(Dicyclopentadiene) platinum(II) dichloride: An efficient catalyst for the hydrosilylation reaction between alkenes and triethoxysilane

(Dicyclopentadiene) platinum(II) dichloride was found to be an efficient hydrosilylation catalyst (homogeneous) upon a wide variety of functionalized alkenes and alkenes terminated with chemical moieties (diphenyl amino-, N-carbazol- and N-isoindoline-1,3-dione-). It is noteworthy that the hydrosilylation of aminated alkenes with triethoxysilane exhibited the yield of over 70% and the selectivity (γ-isomer/β-isomer) of more than 3/1. Due to steric hindrance lowering Markovnikov probability, the alkenes with big terminal moieties (diphenyl amino-, N-carbazol- and N-isoindoline-1,3-dione-) presented the high ratio of anti-Markovnikov isomers. The strategy of the hydrosilylation of the protected diamino chelating alkene was developed.     

Rhodium-catalyzed hydroformylation of olefins: Effect of [bis(2,4-di-tert-butyl) pentaerythritol] diphosphite (alkanox P-24) on the regioselectivity of the reaction

Rhodium (I) associated with [bis(2,4-di-tert-butyl) pentaerythritol] diphosphite (I) as a ligand represents an active catalyst system for highly regioselective hydroformylation of various alkenes. The commercially available bis(2,4-di-tert-butyl)pentaerythritol diphosphite (alkanox P-24) (I), which has been used so far as an antioxidant in the stabilization of polymers, was used as a diphosphite ligand for the selective hydroformylation reaction of olefins. Excellent selectivity towards linear aldehydes and excellent conversions were achieved in the hydroformylation of alkenes. The hydroformylation reaction was applied to various olefinic substrates including the internal alkenes.     

Observations on the direct amidocyclopropanation of alkenes using organozinc carbenoids

A series of amidocyclopropanes were prepared by direct amidocyclopropanation of alkenes, using organozinc carbenoids generated from readily available diethoxymethylamides. The amidocyclopropanation of monosubstituted alkenes led to selective formation of the trans-amidocyclopropane in most cases, but with more substituted alkenes, the stereochemical outcome of the cyclopropanation reactions was unpredictable. The amidocyclopropane products can be readily elaborated to structurally interesting cyclopropane containing amino acids or amino alcohols.     

Palladium-catalyzed aziridination of alkenes using N,N-dichloro-p-toluenesulfonamide as nitrogen source

N,N-Dichloro-p-toluenesulfonamide (TsNCl₂) was found to be an efficient nitrogen source for the aziridination of unfunctionalized alkenes using palladium catalysts. Among the palladium salts, palladium acetate was the most effective catalyst for this reaction. A variety of alkenes were reacted at room temperature with TsNCl₂ to form the desired aziridines in moderate to good yields. This method can complement our previous protocol which is limited to the use of electron-deficient α,β-unsaturated alkenes.     

Lanthanum metal-assisted cyclopropanation of alkenes with gem-dihaloalkanes

It was confirmed that lanthanum metal was an efficient reagent for the reductive dehalogenation of gem-dihaloalkanes. When gem-dihaloalkanes were allowed to react with lanthanum metal in the presence of alkenes, cyclopropanation of the alkenes occurred under mild conditions giving the corresponding cyclopropanes in moderate to good yields.     

N-Amino-endo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboximide in reaction of oxidative aminoaziridination

The ability of easily accessible N-amino-endo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboximide to undergo oxidative addition to double bonds of alkenes has been explored. The compound is active toward alkenes with electron-withdrawing groups, aryl- and alkyl-substituted alkenes, providing access to stable derivatives of N-aminoaziridine. Yields varied from 20% to 70%. No products of self-aminoaziridination were isolated.     

Synthesis of fluorinated N-aminoaziridines: access to new CF3-peptidomimetics

A series of fluorinated N-aminoaziridines have been synthesized by the PhI(OAc)₂-mediated aziridination procedure. The reaction was carried out with various protected hydrazides and fluorinated alkenes. The reaction was extended to alkenes bearing an amino acid and the ring opening of the CF₃–N-aminoaziridines has been investigated.     

A novel highly regio- and diastereoselective haloamination of alkenes catalyzed by divalent palladium

From the readily available allylic alcohols or allylic amines, a novel Pd(II)-CuCl₂-catalyzed haloamination reaction of alkenes with high chemo-, regio-, and diastereo-selectivity was developed. The reaction proceeds through trans-aminopalladation of alkenes, followed by oxidative cleavage of the carbon-palladium bond with retention of configuration.     

Stereoselective synthesis of N-protected pyrrolidines via Pd-catalyzed reactions of γ-(N-acylamino) alkenes and γ-(N-Boc-amino) alkenes with aryl bromides

The stereoselective synthesis of N-acyl- and N-Boc-protected pyrrolidines via Pd-catalyzed reactions of γ-(N-acylamino) alkenes and γ-(N-Boc-amino) alkenes with aryl bromides is described. These reactions effect formation of two bonds in a single operation and proceed with generally high levels of diastereoselectivity. In contrast to previously described reactions of γ-(N-arylamino) alkenes, these transformations proceed in high yield and high regioselectivity with both electron-rich and electron-deficient aryl bromides as well as vinyl bromide substrates.     

