of naphthalene derivatives via insertion of aldehydes into a C-H bond

A rhenium complex, [ReBr(CO)₃(THF)]₂, catalyzed reactions of aromatic ketimines and aldehydes with dienophiles, followed by dehydration, to give naphthalene derivatives in good to excellent yields. This reaction proceeds via C-H bond activation, insertion of an aldehyde, intramolecular nucleophilic cyclization, reductive elimination, elimination of aniline and Diels-Alder reaction. After dehydration, naphthalene derivatives were formed.     

Mutual Cooperation in the Formal Allyl Alcohol Nucleophilic Substitution and Hydration of Alkynes for the Construction of γ‐Substituted Ketones

Mutual cooperation in the formal allyl alcohol nucleophilic substitution reaction and hydration of an alkyne has been utilized in the presence of a gold catalyst to give a series of γ‐functionalized ketones with high to excellent yields. This reaction actually involved an intramolecular O?H insertion cyclization of an alkyne to form the dihydrofuran intermediate, which was followed by the nucleophilic addition ring‐opening of a dihydrofuran to give the target compound.     

Rhenium-catalyzed regioselective synthesis of multisubstituted pyridines from β-enamino ketones and alkynes via C-C bond cleavage

A new method is described for the regioselective synthesis of multisubstituted pyridine derivatives. Treatment of N-acetyl β-enamino ketones with alkynes in the presence of the rhenium catalyst, Re(2)(CO)(10), gives multisubstituted pyridines regioselectively. In this reaction, the N-acetyl moieties are important for the selective formation of the multisubstituted pyridines. This reaction proceeds via insertion of alkynes into a carbon-carbon single bond of β-enamino ketones, intramolecular nucleophilic cyclization, and elimination of acetic acid.     

Synthesis of indolequinones via a Sonogashira coupling/cyclization cascade reaction

A mild strategy for constructing indolequinone motifs is described on the basis of the Sonogashira reaction and a copper-catalyzed intramolecular cyclization cascade reaction. The first step involves the palladium- and copper-catalyzed reaction between halogenated naphthoquinone and terminal acetylene to generate a coupling product, which then reacts in a copper-catalyzed intramolecular cyclization with the nitrogen functional group adjacent to the carbon-carbon triple bond.     

Efficient catalytic insertion of acetylenes into a carbon-carbon single bond of nonstrained cyclic compounds under mild conditions

A rhenium complex, [ReBr(CO)3(thf)]2, catalyzes the reaction of a 1,3-dicarbonyl cyclic compound with an acetylene to give a medium-sized cyclic compound in excellent yield. By using isocyanide as an additive, the catalytic activity of the rhenium complex changes dramatically, and the insertion of acetylenes into a carbon-carbon single bond occurs under mild conditions. A plausible mechanism is that the reaction proceeds via the formation of a rhenacyclopentene intermediate, ring opening by a retro-aldol reaction, isomerization, and reductive elimination.     

Ruthenium (II)-catalyzed synthesis of phthalides via the cascade addition and cyclization of aromatic acids with aldehydes

The ruthenium-catalyzed intermolecular cascade cyclization of aromatic acids with aromatic aldehydes, which involves the direct insertion of C–H bond into a polar C=O bond and the successive intramolecular nucleophilic substitution, was developed for the synthesis of 3-substituted phthalides in good to excellent yields. This one-pot procedure characterizes in a short reaction time, the cheaper Ru(II) as a catalyst, readily available acids and aldehydes as starting materials, and water as the only theoretical by-product.These merits make the protocol an efficient and cost-effective route for the synthesis of 3-substituted phthalides.     

N-heterocyclic carbene catalyzed nucleophilic substitution reaction for construction of benzopyrones and benzofuranones

N-Heterocyclic carbene as an efficient organic catalyst was employed to catalyze an intramolecular nucleophilic substitution reaction. When R(2) was a phenyl group, the cyclization process underwent isomerization, leading to generation of benzofuranone.     

An unusual Me3SiI-promoted [4+2] annulation and reduction: an efficient approach to construct 4H-benzopyrans

Me(3)SiI-promoted reaction of salicylic aldehydes with β-dicarbonyl compounds provided a facile way to construct 4H-benzopyrans in moderate to good yields. This tandem reaction proceeds with high efficiency through nucleophilic addition, silyl enol ether formation, substitution, reduction, and intramolecular nucleophilic cyclization.     

Palladium(0)-catalyzed cyclization of 1,6-diyn-3-yl carbonates with a nucleophilic functionality: efficient synthesis of polycyclic benzo[b]fluorene derivatives via allene intermediates

We report in this paper an interesting tandem reaction involving sequential palladium(0)-catalyzed decarboxylation of diynylic carbonates, intramolecular nucleophilic cyclization and Schmittel reaction, which provides a facile method for the synthesis of a variety of polycyclic benzo[b]fluorene derivatives from easily accessible starting materials.     

