Unusual C-alkylation of pyrazolines with 2-(het)arylcyclopropane-1,1-dicarboxylates in the presence of GaCl3

The reaction outcome between 2-(het)arylcyclopropane-1,1-dicarboxylates and 1- and 2-pyrazolinecarboxylates in the presence of GaCl3 is temperature-dependent: at 5°C 1:1 adducts are formed, whereas at 40°C 2:1 adducts would predominate.     

GaCl3-catalyzed formation of eight-membered rings from enynes bearing a cyclic olefin

GaCl3-catalyzed cycloisomerization of enynes having a cyclic olefin led to isolation of eight-membered ring compounds. [reaction: see text].     

Gold(I)-catalyzed formation of 3-pyrazolines through cycloaddition of diaziridine to alkynes

This work reports the high-yield formation of pyrazoline derivatives mediated by gold(I) catalysts. The reaction utilizes a diaziridine, which has seen only limited usage in organic methodology. Mechanistic studies suggest a gold-mediated opening of the diazridine ring, alkyne insertion, and finally an intramolecular hydroamination to furnish the product.     

Unexpected reaction of 4-bromo-2-bromomethyl-1,3-diselenolane with formation of divinyl selenide

Russian Journal of General Chemistry -     

Unexpected formation of 2-ethylthiophene by thermolysis of 1,1-dipropenylsulfide

Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, p. 561, April, 1988.     

Unexpected formation of 4-aryl-3-cyano-6-phenylpyridine-2(1H-thiones from the reaction of arylmethylenecyanothioacetamides with benzoyl-1,1,1-trifluoroacetone

4-Aryl-3-cyano-6-phenylpyridine-2(1H)-thiones, used in the synthesis of substituted 2-alkylthiopyridines, thieno[2,3-b]pyridines, and 1,4-di(pyridin-2-ylthio)butane, have been synthesized by the condensation of arylmethylenecyanothioacetamides with benzoyl-1,1,1-trifluoroacetone. The reaction path includes the formation of the Michael adduct which undergoes loss of the acyl group. The structure of 3-cyano-2-methylthio-4-(1-naphthyl)-6-phenylpyridine has been studied by X-ray crystallography. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, 1821–1828, December 2005.     

Unexpected reaction of 2-mercaptoquinoline with 4-hydroxy-4-methyl-2-pentynenitrile

Irkutsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1694–1695, December, 1995. Original article submitted November 21. 1995.     

Unexpected formation of tetrasubstituted 2,3-dihydrofurans from the reactions of beta-keto polyfluoroalkanesulfones with aldehydes

Catalyzed by piperidine, the reactions of beta-keto polyfluoroalkanesulfones with aromatic aldehydes afforded the unexpected tetrasubstituted 2,3-dihydrofurans in good yields, probably proceeding through the normal Knoevenagel condensation products. This reaction provided an efficient and novel method for the stereoselective synthesis of fluorine-containing tetrasubstituted trans-2,3-dihydrofurans.     

GaCl3- and TiCl4-catalyzed insertion of isocyanides into a C-S bond of dithioacetals

The insertion reaction of isocyanide into a C-S bond of dithioacetals is catalyzed by GaCl3 or TiCl4 to afford thioimidates containing an alpha-alkylthio group. Balanced thiophilicity of these Lewis acids is critical for efficient catalysis.     

Theoretical investigation on the GaCl3-catalyzed ring-closing metathesis reaction of N-2,3-butadienyl-2-propynyl-1-amine: three-membered ring versus four-membered ring mechanism

The gallium chloride (GaCl(3))-catalyzed ring-closing metathesis reaction mechanism of N-2,3-butadienyl-2-propynyl-1-amine has been studied at the Becke three-parameter hybrid functional combined with Lee-Yang-Parr correlation functional (B3LYP)/6-31G(d), B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p)//B3LYP/ 6-31G(d) and the second-order M?ller-Plesset perturbation (MP2)/6-311++G(d,p)//B3LYP/6-31+G(d,p) levels. It was found that the final metathesis product can be yielded via a three-membered or four-membered ring mechanism. The three-membered ring pathway is favorable due to its low energy barrier at the rate determining step. The whole reaction is stepwise and strongly exothermic.     

