Synthesis of chiral vinylic sulfoxides by Pd-catalyzed asymmetric sulfinylzincation

Novel asymmetric sulfinylzincation of alkynoates has been accomplished via a Pd-catalyzed sulfinylzincation using 1-alkynyl sulfoxides bearing chiral auxiliaries as a sulfinylating reagent. The reaction proceeded in a highly syn-selective fashion, giving the (E)-β-sulfinyl α,β-unsaturated ester exclusively. Among the chiral sulfinylating reagents tested, an isoborneol-type compound (Rs)-4 showed the best results in terms of both yield and diastereoselectivity. As a result of optimization of the reaction, the selectivity was improved up to 92:8 dr, and stereochemistry of the newly formed sulfur stereogenic center was revealed as (Ss)-configuration.     

Studies on hydrozirconation of 1-alkynyl sulfoxides or sulfones and the application for the synthesis of stereodefined vinyl sulfoxides or sulfones

The hydrozirconation reaction of 1-alkynyl sulfoxides or sulfones with Cp2Zr(H)Cl in THF at room temperature predominantly gave Z-beta-zirconated vinyl sulfoxides or sulfones with excellent regioselectivity. Compared with 1-alkynyl sulfoxides, the hydrozirconation reaction of 1-alkynyl sulfones exhibits great synthetic potential, leading to the efficient preparation of Z-beta-halovinyl sulfones, Z-beta-sulfonyl alpha,beta-unsaturated ketones, and Z-beta-alkynyl vinyl sulfones. Although the reaction mechanisms are still not clear, the neighboring group participation of the sulfinyl or sulfonyl group may be playing an important role in this unique hydrozirconation reaction.     

Geometrically selective synthesis of functionalized beta,beta-disubstituted vinylic sulfoxides by Cu-catalyzed conjugate addition of organozinc reagents to 1-alkynyl sulfoxides

[reaction: see text] A new synthetic method of chiral beta,beta-disubstituted vinylic sulfoxides bearing various functionalities has been developed by employing Cu-catalyzed conjugate addition of an organozinc reagent to chiral 1-alkynyl sulfoxide. Since the reaction proceeds with very high syn-selectivity, both geometric beta,beta-disubstituted vinylic sulfoxides were stereoselectively synthesized by changing the combination of 1-alkynyl sulfoxide and the organozinc reagent.     

Pd-catalyzed thiocarbamoylation of terminal alkynes with sulfenamide and carbon monoxide

Regio- and stereoselective thiocarbamoylation of terminal alkynes successfully took place using 2,4,5-tri-Cl-C₆H₂SNEt₂ as a reaction substrate and PdCl₂(PPh₃)₂/PPh₃/n-Bu₄NCl as a catalyst system.     

Pd-catalyzed reactions of o-diiodoarenes with alkynes for aromatic ring extension

[reaction: see text] A new and efficient palladium-catalyzed reaction of o-diiodoarenes with internal alkynes produces naphthalenes or anthracenes in good to excellent yields. This procedure provides a simple, catalytic, and straightforward ring-extension method for constructing substituted polycyclic aromatic compounds.     

Photoinversion of sulfoxides as a source of diversity in dynamic combinatorial chemistry

Photochemical interconversion of the two diastereoisomers cis- and trans-thianthrene dioxide (1) can be considered an example of photodynamic combinatorial chemistry (PDCC) in which the interconversion among diastereomeric equilibrating species is brought about by electromagnetic irradiation. Photoequilibrium can be shifted by irradiation at different wavelengths or by addition of SnCl(2) that binds cis-1 more efficiently than trans-1.     

Winding up alkynes: a Pd-catalyzed tandem-domino reaction to chiral biphenyls

Wrap it up! An intramolecular Pd-catalyzed tandem-domino process leading to highly sterically encumbered biphenyls is reported. The chirality of the newly formed axis is induced by the configuration of the carbohydrate backbone.     

Pd-catalyzed oxidative coupling of monosubstituted sydnones and terminal alkynes

The Pd-catalyzed oxidative coupling of N-substituted sydnones and terminal alkynes offers a quick, one-step synthesis of 4-alkynylsydnones in moderate to good yields.     

Regioselective Pd-catalyzed indolization of 2-bromoanilines with internal alkynes using phosphine-free ligands

The possibility of using phosphine-free ligands to promote Pd-catalyzed indolization of 2-bromoanilines with internal alkynes was examined for the first time. Phenylurea was found to be the optimal ligand, which could mediate the synthesis of 2,3-disubstituted indoles in good yields (ca. 60-85%) with high regioselectivity.     

