Indium triflate mediated tandem acetalisation-acetal exchange reactions under solvent-free conditions

Acyclic acetals and ketals undergo exchange reactions in the presence of catalytic quantities of indium(III) triflate and diols to generate the corresponding cyclic acetals and ketals in excellent yield. The protocol is rapid, employs mild conditions and can be adapted to employ solvent-free reaction conditions. We have further developed this methodology to encompass a tandem acetalisation-acetal exchange protocol which provides facile access to cyclic ketals from unreactive ketones also under very mild, solvent-free reaction conditions.     

One-pot synthesis of dihydropyrimidiones catalyzed by strontium(II) triflate under solvent-free conditions

A simple, efficient and practical procedure for the Biginelli reaction using strontium(II) triflate [Sr(OTf)₂] as a novel catalyst is described under solvent-free conditions in high yields. The catalyst exhibited remarkable reactivity and it is reusable. Some of dihydropyrimidiones showed strong pesticidal activity.     

Indium(III) catalysed substrate selective hydrothiolation of terminal alkynes

In(OTf)(3) is reported as the first catalyst having the ability to selectively catalyse both Markovnikov and anti-Markovnikov hydrothiolation of terminal alkynes under identical reaction conditions depending upon the nature of the thiol employed.     

Efficient trans-acetoacylation mediated by ytterbium(III) triflate as a catalyst under solvent-free condition

A simple and efficient trans-acetoacylation method for the synthesis of β-keto ester derivatives has been described using ytterbium(III) triflate as a new catalyst under solvent-free condition. This method was found to be efficient and convenient for the synthesis of a wide variety of β-keto ester derivatives.     

Indium(III)-catalysed aryl sulfonylation reactions

A rapid, high yielding and regioselective process has been developed for the synthesis of biaryl sulfones via sulfonylation reactions catalysed by indium(III) chloride.     

Unprecedented Barbier-type reactions catalysed by titanocene(III)

Selective Barbier-type allylations, benzylations and propargylations of aldehydes and ketones can be carried out under extremely mild conditions employing titanocene(III) complexes as catalysts. In this way, chiral titanocene catalysts provided yields ranging from 50-80% of optically active products.     

Ytterbium triflate catalysed Meerwein-Ponndorf-Verley (MPV) reduction

Ytterbium triflate was shown to be effective in promoting the reduction of substituted aromatic and aliphatic aldehydes and ketones using isopropanol as the solvent and the reducing agent. The whole process furnished the desired adducts in 22-98% yield.     

Synthetic and structural comparisons of bismuth(III) carboxylates synthesised under solvent-free and reflux conditions

Two synthetic approaches to the formation of bismuth(III) carboxylates have been explored and compared. Ph(3)Bi was reacted with a series of carboxylic acids (RCO(2)H) of varying pK(a) and functionality (R = PhCH[double bond, length as m-dash]CH, o-MeOC(6)H(4), m-MeOC(6)H(4), o-H(2)NC(6)H, o-O(2)NC(6)H(4), p-O(2)NC(6)H(4), 2-(C(5)H(4)N)) under reflux conditions in toluene and solvent-free. The thermochemical profiles of the solvent-free reactions were also studied by DSC-TGA. All reactions produced the tri-substituted bismuth carboxylates in comparable yields and purity with the exceptions of picolinic acid and p-nitrobenzoic acid. 2-Picolinic acid exclusively formed the di-substituted complex, [PhBi(2-(C(5)H(4)N)CO(2))(2)](4), by both methods, while p-nitrobenzoic acid gave the tri-substituted complex through reflux and the di-substituted complex under solvent-free conditions. Two of the complexes were structurally authenticated by single crystal X-ray diffraction: [PhBi(2-(C(5)H(4)N)CO(2))(2)](4) is tetrameric formed through five membered chelate rings involving the pyridyl N and O(-C) rather than the less stable carboxylate (-CO(2)) chelates, while [Bi(o-MeOC(6)H(4)CO(2))(3)](infinity), is a polymer in which dimeric units, constructed around two chelating and one unsymmetrical bridging carboxylate on each Bi centre, are then joined together through longer intermolecular Bi-O bridging bonds.     

Enantioselective glyoxylate-ene reactions catalysed by (salen)chromium(III) complexes

An enantioselective carbonyl-ene reaction of alkyl glyoxylates with various 1,1-disubstituted olefins, catalysed by chiral (salen)Cr(III)BF₄ complexes, has been studied. We found that a chromium complex bearing adamantyl substituents at the 3,3′-positions of the salicylidene moiety catalysed the reaction with much greater selectively than the classic Jacobsen-type catalyst. The reaction proceeded effectively under undemanding conditions in the presence of 2 mol % of the catalyst in an acceptable yield and with 59-92% ee.     

