Regio- and stereoselective lithiation of 2,3-diphenylaziridines: a multinuclear NMR investigation

The alpha-lithiation-trapping sequence of trans-N-alkyl-2,3-diphenylaziridines (s-BuLi or s-BuLi/TMEDA), taking place with a stereochemistry which dramatically depends on the solvent coordinating ability (inversion of configuration in THF and retention in toluene), has been carefully investigated. 1H,13C, and 7Li multinuclear NMR investigations at low temperature suggest that two differently configured lithiated aziridines (monomeric cis-1-Li in THF and dimeric trans-1-Li in toluene) are involved.     

Regio- and stereoselective lithiation of terminal oxazolinylaziridines: the aziridine N-substituent and the oxazolinyl group effect

The regioselective lithiation of terminal oxazolinylaziridines has been investigated. The steric hindrance of the nitrogen substituent in 1-trityl-2-oxazolinylaziridine 3a, combined with the coordinating ability of the oxazolinyl group, causes beta-lithiation, whereas a completely regioselective alpha-lithiation is observed with the much less sterically demanding 1-benzyl-2-oxazolinylaziridine 3c and a competition between alpha- and beta-lithiation occurs with 1-cumyl-2-oxazolinylaziridine 3b in which the N-substituent has a steric hindrance in between the trityl and the benzyl groups. The application of the lithiation-trapping sequence for the preparation of enantioenriched 2,3-cis-disubstituted oxazolinylaziridines and aziridino-gamma-lactones is also reported.     

Regio- and stereoselective synthesis of isoindolin-1-ones via electrophilic cyclization

[reaction: see text] A variety of substituted isoindolin-1-ones are readily prepared in good to excellent yields under very mild reaction conditions by the reaction of o-(1-alkynyl)benzamides with ICl, I(2), and NBS. In a few cases, substituted isoquinolin-1-ones were obtained as the major product instead. This methodology accommodates various alkynyl amides and functional groups and has been successfully extended to heterocyclic starting materials. This chemistry has been successfully applied to the synthesis of a biologically interesting alkaloid, cepharanone B.     

Regio- and stereoselective reactions of gem-difluorinated vinyloxiranes with heteronucleophiles

[Reaction: see text]. Regio- and stereoselectivity in reactions of gem-difluorinated vinyloxiranes with heteronucleophiles were successfully controlled. Halogen atoms were introduced regioselectively at the allylic epoxide carbon with an inversion in stereochemistry using MgBr2*Et2O or Li2CuCl4 to produce anti-vic-halohydrine. The other diastereomers were obtained selectively using LiBr/AcOH or BCl3, and SN2' type products were formed selectively with excellent E preference by changing the reaction temperature. Moreover, a further investigation led us to find that a regio- and stereoselective SN2' addition of several Brnsted acids was dependent on the pKa values of the acids. Under strong acidic conditions, we exclusively obtained E allylic alcohols.     

Regio- and stereoselective copper-catalyzed carbozincation reactions of alkynyl sulfoximines and sulfones

[structure: see text]. Stereochemically pure polysubstituted vinyl sulfoximines and sulfones are easily prepared by a copper-catalyzed syn carbozincation reaction of the corresponding alkynyl derivatives.     

Synthesis and some electrophilic substitution reactions of 2-phenyloxazole

A new synthesis of 2-phenyloxazole that includes the preparation of 2-phenyloxazoline and aromatization of the latter by the action of nickel peroxide was developed. It was established that under conditions that exclude protonation electrophilic substitution reactions are directed to the oxazole ring of 2-phenyloxazole; the 5 position is considerably more active than the 4 position.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 881–884, July, 1984     

Phase-transfer catalysis in reactions of electrophilic aromatic substitution

Electrophilic substitution in aromatic compounds under conditions of phase-transfer catalysis is considered. Catalysts of phase transfer of electrophilic reagents are used; their efficiency and the mechanism of their action in organic solvent-water systems are discussed.This review is based on materials of the report delivered at the Conference Phase-Transfer Catalysis. New Ideas and Methods (March 1994).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1895–1900, October, 1995.     

Generation and electrophilic substitution reactions of 3-lithio-2-methyleneaziridines

2-Methyleneaziridinyl anions can be produced by selective deprotonation of the parent aziridine at C-3 using sec-BuLi/TMEDA. Subsequent reaction with a wide variety of electrophiles including MeI, ICH₂CH₂CH₂CH₂Cl, PhCH₂Br, allyl bromide, Me₃SiCl, Bu₃SnCl, PhCHO and Ph₂CO provides the corresponding C-3 substituted derivatives in moderate to good yields (43-91%). In the case of homochiral methyleneaziridines bearing an (S)-α-methylbenzyl group on nitrogen, high levels of diastereocontrol (up to 90%de) can be achieved in this lithiation/alkylation sequence.     

