Solvent-Switchable Remote C-H Activation via 1,4-Palladium Migration Enables Site-Selective C-P Bond Formation: A Tool for the Synthesis of -Chiral Phosphinyl Imidazoles.

Solvent-switchable and site-selective phosphorylation of imidazoles at the C2 or C5 position of the imidazole ring was achieved via 1,4-palladium migration. -Chiral -butyl(aryl)phosphine oxides were cross-coupled to 1-(2-bromophenyl)-1-imidazoles with high enantiospecificity, thereby leading to a novel class of chiral imidazole-based phosphine oxides. As proof of concept, reduction of an analogue yielded the corresponding -chiral 2-phosphinyl imidazole ligand, which was shown to induce high enantioselectivity in the formation of axially chiral molecules synthesized via Pd-catalyzed Suzuki-Miyaura cross-coupling.

Rhodium-catalyzed Sommelet-Hauser type rearrangement of α-diazoimines: synthesis of functionalized enamides.

An efficient rhodium catalyzed Sommelet-Hauser type rearrangement of sulfur ylides derived from α-thioesters and N-sulfonyl-1,2,3-triazoles has been successfully accomplished for the synthesis of various functionalized enamides. The developed reaction involves the unprecedented [2,3]-sigmatropic rearrangement of sulfur ylides with the imine motif. Importantly, the method works well with various substituted α-thioesters/-amides/-ketones and substituted N-sulfonyl-1,2,3-triazoles and allows the synthesis of diverse enamide derivatives in good to excellent yields.

Rhodium-Catalyzed Rearrangement of S/Se-Ylides for the Synthesis of Substituted Vinylogous Carbonates.

An efficient rhodium-catalyzed unprecedented oxa-[2,3]-sigmatropic rearrangement of sulfur ylide derived from α-thioesters/ketones and diazo carbonyl compounds has been accomplished for the synthesis of various sulfur-tethered vinylogous carbonates in good to excellent yields. Important features of the developed reaction include wide functional group tolerance, excellent chemo- and regioselectivity, and efficient rearrangement involving the carbonyl motif. The present reaction also equally works well with α-selenoesters for the synthesis of seleno-containing vinylogous carbonates.

Rhodium Catalyzed Synthesis of Benzopyrans via Transannulation of N-Sulfonyl-1,2,3-triazoles with 2-Hydroxybenzyl Alcohols.

An efficient and novel rhodium-catalyzed transannulation of N-sulfonyl-1,2,3-triazoles with in situ generated o-quinone methides ( o-QMs) from 2-hydroxybenzyl alcohols has been achieved for the synthesis of substituted benzopyrans in good yields. The developed reaction involves nucleophilic attack of o-QM to α-imino rhodium carbenoid to generate a carbonyl ylide followed by 6π-electrocyclization and isomerization. Furthermore, the utility of the methodology was demonstrated in the one-pot synthesis and construction of polyheteroaromatics.

Divergent Functionalization of N-Alkyl-2-alkenylanilines: Efficient Synthesis of Substituted Indoles and Quinolines.

An efficient divergent functionalization of N-alkylated ortho-alkenylanilines to substituted indoles and quinolines has been accomplished by employing rhodium-catalyzed cross-dehydrogenative coupling and silver-mediated oxidative cyclization, respectively. The developed methods tolerate various functional groups and allow the synthesis of substituted indoles and quinolines in good to excellent yield. Synthetic utility is demonstrated through conversion to an indole with antimicrobial activity and C-H bond functionalization of 2-arylquinolines.

Cobalt(III)-Catalyzed Intramolecular Cross-Dehydrogenative C-H/X-H Coupling: Efficient Synthesis of Indoles and Benzofurans.

An efficient cobalt(III)-catalyzed intramolecular cross-dehydrogenative C-H/N-H coupling of ortho-alkenylanilines has been developed utilizing O as a terminal oxidant. The developed reaction tolerates various reactive functional groups and allows the synthesis of diverse indole derivatives in good to excellent yields. The method was successfully extended to the synthesis of benzofurans through the intramolecular cross-dehydrogenative C-H/O-H coupling of ortho-alkenylphenols.

Rhodium catalyzed diastereoselective synthesis of 2,2,3,3-tetrasubstituted indolines from -sulfonyl-1,2,3-triazoles and -vinylanilines.

An efficient diastereoselective rhodium catalyzed synthesis of indolines possessing two contiguous tetrasubstituted carbon centers has been achieved with good to excellent yields using -vinylanilines and iminocarbenes derived from -sulfonyl-1,2,3-triazoles. The reaction affords excellent -diastereoselectivity through the initial formation of a -ylide followed by intramolecular trapping with unactivated alkenes an ene-type reaction with a well-organized transition state, namely intramolecular carbenylative amination of alkenes. The developed transformation was further extended to the successful synthesis of tricyclic compounds, imidazoindolines, through reduction and hypervalent iodine mediated oxidative cyclization.