Synthesis of arylboronates via Cp*RuCl-catalyzed cycloaddition of alkynylboronates

In the presence of 5-10 mol% Cp*RuCl(cod), 1,6- and 1,7-diynes were allowed to react with an ethynylboronate at ambient temperature to give rise to bicyclic arylboronates in 64-93% isolated yields. 1,6-Diynes bearing a boronate terminal also underwent cycloaddition with monoalkynes to give the corresponding bicyclic arylboronates.     

One-pot sequential four-component coupling via Cp*RuCl-catalyzed cyclotrimerization and Suzuki-Miyaura coupling

The catalytic intermolecular cyclotrimerization of alkynylboronates, propargyl alcohols, and terminal alkynes was accomplished by means of the ruthenium catalysis and the temporary tethering approach with the C-B-O linkage to give rise to highly substituted arylboronates with excellent selectivity. The resultant arylboronates were further converted to highly substituted biaryls via the Suzuki-Miyaura coupling with various aryl iodides using Pd₂(dba)₃/PCy₃ as a catalyst precursor in aqueous toluene. As a consequence, the four-component coupling approach to highly substituted biaryls was successfully established by combining these two operations into a sequential one-pot process.     

Synthesis of bi- and tricyclic arylboronates via Cp*RuCl-catalyzed cycloaddition of alpha,omega-diynes with ethynylboronate

In the presence of 5-10 mol% Cp*RuCl(cod), 1,6- and 1,7-diynes were allowed to react with an ethynylboronate at ambient temperature to give rise to bi- and tricyclic arylboronates in 64-93% isolated yields.     

Recent topics of Cp1RuCl-catalyzed annulation reactions

A wide variety of annulation reactions have been developed using Cp¹RuCl(cod) and related complexes as precatalysts. This digest highlights recent progress in Cp¹RuCl-catalyzed annulation reactions. State-of-the-art examples are outlined as follows: [2+2+2] cycloadditions, [2+2] cycloadditions, cyclizations of enynes, and other annulation reactions.     

Enantioselective synthesis of planar-chiral metacyclophanes through cationic Rh(I)/modified-BINAP-catalyzed inter- and intramolecular alkyne cyclotrimerizations

We have achieved the first catalytic enantioselective synthesis of planar-chiral metacyclophanes by means of cationic Rh(I)/(S)-xyl-H₈-BINAP or (R)-H₈-BINAP complex-catalyzed inter- and intramolecular alkyne cyclotrimerizations. This highly enantioselective catalysis represents a versatile new method for the preparation of planar-chiral metacyclophanes.     

Selective synthesis of anomeric α-glycosyl acetamides via intramolecular Staudinger ligation of the α-azides

α-Glycosyl azides can be transformed into the corresponding α-glycosyl acetamides with complete retention of configuration via reduction-acylation (Staudinger ligation) reactions using specifically functionalized phosphines. The α-acetamides of per-O-benzylated-fucose, per-O-benzylated-glucose and per-O-benzylated-galactose were selectively synthesized by this process.     

Selective synthesis of spiro[4,5]trienyl acetates via an intramolecular electrophilic ipso-iodocyclization process

A general and efficient intramolecular electrophilic ipso-iodocyclization of para-unactivated arylalkynes has been developed for the synthesis of spiro[4,5]trienyl acetates. In the presence of NIS (N-iodosuccimide) and HOAc, para-unactivated arylalkynes, including N-arylpropiolamides and phenyl 3-phenylpropiolate, underwent the intramolecular electrophilic ipso-iodocyclization smoothly in moderate to good yields.     

Pyridine synthesis from oximes and alkynes via rhodium(III) catalysis: Cp* and Cp(t) provide complementary selectivity

The synthesis of pyridines from readily available α,β-unsaturated oximes and alkynes under mild conditions and low temperatures using Rh(III) catalysis has been developed. It was found that the use of sterically different ligands allows for complementary selectivities to be achieved.     

Selective synthesis of clamshell-type bis-phthalocyanine bearing tetrachlorocyclotriphosphazene intramolecular bridge

The selective synthesis of clamshell-type bis-phthalocyanine was performed using cyclotriphosphazene as a peripheral spacer. The spectral characteristics of the target dye are similar to those of most H-dimers, and the reaction can be considered conditionally selective with respect to the cis-isomer     

Stereoselective gamma-lactam synthesis via palladium-catalysed intramolecular allylation

A novel route to the synthesis of 3-(tolylsulfonyl)-4,5-cis-disubstituted gamma-lactams using a diastereoselective palladium-catalysed intramolecular allylation of amino acid-derived allylic carbonates has been developed.     

