Copper-catalyzed intramolecular C-N bond formation: a straightforward synthesis of benzimidazole derivatives in water

A straightforward, efficient, and more sustainable copper-catalyzed method has been developed for intramolecular N-arylation providing the benzimidazole ring system. With Cu(2)O (5 mol %) as the catalyst, DMEDA (10 mol %) as the ligand, and K(2)CO(3) as the base, this protocol was applied to synthesize a small library of benzimidazoles in high yields. Remarkably, the reaction was exclusively carried out in water, rendering the methodology highly valuable from both environmental and economical points of view.     

Palladium-catalyzed intramolecular C-H activation/C-C bond formation: a straightforward synthesis of phenanthridines

The palladium-catalyzed intramolecular C-H activation/C-C cross-coupling has been developed for a straightforward and efficient synthesis of phenanthridines. With Pd(OAc)(2) (4 mol %) as the catalyst, PCy(3) (8 mol %) as the ligand, and Cs(2)CO(3) as the base, this protocol was applied to synthesize a small library of phenanthridine derivatives in good yields in THF.     

A reaction converting a w-w triple bond to a double bond: tetrakis-diethyldithiophosphate-disulfide-ditungsten,preparation and characterization

The reaction between W₂X₂(OR)₄ compounds [X = CH₂CMe₃ or OBu^t] and HS₂P(OEt)₂ (6 equivalents) in hydrocarbon solvents, produces a molecule of formula W₂S₂[S₂P(OEt)₂]₄ with corresponding elimination of alkane, alcohol and [(EtO)₂PS]₂. This tungsten compound has been characterized by IR,¹H,¹³C, and¹³P NMR spectroscopy, electronic absorption spectroscopy and single-crystal X-ray crystallography. The molecule adopts a structure based on an edge-shared bioctahedron, with two bridging sulfides, two chelating dithiophosphate ligands and two dithiophosphate ligands bridging the metal- metal double bond. The W-W distance of 2.5987(11)Åalong with the acute W—S—W angles of 67.74(8)dg, are consistent with the metalmetal double bond formulation Σ² π² . This structure is similar to the W₂S₂(S₂CNEt₂)₄ molecule prepared by Cotton et al. (Inorg. Chem. 1978,17, 2946).     

Bis-silicon-bridged stilbene homologues synthesized by new intramolecular reductive double cyclization

A homologous series of bis-silicon-bridged stilbenes has been synthesized on the basis of a new intramolecular reductive cyclization of bis(o-silyl)-diphenylacetylene. Thus, the reaction of bis(o-silyl)-diphenylacetylenes with excess lithium naphthalenide undergoes the two-electron reduction at the acetylene moiety to produce a dianion intermediate, which further undergoes a double cyclization in a 5-exo mode to produce the bis-silicon-bridged stilbenes. This methodology can also be applied to the synthesis of tetrakis-silicon-bridged bis(styryl)benzenes. The silicon-bridged pi-conjugated systems thus prepared show intense fluorescence in the visible region. Comparison of a bis-silicon-bridged stilbene with its carbon analogue demonstrates the substantial effects of the silicon-bridges on the electronic structures and thus on the fluorescence properties.     

Catalyzed intramolecular olefin insertion into a carbon-carbon single bond

Intramolecular insertion of a C-C double bond into a C-C single bond was achieved by treatment of cyclobutanone bearing an o-styryl group at the 3-position with a catalytic amount of a cationic rhodium(I)-dppp complex. Initially, rhodium is inserted between the carbonyl carbon and the alpha-carbon of the cyclobutanone. Intramolecular coordination of the vinyl group results in its migratory insertion into the C-Rh linkage. Reductive elimination affords benzobicyclo[3.2.1]octan-3-one. Notably, a ring-opened alpha,beta-unsaturated ketone was obtained when dppe was used instead of dppp. In this reaction, rhodium cleaved the bond between the alpha sp3 carbon and the beta sp3 carbon of the cyclobutanone. The coordinating vinyl group directs this new regioselectivity of cleavage observed with the dppe ligand.     

CN bond formation and cyclization: A straightforward and metal-free synthesis of N-1-alkyl-2-unsubstituted benzimidazoles

A straightforward and metal-free synthesis of N-1-alkyl-2-unsubstituted benzimidazoles from the corresponding o-fluoro aryl formamidines and primary amines using microwave irradiation is described. The displacement of -F by the primary amine and cyclization to form the corresponding benzimidazoles took place in one pot.     

A reversible pH-dependent intramolecular pyridine-aldehyde cyclization

A dipicolylamine (DPA) attached to an aldehyde moiety cyclizes to form a pyridinium-fused heterocycle. This intramolecular reaction between the pyridine and aldehyde moieties is reversible, and the position of the equilibrium is controlled by pH. The fused-ring heterocycle is stabilized under acidic conditions, whereas the ring-opened form is the major species under basic conditions. The ring-closed form can be utilized as a masked aldehyde precursor to access a variety of functional metal chelators containing the DPA unit.     

Intramolecular cyclization of phenol derivatives with CC double bond in a side chain

Intramolecular cyclization of phenol derivatives with CC double bond on a side chain was examined using copper and silver catalyst. For example, 2-allylphenol (1a) was converted to 2,3-dihydro-2-methylbenzofuran (2a) in 70% yield using Cu(OTf)₂ or in 90% yield using AgClO₄. This catalysis was applied to cyclization of 2-allylphenol derivatives, 2-(3-butenyl)phenol, benzoic acids with CC double bond, 2-allyl-N-tosylaniline, and 2-(3-butenyloxy)phenol. Furthermore, allyl phenyl ether was converted to 2a via Claisen rearrangement and cyclization.     

