Palladium-catalyzed domino Heck/cyanation: synthesis of 3-cyanomethyloxindoles and their conversion to spirooxoindoles

3′-Alkyl-3-cyanomethyloxindoles, prepared by a palladium-catalyzed domino Heck/cyanation, were efficiently converted to spiropyrrolidinyl-, spiropiperidinyl- and spirocyclopropyl-oxindoles. The so-obtained spirooxindoles bearing three diversity points were further functionalized via selective N-acylation, N-alkylation, N-sulfonylation, S_NAr reaction and Buchwald-Hartwig N-arylation reaction to reach diverse set of heterocycles.     

Palladium-catalyzed enantioselective domino heck-cyanation sequence: development and application to the total synthesis of esermethole and physostigmine

An efficient synthesis of functionalized 3-alkyl-3-cyanomethyl-2-oxindole 1 by a palladium-catalyzed domino Heck-cyanation reaction has been developed. Reaction of ortho-iodoanilide 5 with potassium ferro(II)cyanide, K(4)[Fe(CN)(6)], dissolved in DMF in the presence of palladium acetate and sodium carbonate afforded oxindole 1 in good to excellent yields. An enantioselective domino Heck-cyanation process has been developed for the first time using (S)-DIFLUORPHOS as a chiral supporting ligand, and an enantioselectivity of up to 79 % ee in the enantiomerically enriched oxindole was obtained under optimized conditions. A concise total synthesis of esermethole and physostigmine, powerful inhibitors of acetyl- and butyryl-cholinesterase, is documented.     

The domino chemistry approach to molecular complexity: competing domino processes modulated by the substitution pattern

Oxidative cleavage with lead tetraacetate results in the synthesis of different oxygen heterocycles starting from the same unsaturated 1,2-diol of type I by tuning of the substitution pattern at the angular position. When this compound bears a functional substituent, such as an alkoxy, ester, alkenyl, or simply a hydrogen, more than one reaction pathway are in competition. The process allows for the selective formation of three different complex ring systems, by the appropriate choice of the angular substituent, leading to either a ring-expanded type 1, ring-retained type 2, or domino products 3.     

Palladium-catalyzed cyanomethylation of aryl halides through domino Suzuki coupling-isoxazole fragmentation

A one-pot protocol for the cyanomethylation of aryl halides through a palladium-catalyzed reaction with isoxazole-4-boronic acid pinacol ester was developed. Mechanistically, the reaction proceeds through (1) Suzuki coupling, (2) base-induced fragmentation, and (3) deformylation as shown by characterization of all postulated intermediates. Under optimized conditions (PdCl(2)dppf, KF, DMSO/H(2)O, 130 °C) a broad spectrum of aryl bromides could be converted into arylacetonitriles with up to 88% yield.     

Palladium-catalyzed atom transfer radical cyclization of unactivated alkyl iodide

A palladium-catalyzed atom transfer cyclization of unactivated alkyl iodide has been developed. A radical chain mechanism has been proposed for this transformation, which might not involve an alkylpalladium intermediate.     

Palladium-catalyzed domino protodecarboxylation/oxidative Heck reaction: regioselective arylation of coumarin-3-carboxylic acids

A protocol for straightforward and step-economical synthesis of neoflavones from coumarin-3-carboxylic acids is developed. This approach enables controlled protodecarboxylation/regioselective C–H arylation of coumain-3-carboxylic acids in one-pot using a monometallic catalytic system. A wide variety of electron-donating and -withdrawing substituents on both coumarins and arylboronic acid are tolerated under the reaction conditions and 4-aryl coumarins are constructed in high yields.     

An iodide/anion exchange route to benzimidazolylidene silver complexes from benzimidazolium iodide: Crystal structures of N,N′-dibutylbenzimidazolylidene silver chloride, bromide, cyanide and nitrate

Syntheses of N,N′-dibutylbenzimidazolylidene silver complexes having chloride, nitrate or cyanide as an anion part through an iodide/anion exchange from N,N′-dibutylbenzimidazolium iodide are described, representing a practical route to benzimidazolylidene silver complexes from readily accessible benzimidazolium iodide. The crystal structures of N,N′-dibutylbenzimidazolylidene silver chloride, bromide, cyanide and nitrate have been determined, showing a close ligand-unsupported Ag-Ag interaction in [(NHC)₂]Ag⁺[AgX₂]⁻ and a “T” shape geometry about the silver(I) cation in complexes of chloride, bromide and cyanide, but a nearly linear shape in the bis(N,N′-dibutylbenzimidazolylidene) silver complex [ with non-coordinating nitrate anion.     

Palladium-catalyzed cross-coupling reactions in one-pot multicatalytic processes

Palladium-catalyzed cross-coupling reactions have been investigated in multicatalytic processes to synthesize disubstituted alkenes and alkanes from carbonyl derivatives. The use of copper-catalyzed methylenation reactions is the key starting reaction to produce terminal alkenes which are not isolated, but submitted to further structure elongation. Not only is the isolation of the alkene intermediate unnecessary, but also the copper catalyst is a beneficial cocatalyst in the palladium-catalyzed cross-coupling reactions. The desired products are thus typically obtained in higher yields using this one-pot approach. We have used these processes to synthesize hydroxylated (E)-stilbenoids, which are known chemopreventive and chemotherapeutic agents, odorant-substituted indanes, and non-natural amino acids, such as homophenylalanine.     

Palladium-catalyzed domino ring-opening/carboxamidation reactions of N-tosyl aziridines and 2-iodothiophenols: a facile and efficient approach to 1,4-benzothiazepin-5-ones

A novel and efficient domino procedure has been developed for the synthesis of 1,4-benzothiazepin-5-ones from simple and readily accessible N-tosyl aziridines and o-iodothiophenols. This process involves aziridines ring-opening with o-iodothiophenols, followed by palladium-catalyzed intramolecular carboxamidation. The scope and limitation of this transformation have been investigated in detail by using various aziridines and o-iodothiophenols.     

Determination of nitrite and mixtures of bromide and iodide with o-iodosobenzoate

Nitrite diazotizes sulphanilamide, which then does not undergo 3,5-dibromination. Nitrite can therefore be determined by reaction with excess of sulphanilamide, the surplus of which is then titrated with o-iodosobenzoate or chloramine-T in the presence of potassium bromide, with Methyl Red as indicator. Mixtures of iodide and bromide can be analysed by oxidation of the iodide with excess of o-iodosobenzoate at pH 4-6, followed by extraction of the iodine (which is then titrated with thiosulphate) and then oxidation of the bromide in dilute sulphuric acid medium in the presence of sulphanilamide as bromine scavenger, the residual oxidant being evaluated iodometrically.     

The enthalpimetric determination of mixtures of chloride,bromide and iodide

The individual components of mixtures of chloride (0–1 mmol), bromide and iodide (0–0.1 mmol) may be determined by the use of direct injection enthalpimetry. The heats of reaction of the ions with various reagents have been shown to be additive and the use of non-selective reagents is thus made possible. The amounts of the halides present are calculated by simultaneous equations. The limits of the methods are discussed.