Lewis Acid-catalyzed Reactions Research Articles

ChemInform Abstract: Lewis Acid-Catalyzed Reactions of α,β-Unsaturated N,N- Dimethylhydrazones with 1,4-Benzoquinone. Formation of Indoles by a Novel Oxidative Rearrangement.

ChemInform Abstract: Lewis Acid-Catalyzed Reactions of α,β-Unsaturated N,N- Dimethylhydrazones with 1,4-Benzoquinone. Formation of Indoles by a Novel Oxidative Rearrangement.

ChemInform Abstract: Lewis Acid-Catalyzed Ene Reactions of Esters of 2- Trifluoromethylpropenoic Acid.

ChemInform Abstract: Lewis Acid-Catalyzed Ene Reactions of Esters of 2- Trifluoromethylpropenoic Acid.

ChemInform Abstract: Lewis-Acid-Induced Reaction of Silicon-Containing Stannyl Ketones and Its Application to the Synthesis of (+)-β-Cuparenone.

Abstract (+)-β-Cuparenone was synthesized by the Lewis-acid catalyzed reaction of a β-stannylcyclohexanone derivative.

Exceptional molecular architectures via cycloadditions to pyrenequinones

The thermal reaction of phencyclone (2) with a 1:1 mixture of 1,8-pyrenequinone (4) and 1,6-pyrenequinone (5) yields 2:1 adducts only of compounds 2 and 4. The observed polycyclic aromatic hydrocarbon 8 is formed via double Diels–Alder addition of 2 to 4, and the polycyclic ketone 9 arises from a combination of Diels–Alder and hetero-Diels–Alder reactions of 2 and 4. In contrast, Lewis acid-catalyzed reactions of 2, 4, and 5 give 2:1 adducts only of 2 and 5. The chief product, polycyclic diketone 10, is derived from a double hetero-Diels–Alder addition of 2 to 5. X-ray analysis of compound 8 shows it to be an exceptionally large polycyclic aromatic arch, and the X-ray structure of 10 reveals it to be a chiral molecular tweezer.

Lewis acid catalyzed rapid synthesis of 5-hydroxy-benzo[ g]indole scaffolds by a modified Nenitzescu reaction

A fast solvent-less synthesis of 5-hydroxy-benzo[ g]indole scaffolds is accomplished from Lewis acid-catalyzed one-pot reaction of naphthoquinone, ω-morpholinoacetophenone, and urea under microwave irradiation. The key step in the synthesis is the Michael addition followed by in situ aza cyclization reaction using urea as an environmentally benign source of ammonia.

ChemInform Abstract: Synthesis and Fluoride-Promoted Wittig Rearrangements of α-Alkoxysilanes.

Lewis acid-catalyzed reaction of allyl and benzyl trichloroacetimidates with α-silyl alcohols was found to be a general method for the synthesis of α-alkoxysilanes. Upon exposure to CsF, these α-alkoxysilanes could be made to undergo [2,3]-Wittig rearrangement with an efficiency similar to that realized by the analogous but inherently more toxic α-alkoxystannanes.

ChemInform Abstract: New Efficient Method for the Stereoselective Synthesis of α-(Trifluoromethyl)-α,β-unsaturated Amides. Lewis Acid-Catalyzed Reaction of 3,3,3-Trifluoro-1-propynylamine with Carbonyl Compounds.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Lewis Acid-Catalyzed Hydrometalation and Carbometalation of Unactivated Alkynes

Hydrosilylation, hydrostannation, carbosilylation, and carbostannation of unactivated alkynes with organosilanes, or organostannanes proceed effectively in the presence of catalytic amounts of Lewis acids to produce the corresponding vinylsilyl or vinylstannyl compounds in a highly regio- and stereoselective way. Although it is well known that transition metal catalyzed hydrometalations and carbometalations, in general, proceed in a cis-manner, the Lewis acid-catalyzed reactions proceed in a trans-manner exclusively. The coordination of a triple bond to Lewis acids is proposed as a key step for the Lewis acid catalyzed reactions.

