Expedient Access to Polyaromatic Biaryls by Unconventional Ag-Catalyzed Cycloaromatization of Alkynylthiophenes and Au-Catalyzed Double C-H Activation.

An unconventional approach for the regioselective synthesis of polyaromatic biaryls via site-selective Ag-catalyzed twofold electrophilic cycloisomerization followed by Au-catalyzed double C-H activation is described. The developed process allows the synthesis of highly decorated biaryls with excellent regioselectivity. As revealed by DFT computations, the reaction represents a rare example of C1-C5 - and C1-C6 - cycloaromatization.

Ag(i)-Catalyzed cycloisomerization reactions: synthesis of substituted phenanthrenes and naphthothiophenes.

This paper describes silver catalyzed synthesis of substituted phenanthrenes and naphthothiophenes from ortho-alkylated biaryl derivatives via 6-endo-dig intramolecular alkyne-arene coupling. The mechanistic study reveals that 6-endo-dig cyclization proceeds through initial π-coordination of the alkyne unit followed by a Friedel-Crafts-type electrophilic aromatic cyclization at the adjacent arene ring. X-ray crystallographic studies further supported the formation of carbocycles.

Regioselective 5-endo-dig Electrophilic Iodocyclization of Enediynes: A Convenient Route to Iodo-substituted Indenes and Cyclopenta-Fused Arenes.

An efficient iodine-mediated regioselective tandem approach for the synthesis of symmetric and asymmetric iodo-substituted indenes and stereoselective cyclopenta [b]pyridine/thiophenes from easily accessible enediynes that proceeds by in situ formation of an iodonium intermediate followed by a regioselective 5-endo-dig cyclization has been described. The intramolecular electrophilic iodocyclization was selectively triggered by a distribution of electronic density along the alkyne bond. Subsequently, the iodo-substituted indenes were diversified by employing palladium-catalyzed cross-coupling reactions and the coupled products were further confirmed by X-ray crystallographic studies.

Pd-catalyzed one-pot sequential unsymmetrical cross-coupling reactions of aryl/heteroaryl 1,2-dihalides.

Efficient, step-economic, Pd(ii)-catalyzed one-pot sequential Sonogashira/Sonogashira, Sonogashira/Suzuki, Sonogashira/Heck, Suzuki/Sonogashira, Suzuki/Suzuki, Suzuki/Heck, Heck/Sonogashira, Heck/Suzuki and Heck/Heck cross coupling reactions of sterically hindered aryl/heteroaryl 1,2-dihalides have been developed. The present methodology allows the conversion of easily available aryl/heteroaryl 1,2-dihalides into synthetically useful unsymmetrically substituted arenes/heteroarenes in good to excellent yields under mild reaction conditions. This methodology is a powerful tool for building a versatile substrate which can be utilized for the synthesis of various organic scaffolds.

Pd(II)-Catalyzed C-H Activation of Styrylindoles: Short, Efficient, and Regioselective Synthesis of Functionalized Carbazoles.

A novel Pd(II)-catalyzed approach for the direct synthesis of highly functionalized carbazoles from unprotected styrylindoles has been developed. The reaction features a variety of olefin substrates, which are readily switchable by subtle tuning of the reaction conditions. Investigations of the mechanism suggest that the C-H activation proceeds via enamine formation.

Palladium-Catalyzed Triple Successive C-H Functionalization: Direct Synthesis of Functionalized Carbazoles from Indoles.

A novel Pd(II)-catalyzed approach for the direct synthesis of differentially substituted carbazoles from free (NH) indoles via regioselective triple successive oxidative Heck (Fujiwara-Moritani reaction) has been achieved. It is demonstrated that both electron-deficient and electron-rich alkenes could be used successively for the incorporation of two different functional groups into the product. The proposed mechanistic pathway was well supported by isolating the first and second successive oxidative Heck intermediates as well as by trapping with styrene-d3.

Pd-catalyzed Heck-conjoined amidation and concomitant chemoselective Michael-addition: an efficient tandem approach to highly functionalized tetrahydroquinazolines from o-haloanilines.

An efficient palladium-catalyzed tandem approach for the synthesis of highly functionalized tetrahydroquinazolines 4a–q, and 5a–f by the reaction of o-haloanilines 1a–g with acrylates 2a–d and isothiocyanates 3aa–3ah/isocyanates 3ba–3bfvia Heck-conjoined amidation/thioamidation and concomitant chemoselective Michael-addition is described. A competitive experiment showed that isothiocyanates were more reactive than isocyanates. The developed methodology offers an efficient chemoselective process for the synthesis of highly functionalized tetrahydroquinazolines under mild and operationally simple reaction conditions from inexpensive and commercially available starting substrates.