Equatorial preference in the C[bond]H activation of cycloalkanes: GaCl3-catalyzed aromatic alkylation reaction

GaCl(3) catalyzes the aromatic alkylation of naphthalene or phenanthrene using cycloalkanes. The C[bond]C formation predominantly takes place at the least hindered positions of the substrates, and equatorial isomers regarding the cycloalkane moiety are generally obtained. The reaction of bicyclo[4.4.0]decane and naphthalene occurs at the 2-position of naphthalene and at the 2- or 3-carbons of the cycloalkane, and the products possess a trans configuration at the junctures and an equatorial configuration at the naphthyl groups. Notably, cis-bicyclo[4.4.0]decane turns out to be much more reactive than the trans isomer, and a turnover number "TON" up to 20 based on GaCl(3) is attained. 1,2-Dimethylcyclohexane reacts similarly, and the cis isomer is more reactive than the trans isomer. Monoalkylcycloalkanes react at the secondary carbons provided that the alkyl group is smaller than tert-butyl. Adamantanes react at the tertiary 1-position. The alkylation reaction is considered to involve the C[bond]H activation of cycloalkanes with GaCl(3) at the tertiary center followed by the migration of carbocations and electrophilic aromatic substitution yielding thermodynamically stable products. The stereochemistry of the reaction reveals that GaCl(3) activates the equatorial tertiary C[bond]H rather than the axial tertiary C[bond]H.     

Synthesis of 3-Substituted Dialkyl 2-Aroyl-2-ethylcyclopropane-1,1-dicarboxylates by the Reformatsky Reaction

1-Aryl-2,2-dibromobutan-1-ones react with zinc and dialkyl arylmethylene- or isobutylidenemalonates to give dialkyl 2-aroyl-3-phenyl(isopropyl)-2-ethylcyclopropane-1,1-dicarboxylates which are formed mainly as Z isomers.     

[3+2] Cyclodimerization of 2-arylcyclopropane-1,1-diesters. Lewis acid induced reversion of cyclopropane umpolung

A novel Lewis acid catalyzed [3+2] cyclodimerization of 2-arylcyclopropane-1,1-dicarboxylates is reported. It is the first example of a reaction wherein a donor-acceptor cyclopropane provides two carbons in a newly formed ring. The described cyclodimerization represents a general convenient approach to polyfunctionalized cyclopentanes.     

Unexpected formation of an α-hydrazone in the reaction of perfluoro-4-methyl-2-pentene with hydrazine hydrate

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1463–1464, June, 1991.     

A GaCl3-catalyzed [4+1] cycloaddition of alpha,beta-unsaturated carbonyl compounds and isocyanides leading to unsaturated gamma-lactone derivatives

A GaCl3-catalyzed reaction of alpha,beta-unsaturated ketones with isocyanides leading to the formation of unsaturated lactone derivatives is described. This is the first example of the catalytic [4+1] cycloaddition of alpha,beta-unsaturated ketones and isocyanides. GaCl3 is an excellent catalyst due to its lower oxophilicity, which is desirable for all of the key steps, such as E/Z isomerization, cyclization, and deattachment from the products.     

1, 3-dipolar cycloaddition of C-phenyl carbamoyl-N-phenyl nitrone with some dialkyl-substituted 2-benzylidenecyclopropane-1,1-dicarboxylates: theoretical analysis of mechanism and regioselectivity

The regiochemistry of 1,3-dipolar cycloaddition reactions of C-phenyl carbamoyl-N-phenyl nitrone with some dialkyl-substituted 2-benzylidenecyclopropane-1,1-dicarboxylates as dipolarophile was investigated using density functional theory-based reactivity indexes and activation energy calculations at B3LYP/6-31G(d) level of theory. Analysis of the geometries and bond orders at the TS structures associated with the different reaction pathways shows that these 1,3-dipolar cycloaddition reactions occur via an asynchronous concerted mechanism. Analysis of the local electrophilicity and nucleophilicity indexes based on Parr functions only for reaction between 1 + 2a and based on Fukui functions only for 1 + 2b gives correct regioselectivity. The theoretical results obtained in the work clearly predict the regiochemistry of the isolated cycloadducts and agree to experimental results.