Intramolecular substitution reactions involving π-nucleophiles and N-acyliminium cations generated from azetidin-2-ones

The Lewis acid-catalyzed intramolecular substitution reactions of 4-vinyloxy- or 4-acyloxy-azetidin-2-ones with nitrogen-bound allyl-, propargyl- and vinyl-silanes leading to the carbacephams or carbacephems, are reported. The formation of carbapenams was not observed. To illustrate the potential of these reactions to be carried out under solid-phase conditions, a synthesis of diastereomeric 5-vinyl-carbacephams via the cyclization/cleavage methodology was performed.

Lewis acid-catalyzed one-pot sequential reaction for the synthesis of α-halogenated β-keto esters

Abstract A Lewis acid-catalyzed one-pot sequential transformation of β-keto esters, aromatic aldehydes, and NCS/NBS was reported. The reaction proceeds by way of Knoevenagel condensation/Nazarov cyclization/halogenation to give α-chloro- and α-bromo-β-keto esters in moderate yields with high diastereoselectivities. However, several aromatic aldehydes with electron-withdrawing substituents afforded unexpected α,β′-dichloro-β-keto esters in good to high yields.

Soy-based UV-curable thiol–ene coatings

Novel soy-based thiols and enes were synthesized and characterized. Then, soy-based thiol–ene UV-curable coatings were formulated and their coating physiochemical properties were investigated in detail. The use of biorenewable resources, combined with environmentally friendly UV-curable technology, provides a “green + green” solution to the stricter regulations in the coatings industry. Novel soy-based thiols and enes were synthesized through the Lewis acid-catalyzed ring opening reaction of epoxidized soybean oil with multifunctional thiols or hydroxyl functional allyl compounds. FTIR and NMR confirmed the formation of the target compounds. The soy-based thiols and enes were formulated with petrochemical-based enes and thiols, respectively, to make thiol–ene UV-curable coatings. Typical coating film properties, thermal properties, and photopolymerization kinetics of these coatings were studied. Soy-based thiol–ene coatings having lower functionality thiols and enes have poor UV curability and coating properties, which was attributed to the lower crosslink density. Soy-based thiols and enes with higher functionality can be UV-cured in combination with petrochemical-based enes or thiols even without the presence of free radical photoinitiators. Better coating film properties were obtained from these higher functionality thiol–ene systems that were toughened by commercial hyperbranched acrylates.

Highly diastereoselective Friedel–Crafts reaction of indoles with an N-tert-butanesulfinylimino ester: an efficient and practical approach to enantiomerically enriched α-(3-indolyl)glycines

An efficient, mild and general method for the preparation of highly enantiomerically enriched alpha-(3-indolyl)glycines by the transition-metal-based Lewis acid-catalyzed diastereoselective Friedel-Crafts reaction of indoles with an N-tert-butanesulfinylimino ester has been developed.

Facile Synthesis of 2,6-Disubstituted Benzobisthiazoles: Functional Monomers for the Design of Organic Semiconductors

The synthesis of several synthetically useful 2,6-disubstituted benzobisthiazoles is described. The method is based on the Lewis acid-catalyzed ring-closing reaction between substituted orthoesters and diamino benzene dithiol. The resulting benzobisthiazoles are obtained cleanly and in good yields. These materials are of interest for the development of new organic semiconductors.

Steroselective synthesis of some steroidal oxazolines, as novel potential inhibitors of 17α-hydroxylase-C 17,20-lyase

17β-Oxazolinyl steroids 7a– g and 8a– g were synthesized. The Lewis acid-catalysed reactions of (20 R)-3β-acetoxy-21-azidomethyl-20-hydroxypregn-5-ene with substituted aromatic aldehydes led to the formation of 3β-acetoxyandrost-5-enes substituted in position 17β with oxazolinyl residues ( 7a– g). Oppenauer oxidation of the 3β-hydroxy- exo-heterocyclic steroids yielded the corresponding Δ 4-3-ketosteroids. The inhibitory effects (IC 50) of both 3-hydroxy compounds 7a– g and their Δ 4-3-keto counterparts 8a– g on rat testicular C 17,20-lyase were investigated with an in vitro radioligand incubation technique. The 3-chlorophenyl- ( 8d), and the 4-bromophenyl-17β-(2-oxazolin-5-yl)androst-4-en-3-one derivatives ( 8f) were found to be modest inhibitors (IC 50 = 4.8 and 5.0 μM, respectively).