Steric factor in electrophilic substitution reactions of aromatic hydrocarbons

Summary In supplementation of previous work on halomethylation reactions, the nitration, chlorination, bromination, and iodination of toluene, ethylbenzene, and eumene were investigated. By the method of oxidizing the derivatives formed, the relative amounts of o- and p-isomers were determined quantitatively, and the results reveal the steric effects of substituents in the aromatic nucleus on orientation in all of the above-mentioned electrophilic substitution reactions.     

Regio- and stereoselective reactions between cyclic Baylis-Hillman type adducts and N-nucleophiles and P-nucleophile

New important organic compounds multifunctionalized cyclic 6-membered and 7-membered allylic amines, azide and phosphonates have been obtained via regio- and diastereoselective reactions of cyclic Baylis-Hillman type adducts 1 with N-nucleophiles and P-nucleophile. We have found that the reactions proceed by S_N2 or S_N2′ processes exclusively, or by both processes simultaneously. The S_N2′ process occurs with anti stereochemistry.     

Regio- and stereoselective hydrophosphination reactions of alkynes with phosphine-boranes: access to stereodefined vinylphosphine derivatives

Vinylphosphine-borane complexes are easily synthesized by regio- and stereoselective hydrophosphination of terminal alkynes with use of secondary phosphine-boranes as hydrophosphinating agent. The regioselectivity of the reaction is efficiently controlled by the choice of the activation process: thermal or metal catalyst activation. The vinylphosphine derivatives are purified by chromatography on silica gel. Scalability of the process is demonstrated on a gram scale. This simple route should promote the use of vinylphosphines as building blocks for organic and organometallic chemistry.     

Regio- and stereoselective synthesis of 2-deoxy-C-aryl glycosides via palladium catalyzed decarboxylative reactions

An efficient and versatile approach for the synthesis of 2-deoxy-C-aryl glycosides is reported. This strategy is based on a palladium-catalyzed decarboxylative Heck coupling reaction of benzoic acids and glycals. A wide variety of glycals and benzoic acids have been screened, and all these reactions could afford the desired C-aryl glycoside products in moderate to good yields with exclusive regio- and stereoselectivities.     

Regio- and stereoselective ring-opening reactions of epoxides with indoles and pyrroles in 2,2,2-trifluoroethanol

Aliphatic and aromatic epoxides react regio- and stereoselectively with indoles and pyrroles in 2,2,2-trifluoroethanol without the use of a catalyst or any other additive. While aromatic epoxides are selectively attacked at the benzylic position, aliphatic epoxides react at the less-substituted position. Chiral epoxides react with >99 % ee (ee=enantiomeric excess).     

Relationships and features of electrophilic substitution reactions in the azole series

On the basis of an analysis of the results from quantum-chemical calculation of model systems, together with published experimental data, a study has been made of the influence of the structure of azoles on their capability for electrophilic substitution reactions proceedings either through the traditiional addition-abstraction mechanism or through the formation of ylides.     

Synthesis of symmetrical and unsymmetrical diindolylmethanes via acid-catalysed electrophilic substitution reactions

A range of activated indole-2-carboxylate derivatives was prepared via the Hemetsberger indole synthesis. Vilsmeier formylation was explored to establish regioselectivity and to prepare a range of new indole carbaldehydes. The indole aldehydes were reduced to the corresponding hydroxymethylindoles in good yields by the use of sodium borohydride in THF. Symmetrical 4,4′-, 6,6′- and 7,7′-diindolylmethanes were prepared via the acid-catalysed reaction of the corresponding hydroxymethylindoles. Furthermore, the treatment of methyl 4-hydroxymethyl-5,6-dimethoxyindole-2-carboxylate and a range of methyl indole esters with acetic acid led to the formation of unsymmetrical 4,6′- and 4,7′-dindolylmethanes.     

Regio- and stereoselective reductions of gem-difluorinated vinyloxiranes

[reaction: see text] gem-Difluorinated vinyloxiranes are versatile building blocks for the synthesis of fluorinated compounds. Investigations of their reactions with nucleophiles resulted in highly regio- and stereoselective reductions. In their reactions with LiAlH4, hydride reacted at the allylic epoxide carbon to produce homoallylic alcohols exclusively. Moreover, regio- and stereoselective S(N)2' reactions were observed with DIBAL-H and BH3 x THF; the former afforded E allylic alcohols, whereas the latter furnished the corresponding Z isomers with excellent selectivities.     

Regio- and stereoselective synthesis of 1,4-dienes

Titanocene(II)-promoted cross-coupling between (Z)-alkenyl methyl sulfones and terminal allenes produced 1,4-dienes regioselectively via the formation of 2-alkylidenetitanacyclopentanes. Preferential formation of E,Z-dienes was observed in the reaction using aryl-, amino-, and phosphinylallenes.