Copper-catalyzed cyclization of iodo-tryptophans: a straightforward synthesis of pyrroloindoles

Pyrroloindoles are a key structural motif found in a wide number of biologically active alkaloids. Intramolecular copper-catalyzed coupling of readily accessible 2-iodo-tryptophan derivatives occurs in excellent yield, affording a wide range of polysubstituted, enantioenriched tetrahydropyrrolo[2,3- b]indoles. Diketopiperazines are also suitable substrates for this cyclization reaction, which affords a straightforward entry to tetra- to hepta-polycyclic systems.     

A novel intramolecular Diels-Alder cyclization involving indoloazepines

The reaction of indoloazepines 1 and α,β-unsaturated aldehydes in reflux toluene led to tetracyclic compounds 2. The key to this reaction was an intramolecular Diels-Alder cycloaddition by the indoloacrylate (dienophile)-dienamine (diene) intermediates generated in situ.     

Palladium-catalyzed chloroimination of imidoyl chlorides to a triple bond: an intramolecular reaction leading to 4-chloroquinolines

In this paper, a new type of effective chloroimination was reported. This reaction afforded 4-chloro-2-perfluoroalkyl quinolines from fluorinated imidoyl chlorides in high yields. This is the first achievement of oxidative addition-reductive elimination type C-Cl bond activation by chloropalladation.     

Stereochemistry of protonation and mercuration of trisubstituted double bond during cyclization of isoprenoids

Conclusions Initiation of the reaction for the cyclization of isoprenoids by acids proceeds as a nonstereospecific process at the 2,3 bond, while when this reaction is initiated by mercury salts it proceeds as a stereospecific reaction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1151–1153, May, 1973.     

Stereospecific enzymic cyclization of a synthetic 2,3-oxidosqualene analogue bearing an 18Z carbon-carbon double bond

This report discloses the first successful cyclization of a squalene analogue bearing a Δ¹⁸ Z instead of E CC bond which leads to a lanosterol analogue possessing the unnatural 20S stereochemistry. The hypotheses of sterol biosynthesis are discussed in the light of these findings.     

A straightforward approach to N-substituted-2H-indazol-2-amines through reductive cyclization

A versatile two-step, one-pot reaction to access N-substituted-2H-indazol-2-amine derivatives has been elaborated. A diverse set of analogues was obtained by a sequential hydrazone formation and reductive cyclization in moderate to good yields from readily available starting materials. The strategy tolerates a broad range of substitutions pattern and functional groups allowing further derivatizations.     

Ruthenium-catalyzed intramolecular cyclization of hetero-functionalized allylbenzenes

Intramolecular addition of heterofunctionalities to CC double bonds without β-hydride elimination was investigated and catalyzed by ruthenium complexes. The combination of RuCl₃ · nH₂O (10 mol%) and 3 equiv. of AgOTf acted as a catalyst for cyclization of 2-allylphenol (1a) to 2,3-dihydro-2-methylbenzofuran (2a) in good yield in the presence of Cu(OTf)₂ as a co-catalyst and PPh₃ as a ligand. This catalyst system also catalyzed the cyclization of 2-allylbenzoic acid to lactone in 91% yield. Then, a new catalyst system (RuCp¹Cl₂)₂ (1.0 mol%)/4AgOTf/4PPh₃, was found to be more active even in the absence of Cu(OTf)₂. Furthermore, this catalysis was applied to asymmetric reaction of 2-allylphenol (1a). When using TolBINAP as a ligand, over 60% e.e. was achieved.     

Transition metal salts dependent intramolecular cyclization of a diimine

1,4-Bis(N-tosylethylamino)-2,3-diphenyl-1,4-diaza-1,3-butadiene (L¹) was separated from a condensation reaction of benzil with N-tosyl-ethylenediamine. It was shown that the intramolecular cyclization of L¹ has much dependence on the transition metal salts. The transformation of L¹ in the absence of any transition metal salts gave product 1-tosylaminoethyl-2-tosylaminomethyl-4,5-diphenyl-1H- imidazole (L²) at a temperature above 100 °C. Similar reactions assisted by Ni(CH₃COO)₂·4H₂O, MnCl₂·4H₂O, Mn(CH₃COO)₂·4H₂O, NiCl₂·6H₂O or NiSO₄·7H₂O could also give L² at a much lower temperature and a much higher yield. However, the presence of Cu(CH₃COO)₂·H₂O in a similar transformation reaction led to the formation of a bicyclic derivative 1-tosyl-5,6-diphenyl-1H-2,3-dihydroimidazo[1,2-a]imidazole (L³). But both L² and L³ were not detected when Co(CH₃COO)₂·4H₂O was used in a similar reaction and all attempts to transform L² into L³ failed.     

Self-consistent group calculations on polyatomic molecules V. Molecules with a double or triple bond

SCGF calculations are reported for the ground state of ethylene, formaldehyde, acetylene and hydrogen cyanide. A minimum basis of contracted Gaussians was used and optimum hybridization was determined for each of the molecules by systematic variation of the hybridization parameters until the total electronic energy was a minimum. Properties of CH bonds as well as CC, CO and CN σ and π bonds are discussed in some detail. The results show that the assumption of transferable framework integrals β, basic to all semiempirical methods of calculating molecular wave functions, is strictly justified within the SCGF method.     

Cytisine derivatives containing a triple bond

N-(-Acyloxy-2-butynyl)cytisines are obtained by the condensation of cytisine, via the Mannich reaction, with propargyl esters of monobasic carboxylic acids.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 655–656, May, 1971.