Reversal of nucleophilicity of enamides in water: control of cyclization pathways by reaction media for the orthogonal synthesis of dihydropyridinone and pyrrolidinone Clausena alkaloids

A highly efficient, metal-free, and divergent method for the synthesis of 3,4-dihydropyridin-2-one and pyrrolidin-2-one Clausena alkaloids and their analogs is reported. While the oxirane-containing enamides underwent the TFA-mediated 6-endo-enamide-epoxide cyclization reaction in Bu(t)OH to produce homoclausenamides, an unprecedented nucleophilic reaction occurred at the alpha-carbon of enamides in water to yield 5-endo-enamide-epoxide cyclization products in excellent yields. The reversal of nucleophilicity of enamides in intramolecular cyclization is discussed in terms of steric and electronic effects of the oxirane-containing enamides.     

Convenient synthetic route to a dehydrorotenoid via selective intramolecular aldol condensation of 1,2-diaryl diketone

Synthesis of dehydrorotenoid (1) was successfully achieved via an intramolecular aldol reaction of the corresponding 1,2-diaryl diketone intermediate. The 1,2-diaryl diketone was prepared using a ruthenium-catalyzed oxidation of the corresponding substituted diaryl acetylene. Treatment of this 1,2-diketone with l-proline induced a selective intramolecular aldol condensation reaction, forming the desired benzopyranone over the alternative benzofuran. Deprotection, cyclization, and dehydration gave the target compound in good overall yield.     

A regiospecific synthesis of 1-methylamino-6-fluoro-7-(4-methylpiperazin-1-yl)-1,4-dihydro-4-oxoquinoline-3-carboxylic acid

An efficient and regiospecific synthesis of 1-methylamino-6-fluoro-7-(4-methylpiperizin-1-yl)-1,4-dihydro-4-oxoquinoline-3-carboxylic acid ( 3 ) via an intramolecular nucleophilic displacement cyclization reaction is reported.     

Synthesis of cyclic alkenyl ethers via intramolecular cyclization of O-alkynylbenzaldehydes. Importance of combination between CuI catalyst and DMF

An efficient and remarkably general method for the synthesis of cyclic alkenyl ethers via the Cu(I)-catalyzed intramolecular cyclization of O-alkynylbenzaldehydes has been developed. The survey of metal catalysts and solvents revealed that the combination of copper(I) iodide and DMF was the catalytic system of choice. The reaction most probably proceeds via the nucleophilic addition of alcohols 2 to O-alkynylbenzaldehydes 1 to generate the corresponding hemiacetals, and subsequent nucleophilic attack of the hemiacetal oxygen to the copper coordinated alkyne would give the annulation products 3. In all cases, the reaction proceeded in a regiospecific manner leading to the six-membered endocyclic products via 6-endo-dig cyclization.     

General silaindene synthesis based on intramolecular reductive cyclization toward new fluorescent silicon-containing pi-electron materials

[reaction: see text] The reaction of (o-silylphenyl)acetylene derivatives with lithium naphthalenide undergoes intramolecular reductive cyclization to produce various silaindene derivatives. On the basis of this methodology, a series of silaindene-containing pi-electron systems are synthesized that show intense blue to greenish-blue fluorescence.     

Nucleophilic addition to electron-rich heteroaromatics: dearomatizing anionic cyclizations of pyrrolecarboxamides

[reaction: see text] Despite its electron-rich nature, a pyrrole ring is susceptible to intramolecular nucleophilic attack by organolithiums. The resulting dearomatizing anionic cyclization yields new 5- or 7-membered heterocyclic rings. Formation of a new 5-membered ring, by cyclization of an N-benzylpyrrolecarboxamide, is accompanied by ring opening of the original pyrrole to yield 3-aminovinylpyrrolinones. Formation of a new 7-membered ring, by cyclization of an N-allyl pyrrolecarboxamide, yields bicyclic pyrroloazepinones.     

One Pot Spiropyrazoline Synthesis via Intramolecular Cyclization/Methylation

Regioisomeric spiropyrazolines were synthesized through a tandem intramolecular cyclization/methylation reaction of a functionalized 5,5-disubstituted pyrazoline in one reaction vessel. The 5,5-pyrazolines were constructed through a 1,3-dipolar cycloaddition reaction of aromatic ring containing nitrile imines and a disubstituted geminal alkene. An evaluation of the relative location of the nucleophilic and electrophilic functional groups on the pyrazoline was performed in order to ascertain the best pyrazoline system for the intramolecular cyclization/methylation reaction. Higher spiropyrazoline isolated yields were realized from pyrazolines with the electrophilic ester located further away from the pyrazoline when compared to pyrazolines with a directly bonded ester.     

Synthesis of highly functionalized oxazines by Vilsmeier cyclization of amidoalkyl naphthols

The intramolecular cyclization of amidoalkyl naphthols by Vilsmeier reagent produced 1,3-oxazines. The Vilsmeier reagent (chloromethylenedimethylammonium chloride) has been used as an efficient and cheap acid activator for the one-step synthesis of oxazine derivatives. A mechanism involving sequential haloformylation and intramolecular nucleophilic cyclization is proposed.     

Synthesis of xanthones, thioxanthones, and acridones by the coupling of arynes and substituted benzoates

The reaction of silylaryl triflates, CsF, and ortho-heteroatom-substituted benzoates affords a general and efficient way to prepare biologically interesting xanthones, thioxanthones, and acridones. This chemistry presumably proceeds by a tandem intermolecular nucleophilic coupling of the benzoate with an aryne and a subsequent intramolecular electrophilic cyclization.