Cp*RuCl-catalyzed [2 + 2 + 2] cycloadditions of alpha,omega-diynes with electron-deficient carbon-heteroatom multiple bonds leading to heterocycles

In the presence of a catalytic amount of Cp*RuCl(cod), 1,6-diynes were allowed to react chemo- and regioselectively with electron-deficient nitriles and heterocumulenes at 60-90 degrees C to afford heterocyclic compounds. The mechanism of the ruthenium-catalyzed regioselective formations of bicyclic pyridines and pyridones were analyzed on the basis of density functional calculations. Cyclocotrimerizations of ethyl propiolate with ethyl cyanoformate or propyl isocyanate gave rise to two of the four possible pyridine or pyridone regioisomers.     

Total synthesis of jimenezin via an intramolecular allylboration

[structure: see text] An efficient total synthesis of the annonaceous acetogenin jimenezin was achieved. The key steps used were a highly stereoselective intramolecular allylboration to establish the tetrahydropyran ring and an intramolecular Williamson reaction to close the tetrahydrofuran ring.     

Cp(*)RuCl-catalyzed formal intermolecular cyclotrimerization of three unsymmetrical alkynes through a boron temporary tether: regioselective four-component coupling synthesis of phthalides

Highly substituted phthalides were efficiently synthesized by sequential Cp(*)RuCl-catalyzed cyclotrimerization of alkynylboronates, propargyl alcohols, and terminal alkynes and palladium(II)-catalyzed carbonylation of the resultant arylboronates. The intermediate arylboronate was isolated and unambiguously characterized by X-ray crystallography. The perfect regioselectivity of the ruthenium-catalyzed formal intermolecular cyclotrimerization was discussed on the basis of the density functional calculations of a boraruthenacycle intermediate.     

Stepwise activation of "non-innocent" Cp* substituents--a Cp* based cascade reaction

Reactions of Cp* substituted pentelidene complexes with the primary phosphine Cp*PH(2) yield novel polycyclic phosphorus/arsenic and carbon containing cage compounds via cascade-like reactions. These reactions include a sequence of nucleophilic addition reactions, intramolecular hydrophosphination (partially hydroarsination) reactions, retro-Diels-Alder reactions with Cp*H elimination and subsequent [2+4]-cycloadditions.     

Enantioselective synthesis of P-stereogenic benzophospholanes via palladium-catalyzed intramolecular cyclization

Enantioselective or diastereoselective intramolecular cyclization of functionalized secondary phosphines or their borane adducts catalyzed by chiral Pd(diphosphine) complexes gave P-stereogenic benzophospholanes in up to 70% ee. These results provide a new method for the synthesis of chiral phospholanes, which are valuable ligands in asymmetric catalysis. [reaction: see text]     

Formal synthesis of salinosporamide A via NHC-catalyzed intramolecular lactonization

An N-heterocyclic carbene (NHC) catalyzed intramolecular lactonization to prepare densely functionalized bicyclic γ-lactam-γ-lactone adducts from enals is reported. This method has been applied to the formal synthesis of salinosporamide A, a potent 20S proteasome inhibitor and anti-cancer therapeutic.     

Iron-catalyzed synthesis of phenanthrenes via intramolecular hydroarylation of arene-alkynes

An Fe(OTf)₃-catalyzed intramolecular hydroarylation of arene-alkynes with high functional group tolerance has been reported, affording a series of phenanthrene derivatives efficiently. A low catalytic amount of Fe(OTf)₃ is applied in this reaction. This transformation provides a convenient and practical method for the preparation of phenanthrenes.     

Palladium-catalyzed synthesis of dibenzophosphole oxides via intramolecular dehydrogenative cyclization

Dibenzophosphole oxides were obtained from secondary hydrophosphine oxides with a biphenyl group by dehydrogenation via phosphine-hydrogen and carbon-hydrogen bond cleavage in the presence of a catalytic amount of palladium(II) acetate, Pd(OAc)(2). By using this reaction, a ladder-type dibenzophosphole oxide could also be synthesized by double intramolecular dehydrogenative cyclization.     

Facile synthesis of thiazoles via an intramolecular thia-Michael strategy

A mild and efficient method for the synthesis of substituted thiazoles is reported via one-pot N-desilylation, thioacylation/oxythioacylation/thiothioacylation followed by thia-Michael cycloisomerisation. This method has a general applicability to introduce various oxo and thio functionalities including aliphatic and aromatic moieties, especially at the C2-position of thiazoles.