BINOL derived C2-symmetric bis-sulfinates as efficient sulfinyl transfer agents in the synthesis of tert-butyl sulfoxides

The reaction of novel C₂-symmetric bis-sulfinate esters derived from (R)-BINOL with Grignard reagents affords tert-butyl sulfoxides in ee up to 97%. The desired enantiomer can be generated at will by the proper selection of BINOL.     

Synthesis of 3-substituted 4-aroylisoquinolines via Pd-catalyzed carbonylative cyclization of 2-(1-alkynyl)benzaldimines

A number of 3-substituted 4-aroylisoquinolines have been prepared in good yields by treating N-tert-butyl-2-(1-alkynyl)benzaldimines with aryl halides in the presence of CO and a palladium catalyst. Synthetically the methodology provides a simple and convenient route to isoquinolines containing an aryl, alkyl, or vinylic group at C-3 and an aroyl group at C-4 of the isoquinoline ring. The reaction is believed to proceed via cyclization of the alkyne containing a proximate nucleophilic center promoted by an acylpalladium complex.     

Synthesis of E-vinyl iodides via Pd-catalyzed hydrostannation of terminal alkynes

E-Vinyl iodides may be prepared via a one-pot reaction involving Pd-catalyzed hydrostannation of terminal alkynes followed by iodinolysis of the intermediate vinylstannane. The synthesis is tolerant of functional groups, such as alcohols and esters.     

Pd-catalyzed [2+2+1] coupling of alkynes and arenes: phenol diazonium salts as mechanistic trapdoors

Alkynes and phenol diazonium salts undergo a Pd-catalyzed [2+2+1] cyclization reaction to spiro[4,5]decatetraene-7-ones. This structure was confirmed for one example by X-ray single-crystal structure analysis. The reaction is believed to proceed through oxidative addition of the phenol diazonium cation to Pd(0), subsequent insertion of two alkynes, followed by irreversible spirocyclization.     

Cobalt-catalyzed reductive coupling of activated alkenes with alkynes

Cobalt complex/Zn systems effectively catalyze the reductive coupling of activated alkenes with alkynes in the presence of water to give substituted alkenes with very high regio- and stereoselectivity in excellent yields. While the intermolecular reaction of acrylates, acrylonitriles, and vinyl sulfones with alkynes takes place in the presence of CoI2(PPh3)2/Zn, the reaction of enones and enals with alkynes requires the use of the CoI2(dppe)/Zn/ZnI2 system. The intramolecular reductive coupling of activated alkenes (enones, enals, acrylates, and acrylonitriles) with alkynes also works efficiently. Further a variety of cyclic lactones and lactams were prepared using this methodology. Possible mechanistic pathways are proposed based on a deuterium-labeling experiment carried out in the presence of D2O.     

Pd-catalyzed reduction of aryl halides using dimethylformamide as the hydride source

The Pd-catalyzed homocoupling of aryl halides in a basic DMF solution is often accompanied by the dehalogenation of the substrate as side reaction. When an inorganic base such as sodium bicarbonate is used, the reducing role of the solvent has been demonstrated using DMF-d₇ and GC/MS analysis.     

Copper-catalyzed hydrostannation of activated alkynes

[reactions: see text] [(Ph3P)CuH]6 effectively catalyzes the hydrostannation of activated alkynes with exclusive regioselectivity for alpha-stannation. Syn hydrostannation is observed exclusively for alkynoates. Anti or syn hydrostannation adducts are obtained as products for alkynone substrates.     

Highly regiocontrolled Pd-catalyzed cross-coupling reaction of terminal alkynes and allenylphosphine oxides

The cross-coupling of a variety of terminal alkynes 1 with allenylphosphine oxides 2 catalyzed by a Pd(OAc)(2)-TDMPP system provided conjugated endo-enynes 3 solely, while the TCPC-catalyzed reaction of the same regents led to the exclusive formation of exo-isomers 4. The mechanistic rationale for these selective transformations was proposed. Synthetic usefulness of the prepared exo-enyne 4 was demonstrated in the synthesis of multisubstituted diarylbenzylphosphine oxides 5 via the Pd-catalyzed [4+2]-benzannulation reaction.