Iron-catalyzed intramolecular cyclotrimerization of triynes to annulated benzenes

Abstract

An iron species derived from FeCl 2 or FeCl 3 by in situ reduction with zinc powder in the presence of imidazol-2-ylidene or bidentate nitrogen ligand could effectively catalyze intramolecular cycloisomerization of triynes to annulated benzenes. With a 2-iminomethylpyridine ligand, hydrates of FeCl 2 and FeCl 3 as well as their anhydrous ones could be used.

Easy Entry into Reduced Ar‐BIANH2 Compounds: A New Class of Quinone/Hydroquinone‐Type Redox‐Active Couples with an Easily Tunable Potential

“…Compounds of the family bis(aryl)acenaphthenequinonediimine (Ar‐BIAN) ( 1 ; see Scheme ) have been known for some time,1–3 but have been brought to the general attention only in the 90s by Elsevier and his group 4. Since then, they have found widespread use mostly as ligands for transition metals and the corresponding complexes have been employed as catalysts for a wide variety of reactions, such as alkene hydrogenation,5 polymerization,6–11 copolymerization,12–18 aziridination,19 cyclopropanation,19 and epoxidation20 alkene‐CO copolymerization,21–24 alkyne coupling in the presence of halogens or organic halides and tin compounds25–27 or just tin compounds,28 selective semihydrogenation of alkynes29 and allenes,30 allylic aminations of olefins by nitroarenes in the presence of CO,31–33 the synthesis of pyrroles and oxazines from dienes, nitroarenes and CO,34 the reduction of nitroarenes to anilines by CO/H 2 O,35–37 the hydroamination of alkynes,38 the homo‐coupling of organic halides39 and their cross‐coupling reaction with organomagnesium, ‐zinc, and ‐tin reagents,40–44 the Suzuki–Miyaura cross coupling,45 the synthesis of 4‐quinolones and 2,3‐dihydroquinolones from 2′‐nitrochalcones and CO,46, 47 the synthesis of indoles from o ‐nitrostyrenes and CO,47, 48 the Heck arylation of olefins,49, 50 and oxidative Heck reaction,51, 52 the synthesis of dihydrofurans and dihydrobenzoxepines53 and N ‐acyl vinilogous carbamic acids,54 the cyclotrimerization of alkynes,55 the click reaction,56 the dimerization of vinyl ethers to acetals,57 and the diboration of α,β‐unsaturated carbonyl compounds 58. For some of these syntheses, the use of the Ar‐BIAN ligands was instrumental in achieving a high performance of the catalytic system.…”

Iron Catalysis in Synthetic Chemistry

“…Further, they showed the advantages of their method by efficient formation of carbocyclic, O-heterocyclic and biaryl compounds. In another report from the same group, N-based bidentate ligands (e.g., 1,2-diimines or 2-iminomethylpyridines) were utilized in ironcatalyzed chemo-and regioselective cyclotrimerization of triynes (16). Recently, Furstner et al (17) synthesized a fine blend of iron complexes of formal oxidation states 2, 0 and +1 from readily available ferrocene.…”

“…In 2002, Nguyen and co-workers (38) reported the olefin cyclopropanation using μ-oxo-bis[(salen)iron(III)] complexes [salen = N,N´-bis (3,5- (16)(17)(18)(19)(20) (Scheme 20). Thus, this (salen)iron complex (16) can be used as an efficient, selective, and inexpensive metal alternative to a widely used ruthenium(II) salen complex.…”

“…Thus, this (salen)iron complex (16) can be used as an efficient, selective, and inexpensive metal alternative to a widely used ruthenium(II) salen complex.…”

Synthesis, characterization, and applications of novel di-2-pyridyl imine ligands

“…Nitrogen ligands, such as amines [13], diazabutadienes [14], and salicylaldimines [15], have attracted considerable interest due to their stability and excellent activity. Unsymmetrical iminopyridine ligands containing one imino group and one pyridyl group have been extensively investigated and successfully employed recently in catalytic transformations including olefin polymerization and oligomerization [16][17][18][19][20], alkyne dimerization and cyclotrimerization [21][22][23][24], hydroboration and aromatic C-H borylation [25,26], hydrogenation of unsaturated hydrocarbons [27], and pyridine formation [28], and have been evaluated as potential anti-cancer agents [29]. In comparison, the chemistry of iminopyridine ligands containing two pyridyl groups is relatively unexplored [30][31][32].…”