Synthesis and Structure of an Extremely Air‐Stable Binuclear Hafnocene Perfluorooctanesulfonate Complex and Its Use in Lewis Acid‐Catalyzed Reactions

Stable complexes: An extremely air-stable mu(2)-hydroxy-bridged binuclear hafonocene perfluorooctanesulfoante complex shows high catalytic efficiency in Lewis acid-catalyzed reactions, such as esterification, Friedel-Crafts acylation, the Mukaiyama aldol reation, and the allylation of aldehyde (see scheme).An extremely air-stable mu(2)-hydroxy-bridged binuclear hafonocene perfluorooctanesulfoante complex was successfully synthesized. This complex showed high catalytic efficiency in the esterification of alcohols, phenol, thiol, and amines, in the Friedel-Crafts acylation of alylaryl ethers, in the Mukaiyama aldol reaction, and in the allylation of aldehydes and could be reused.

Lewis acid-catalyzed reactions of N′-(2-alkynylbenzylidene)hydrazides with diethyl phosphite

Lewis acid catalyst-tuned reactions of N′-(2-alkynylbenzylidene)hydrazides with diethyl phosphite are described. Isoquinolin-1-ylphosphonate is generated when copper triflate is utilized as catalyst, while 2-amino-1,2-dihydroisoquinolin-1-ylphosphonate is obtained in the presence of palladium acetate.

Lewis acid-catalyzed reactions of donor–acceptor cyclopropanes with furan derivatives

Lewis acid-catalyzed reactions of dialkyl 2-arylcyclopropane-1,1-dicarboxylates with 2,5-dimethylfuran were found to give products of [3+2]-cycloaddition to C(2)–C(3) bond, which contain reactive vinyl ether moiety. These adducts can be further transformed into various products depending on the Lewis acid, the nucleophilicity of aryl group in starting cyclopropane and the ratio of reagents. The vinyl ether moiety can attack the appropriate nucleophilic center in intramolecular or intermolecular mode or can undergo cycloaddition to the second equivalent of donor–acceptor cyclopropane. Alternatively, 2,5-diphenylfuran formed Friedel–Crafts products only when reacted with donor–acceptor cyclopropanes.

Shuttling Germanium Atoms into Branched Polysilanes

Lewis acid-catalyzed rearrangement reactions of trimethylgermylated small permethylated oligosilanes were found to show a strong tendency of the germanium atoms to move to the more highly silylated positions of the molecule. This makes possible the construction of molecules with high germanium content in the core parts of the molecules by the following repeated sequence: introduction of trimethylgermyl group followed by rearrangement. Quantum-mechanical computations at the B3LYP/6-311+G(d,p) level suggest that the exergonic rearrangement proceeds in a reaction cascade via germylium and silylium ions, which transform by 1,2-silyl and -methyl shifts.

Synthetic studies toward the pyran core and the amide side chain of psymberin

A synthetic approach to the polysubstituted pyran core and amide side chain of psymberin (irciniastatin A) using stereoselective organoboron methodology is described. An advanced oxyranyl pyran intermediate was prepared using a catalytic enantioselective and diastereoselective three-component reaction involving first an inverse electron-demand hetero [4+2] cycloaddition between 3-boronoacrolein pinacolate and 1-ethoxy-2-methylpropene, followed by an allylboration of ethyl glyoxylate. The amide side chain was prepared highly efficiently using the first example of a doubly diastereoselective allylboration of a chiral α-alkoxy aldehyde under the Lewis acid-catalyzed reaction manifold.

Enantioselective route to 3-vinylidene tetrahydropyrans and 3-vinylidene oxepanes based on a silyl-Prins cyclization

A general method has been developed for the asymmetric synthesis of 3-vinylidene tetrahydropyrans and 3-vinylidene oxepanes based on the Lewis acid-catalyzed intramolecular reactions of oxocarbenium ions with propargylsilanes. The observed excellent diastereoselectivity and a high asymmetric induction offer a new synthetic method with a wide scope and generality.