Search

The reaction of biphenylene with various nitriles in the presence of catalytic amount of [Rh(cod)2BF4]/dppe under microwave irradiation afforded 9-substituted phenanthridines. The reaction with alkyl and aromatic nitriles provided the corresponding 9-substituted phenanthridines in 26–79% isolated yields. The reaction was also carried out with cyanopyridines and it provided heterocyclic compounds with the bipyridine and terpyridine scaffold. The synthesized bipyridine and terpyridine were complexed with [Rh(cod)Cl]2. The former provided a Rh(III) complex in which the cyclooctadiene moiety was oxidized to the tetrahydrofuran ring, whereas the latter gave a structurally fluxional complex (in solution) with only one pyridine ring coordinated to the rhodium atom.

The enantioselective allylation of an aromatic aldehyde to give a chiral homoallylic alcohol was employed as the key step in the syntheses of a flobufen metabolite and dapoxetine. In the former case, the homoallylic alcohol moiety (99 % ee) was converted into a five-membered lactone ring with good preservation of the optical purity, and the target compound, a flobufen metabolite, was obtained in 95 % ee. In the latter case, the homoallylic alcohol moiety (97 % ee) was transformed over several steps into a 3-aminopropanol moiety. During the course of the synthesis, the gradual loss of optical purity was observed, and the target compound, dapoxetine, was obtained in 85 % ee.

Substituted phenanthrenes and picenes were easily prepared by reaction of biphenylene or angular [3]phenylene with various alkynes in the presence of a catalytic amount of [IrCl(cod)](2) /dppe (cod=1,5-cyclooctadiene, dppe=1,2-bis(diphenylphosphino)ethane). The reaction is based on C-C bond activation of the cyclobutane ring. The reaction tolerates the presence of bulky groups on the alkyne, such as the ferrocene moiety. In addition, a catalytic system based on [RhCl(cod)](2)/dppe enabled the, hitherto unreported, reaction of biphenylene with nitriles to provide phenanthridines.

Dibutyl zirconocene-mediated TRANS-selectivecyclization of methoxyallyl-ene followed by the reaction with electrophiles isa convenient method for the synthesis of functionalized cyclopentanederivatives. Ring-closing metathesis of the obtained cyclopentanederivative yielded a common building block for the synthesis ofsesquiterpene analogues with unnatural TRANS-[3.4.0]bicyclo-nonaneskeleton.

The enantioselective allylation of aldehydes (I) and (VIII) with pinacolborane (II) in the presence of a chiral BINOL-phosphoric-acid-derived catalyst is the key step in the synthesis of the flubofen metabolite (VII) and dapoxetine (X).

Chiral iron compounds have been overlooked as potential catalysts in organic synthesis. However, advances in this area within the last decade have revealed only a small part of their potential. There is no doubt that in the near future this field will flourish and further expand to deliver useful processes that will enrich the pool of synthetic methodologies. The aim of this review is to summarize advances in development of enantioselective iron-complex catalyzed processes and their application in organic synthesis. These processes include oxidative coupling reactions electron-rich arenes, cycloaddition reactions of unsaturated compounds (e.g. Diels-Alder reaction, [3+2] and [4-4] cycloadditions), aldol reactions of silylated enol ethers, carbometallations of cycloalkenes, thia- and oxa-conjugated additions, Friedel-Crafts reaction, opening of small ring compounds (epoxides), oxidations (epoxidation, dihydroxylation, heteroatom oxidation, and kinetic resolution), reductions (carbonyl group reduction), and other processes (aziridination, carbene insertions). Keywords: iron catalysis; enantioselective catalysis; coupling reaction; cycloaddition reaction; aldol reaction; carbometallation; conjugated addition; Friedel-Crafts reaction; oxidation; reduction; carbenes

Biphenylene (I) or angular [3]phenylene (IV) undergo an iridium-catalyzed reaction with various internal alkynes to give substituted phenanthrenes and picenes, correspondingly.