Efficient functionalization of aromatic C-H bonds catalyzed by gold(III) under mild and solvent-free conditions

A gold(III)-catalyzed carbon-carbon bond formation reaction between arenes and electron-deficient alkynes or alkenes is described. Electron-rich arenes can be efficiently functionalized with the alkyne or alkene substrates. This reaction can be run with neat reactants at ambient temperature. Under the "solventless" conditions, clean product was obtained from a reaction of equal molar amounts of arene and alkyne substrates. The mild conditions and potential tolerance to different functional groups make this method practical for arene functionalization and for constructing complicated molecules. Efficient preparation of various coumarins from aryl alkynoates was demonstrated. Preliminary mechanistic studies were performed to probe the pathway of this reaction.     

Mechanistic insight into the lanthanide(III) salt catalysed monoacylation of symmetrical diols from structural models

Model studies are presented that suggest the mechanism of the lanthanide(III) salt catalysed mono acylation of symmetrical diols proceeds via chelation of the diol and the anhydride to the lanthanide salt, followed by an 'intramolecular' acyl transfer.     

Synthesis of 1,1-diacetates catalysed by silica-supported boron sulfonic acid under solvent-free conditions and ambient temperature

1,1-Diacetates derivatives were prepared using the direct condensation of aldehydes with acetic anhydride in the presence of silica-supported boron sulfonic acid (SiO₂/B(SO₄H)₃) as a tri-functional inorganic Brønsted acid catalyst under solvent-free conditions at ambient temperature. The salient features of this methodology are: (i) cheaper process ready availability of the catalyst; (ii) versatility; (iii) high regio-selectivity of the procedure and recyclable property of the catalyst.     

Cyanuric chloride catalysed rapid conversion of ��-ketoesters into ��-enaminoesters under mild and solvent-free conditions

Cyanuric chloride is shown to be an extremely efficient catalyst for the synthesis of ??-enaminoesters from ??-ketoesters under solvent-free conditions by grinding in a mortar with pestle at 25 °C. A short reaction time, an inexpensive and easily available catalyst, mild reaction conditions and excellent yields of the products are attractive features of this methodology.     

Oxidation of steroidal diols and triols with air/NaH

Abstract  

The unusual air oxidation of steroidal triols and diols in the presence of sodium hydride in THF is described. The initial oxidation product, ketone or aldehyde, frequently undergoes further transformations in the reaction medium. The course of the reaction depends on the stereochemistry of the substrate. For example, oxidation of (20R)-20-hydroxymethyl-6β-methoxy-3α,5α-cyclopregnane-16β,17α-diol with air/NaH afforded 6β-methoxy-23,24,25,26,27-pentanor-3α,5α-cyclofurostane-16α,17α-diol in 60% yield whereas similar reaction of (20R)-20-hydroxymethyl-6β-methoxy-3α,5α-cyclopregnane-16α,17α-diol gave 6β-methoxy-D-homo-16a-oxa-3α,5α-cycloandrostan-16-one in 30% yield. The objective of this preliminary study was to select alcohols susceptible to air/NaH oxidation and to establish the effect of conditions on the course of the reaction.     

Synthesis of bis(indolyl)methanes under catalyst-free and solvent-free conditions

Abstract

Condensation of indole with aromatic aldehydes has been carried out without using any catalyst and solvent to give bis(indolyl)methanes.     

Highly efficient three-component (aldehyde-alkyne-amine) coupling reactions catalyzed by a reusable PS-supported NHC-Ag(I) under solvent-free reaction conditions

The development of a highly efficient, polystyrene-supported NHC-Ag(I) catalyst for the three-component coupling reactions of aldehydes, alkynes, and amines (A³-coupling) was described. In the presence of PS-NHC-Ag(I) (2 mol %), the A³-reactions were carried out at room temperature under solvent-free reaction conditions and the corresponding propargylamines were generated in good to excellent yields. Furthermore, the catalyst could be reused at least 12 times without a significant loss of its catalytic activity.     

Mercaptokomplexe von Indium(III)

The complexes of In(III) with thioglycolate (HO? CH₂? CH₂? S^?) have been investigated by pH-metric methods. Only the mononuclear species In(SR)_n(3-n)+ (n = 1, 2, 3, 4) are formed (Fig. 1): It was difficult to obtain an accurate value for the first stability constant K₁ because of the high stability of the 1:1-complex and therefore mixtures of KCl-KNO₃ were used to keep up the ionic strength of μ = 0.1. In presence of chloride, the constants K_n are smaller because of the formation of chloro complexes and mixed complexes In(SR)_nCl_i(3-n-1)+ and the stability constants of these have also been determined. The constants for the complexes without coordinated chloride can finally be obtained by an extrapolation (Fig. 2). The problem of the influence of increasing charge on the stability of various complexes of the isoelectronic 4d¹⁰ cations is discussed (Fig. 3).     

Indium(III) coordination compounds

Data on the homo- and heteroleptic coordination compounds of indium(III) with halide, pseudo-halide, and N,O-donor ligands are generalized. Trends in the coordination numbers and coordination polyhedron geometries and the specifics of formation of hybrid polymer structures are considered. 182 references.