Rhodium-Catalyzed Synthesis of Unsymmetric Di(heteroaryl)ureas Involving an Equilibrium Shift.

Unsymmetric di(heteroaryl)ureas such as HetAr1-NHCONH-HetAr2 are efficiently synthesized from two symmetric ureas, HetAr1-NHCONH-HetAr1 and HetAr2-NHCONH-HetAr2, by rhodium-catalyzed exchange reactions. The equilibrium in some of the reactions can be shifted to the formation of unsymmetric ureas by the aggregation of the dimers formed by inter- and intramolecular hydrogen bonding.

Dearomatization of 3-cyanoindoles by (3 + 2) cycloaddition: from batch to flow chemistry.

1,3-Dipolar dearomatizing cycloadditions between a non-stabilized azomethine ylide and 3-cyanoindoles or benzofuran afford the corresponding 3D-heterocycles bearing a quaternary carbon centre at the ring junction. While 6 equivalents of ylide precursor 1 are required for full conversion in a classical flask, working under flow conditions limits the excess (3 equiv., tR = 1 min) and leads to a cleaner process, affording cycloadducts that are easier to isolate.

Acid-catalyzed synthesis of condensed polycyclic diaryl ethers from arenols.

Diaryl ethers containing condensed polycyclic aryl groups were synthesized from arenols in the presence of a catalytic amount of p-chlorobenzenesulfonic acid. Symmetrical binaphthyl, biphenanthryl, and bipyrenyl ethers were obtained in high yields. Unsymmetrical derivatives were also synthesized from 9-phenanthrol and arenols, using combinations of reactive and unreactive substrates.

Catalytic Method for the Synthesis of C-N-Linked Bi(heteroaryl)s Using Heteroaryl Ethers and N-Benzoyl Heteroarenes.

C-N-linked bi(heteroaryl)s are synthesized by a rhodium-catalyzed N-heteroarylation reaction of N-benzoyl heteroarenes including azoles/azolones, pyridones, cyclic ureas, and cyclic imides using heteroaryl aryl ethers. The reaction involves the covalent bond-exchange reaction of N-CO and HetAr-O bonds without using metal bases and exhibits a broad applicability, giving diverse C-N-linked bi(heteroaryl)s containing five- and six-membered heteroarenes. The N-heteroarylation of N-H azoles/azolones and pyridone proceeds at higher reaction temperatures.

Rhodium-Catalyzed Synthesis of Unsymmetric Di(heteroaryl) Sulfides Using Heteroaryl Ethers and S-Heteroaryl Thioesters via Heteroarylthio Exchange.

Unsymmetric di(heteroaryl) sulfides were synthesized by a rhodium-catalyzed heteroarylthio exchange reaction of heteroaryl aryl ethers and S-(heteroaryl) thioesters. The reaction has broad applicability, giving diverse unsymmetric di(heteroaryl) sulfides containing five- and six-membered heteroarenes. No base is required in this reaction, which has been developed by the judicious design of organic substrates.

Rhodium-catalyzed P-P bond exchange reaction of diphosphine disulfides.

A rhodium-catalyzed exchange reaction of diphosphine disulfides, a diphosphine oxide, and a diphosphine is developed. Various symmetric diphosphine disulfides containing alkyl and phenyl groups are exchanged, giving equilibrium mixtures, from which unsymmetric diphosphine disulfides are readily separated by silica gel chromatography. The resulting unsymmetric diphosphine disulfide is regioselectively added to an aldehyde.

Rhodium-catalyzed transformation of heteroaryl aryl ethers into heteroaryl fluorides.

A rhodium complex catalyzed the conversion of the C-O bond of heteroaryl aryl ethers to the C-F bond. The reaction of (4-chlorophenylthio)pentafluorobenzene with heteroaryl aryl ethers provided heteroaryl fluorides and heteroaryl (4-chlorophenylthio)tetrafluorophenyl ethers; this involved the cleavage of a single heteroaryl C-O bond under equilibrium conditions. The reaction of heteroaryl aryl ethers with 2-fluorobenzothiazole in which two heteroaryl and aryl C-O bonds were cleaved provided heteroaryl fluorides and aryl fluorides. The reactions were applicable to five-membered and six-membered heteroaryl aryl ethers and also to diaryl ethers possessing one or two electron-withdrawing groups.

A palladium-catalyzed addition reaction of aroyl/heteroaroyl acid anhydrides to norbornenes.

A palladium complex derived from Pd2(dba)3 and dppp catalyzes the addition reaction of aroyl/heteroaroyl acid anhydrides to norbornenes, giving 2-aroyl/heteroaroyl-3-aroyloxy/heteroaroyloxy-bicyclo[2,2,1]heptanes. The C-O bond of acid anhydride is cleaved, and the aroyl/heteroaroyl and aroyloxy/heteroaroyloxy groups are added to alkenes. trans-Adducts are selectively obtained with the endo-benzoyl group and exo-benzoyloxy group.