Phosphorylthioacetamides in the synthesis of annulated quinoxalines

Diethoxyphosphorylthioacetamide in the reaction with 2,3-dichloroquinoxaline acted as a thionating reagent, giving diethoxyphosphorylacetonitrile and 2-chloro-3-[(3-chloro-2-quinoxalinyl)thio]quinoxaline. Reactions of phosphorylthioacetamides with N-methylquinoxalinium iodide in alcohol media in the presence of a base proceeded stereoselectively to afford cis-3-phosphoryl-1,3,3a,4,9,9a-hexahydro-2H-pyrrolo[2,3-b]quinoxaline-2-thiones. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1010–1013, May, 2007.     

The six-membered annulation reaction involving sequential palladium-catalyzed allylic alkylation and Michael addition: scope and limitations

The palladium-catalyzed condensation of a variety of active methylene compounds with methyl 6-acetoxymethyl-hepta-2,6-dienoate was investigated. The six-membered adducts resulting from a η³ palladium complex alkylation-Michael addition sequence were obtained with moderate to good yields. In some cases, further evolution of the primary adduct was observed. The process has been expanded to access nitrogen heterocycles by using sodium p-toluenesulfonamide as the nucleophilic partner.     

Synthesis of new 4-(1-ethylthio-2,2,2-trifluoroethyl)-6-methylpyridazin-3(2H)-ones starting from S-ethyl 4-oxo-2-(pentafluoroethyl)pentanethiolate and hydrazines

The paper presents a one-pot conversion of γ-keto-α-pentafluoroethyl thioester into new pyridazin-3-ones and α,β-unsaturated lactams. The structures of all new compounds were ascribed using 1D (¹⁹F, ¹H, ¹³C) and 2D (¹H-¹⁵N) NMR data, and X-ray diffraction analysis. Two possible competitive reaction mechanisms for the synthesis of pyridazin-3-ones and lactams are presented.     

From solution-phase to solid-phase enyne metathesis: crossover in the relative performance of two commonly used ruthenium pre-catalysts

A crossover in the ability of two distinct ruthenium-based metathesis pre-catalysts to effect the synthesis of dialkenylboronic esters in solution and on the solid-phase was observed. Specifically, while the Grubbs 2nd generation pre-catalyst 3 affords a greater degree of conversion to product than the Hoveyda-Grubbs pre-catalyst 2 in a solution-phase enyne-metathesis reaction, this trend is reversed in the solid-phase variant. Systematic investigation showed this trend to be general, regardless of variations in the homoallylic alcohol and alkynylboronic ester components of the reaction, as well as in the type of solid support employed. Experiments to determine a mechanistic hypothesis for this trend highlighted the significance of the ruthenium remaining bound to the substrate after metathetic rearrangement and found the presence of phosphine ligand to be detrimental to the success of the solid-phase reaction. Therefore, these results suggest an expanded role for phosphine-free pre-catalysts, such as 2, in challenging solid-phase metathesis reactions.     

Furan ring opening-furan ring closure: cascade rearrangement of novel 4-acetoxy-9-furylnaphtho[2,3-b]furans

The cascade rearrangement of novel 4-acetoxy-9-furylnaphtho[2,3-b]furans leading to tetracyclic naphthodifurans derivatives has been developed. The reaction proceeds via double recyclization of both furan rings of the initial molecule, one of the furan rings serving as a 1,3-dicarbonyl compound equivalent.     

Synthesis of 2,5-bis{(diethyl-3′-indolyl)methyl}furan and its N,N′-dimetallated complexes (lithium, sodium and potassium): X-ray crystal structures of 2,5-bis{(diethyl-3′-indolyl)methyl}furan and the polymeric tetrahydrofuran adduct of the dilithiated complex

The synthesis of 2,5-bis{(diethyl-3′-indolyl)methyl}furan by the acid catalysed condensation of 2,5-bis(diethylhydroxymethyl)furan with indole is presented. Dilithium, disodium and dipotassium derivatives are prepared by the reaction of the bis(indole) with n-BuLi, NaH and K, respectively, in the presence of various Lewis bases. The X-ray structures of 2,5-bis{(diethyl-3′-indolyl)methyl}furan and the dilithiated derivative (as a polymeric tetrahydrofuran adduct) are reported.     

Simple route to 3-(2-indolyl)-1-propanones via a furan recyclization reaction

A simple route to 1-R-3-(2-indolyl)-1-propanones has been elaborated based on recyclization of 2-(2-aminobenzyl)furan derivatives. Being a modification of the Reissert indole synthesis, our approach employs the furan ring as a source of carbonyl function. This approach is general and allows varying of substituents in aromatic ring as well as in 3-position of indole nucleus.     

Synthesis and some transformations of new 9-furylnaphtho[2,3-b]furan derivatives

The synthesis of a number of naphtho[2,3-b]furan derivatives, containing a furyl substituent in position 9 by intramolecular cyclization of 2-carboxy and 2-formylbis(5-alkylfur-2-yl)methanes is described. The reactivity of the title compounds in formylation, acetylation, nitration, and oxidation reactions has been investigated. It was shown that nitration of 2-methyl-9-(5-methyl-2-furyl)naphtho[2,3-b]furan-4-yl acetate leads to oxidative furan ring opening rather than to electrophilic substitution.     

Transition Metal-Catalyzed Intermolecular Cascade C−H Activation/Annulation Processes for the Synthesis of Polycycles

Polycycles are abundantly present in numerous advanced chemicals, functional materials, bioactive molecules and natural products. However, the strategies for the synthesis of polycycles are limited to classical reactions and transition metal-catalyzed cross-coupling reactions, requiring pre-functionalized starting materials and lengthy synthetic operations. The emergence of novel approaches shows great promise for the fields of organic/medicinal/materials chemistry. Among them, transition metal-catalyzed C−H activation followed by intermolecular annulation reactions prevail, due to their straightforward manner with high atom- and step-economy, providing rapid, concise and efficient methods for the construction of diverse polycycles. Several strategies have been developed for the synthesis of polycycles, relying on sequential multiple C−H activation/annulation, or combination of C−H activation/annulation and further interaction with a proximal group, or merger of C−H activation with a cycloaddition reaction, or in situ formation of the directing group. These are attractive, efficient, step- and atom-economic methods starting from commercially available materials. This Minireview will provide an introduction to transition metal-catalyzed C−H activation for the synthesis of polycycles, helping researchers to discover indirect connections and reveal hidden opportunities. It will also promote the discovery of novel synthetic strategies relying on C−H activation.