CuI/glycerol mediated stereoselective synthesis of 1,2-bis-chalcogen alkenes from terminal alkynes: synthesis of new antioxidants

(E)-1,2-Bis-chalcogen alkenes were stereoselectively prepared in good yields by the addition of diorganyl dichalcogenides to terminal alkynes using CuI/Zn/glycerol as a recyclable catalytic system. The antioxidant activity in vitro of four (E)-1,2-bis-chalcogen alkenes synthesized was evaluated and (E)-1,2-bis-(4-methoxyphenylselanyl)styrene 3b presented excellent activity. The catalytic system used in the synthesis was recovered and used directly up to 5 cycles without loss of activity.     

Tetraphosphine/palladium-catalyzed Heck reactions of aryl halides with disubstituted alkenes

cis,cis,cis-1,2,3,4-Tetrakis(diphenylphosphinomethyl)cyclopentane/[PdCl(C₃H₅)]₂ efficiently catalyses the Heck reaction of disubstituted alkenes such as methyl crotonate, ethyl cinnamate, methyl methacrylate or α-methylstyrene with a variety of aryl halides. In the presence of 1,2-disubstituted alkenes the stereoselectivities of the reactions strongly depend on the substituents of the alkenes. Selectivities up to 97% in favor of E-isomers can be obtained for the addition to methyl crotonate. With the 1,1-disubstituted alkenes methyl methacrylate or α-methylstyrene mixtures of products are obtained.     

Cyclisation of α-chiral aminyl radicals

α-Chiral aminyl radicals have been generated from sulfenamides of α-amino acid esters and α-phenylethylamine using Bu₃SnH. The aminyl radicals of α-amino acid esters undergo 5-exo-trig cyclisation reactions onto side chain alkenes to yield proline analogues with reasonable diastereoselectivity. Preliminary studies show urethanyl radicals generated from sulfenamides of alkenyl urethane derivatives of α-amino acid esters and α-phenylethylamine undergo 5-exo-rig cyclisations to providing a protocol for the radical amination of unactivated alkenes. The α-ester of the amino acid or the urethane groups impart electrophilic behaviour to the aminyl radicals and facilitates cyclisation onto alkenes.     

Reaction of alkenes and dienes with t-butylmagnesium halides and zirconocene dihalides. A convenient procedure for hydrozirconation and a novel t-butylzirconation of conjugated alkenes

The reaction of nonconjugated monosubstituted alkenes with t-BuMgCl and Cl₂ZrCp₂ at room temperature produces the corresponding monoalkylzirconium derivatives in high yields, while conjugated alkenes undergo either a novel t-butylzirconation or hydrozirconation depending on the reaction conditions.     

Isomerization of alkenes in the presence of Pd(acac)2-BF3OEt2 catalytic system

Positional isomerization of alkenes was studied in the presence of Pd(acac)₂ + 20BF₃OEt₂ catalytic system. The reactivity of alkenes decreases in the following order: 1-hexene > 1-heptene > 2-methyl-1-pentene > 4-methyl-2-pentene (cis + trans).     

Metal triflate catalyzed highly regio- and stereoselective 1,2-bromoazidation of alkenes using NBS and TMSN3 as the bromine and azide sources

Metal triflate catalyzed 1,2-bromoazidation of alkenes was performed using N-bromosuccinimide (NBS) and trimethylsilyl azide (TMSN₃) as the bromine and azide sources, respectively. Among the metal triflates, Zn(OTf)₂ was found to be the best catalyst. This catalytic process represents a highly regioselective, stereoselective and high yielding method for the synthesis of anti-1,2-bromoazides from a variety of alkenes including α,β-unsaturated carbonyl compounds.     

Addition of aldehydes and their equivalents to electron-deficient alkenes using N-hydroxyphthalimide (NHPI) as a polarity-reversal catalyst

Radical addition of aldehydes and masked aldehydes like 1,3-dioxolanes to electron-deficient alkenes was achieved by the use of catalytic amounts of BPO and N-hydroxyphthalimide (NHPI) as a polarity-reversal catalyst under mild conditions. Three-component radical coupling of 1,3-dioxolanes, maleates, and alkenes was performed in the presence of BPO and NHPI under similar conditions.     

Synthesis of dihydrofurans containing trifluoromethyl ketone and heterocycles by radical cyclization of fluorinated 1,3-dicarbonyl compounds with 2-thienyl and 2-furyl substituted alkenes

Manganese(III) acetate based radical cyclization of various fluorinated 1,3-dicarbonyl compounds with 2-thienyl and 2-furyl substituted alkenes produced 3-trifluoroacetyl and 2-trifluoromethyl-dihydrofurans in good yields. The radical cyclizations of 2-methyl-5-[(E)-2-phenylvinyl]furan 2b and 2-[(E)-2-phenylvinyl]thiophene 2c led to the formations of 5-(5-methyl-2-furyl)-4,5-dihydrofuran and 5-(2-thienyl)-4,5-dihydrofuran, respectively. In the reactions of 1,3-dicarbonyls with alkenes, 2-thienyl substituted alkenes formed 4,5-dihydrofurans in higher yields than 2-furyl substituted alkenes.     

Reaction of CBrF2-CBrF2 with hydrazones of aromatic aldehydes: Novel efficient synthesis of fluorocontaining alkanes, alkenes and alkynes

An olefination of hydrazones of aromatic aldehydes by CBrF₂-CBrF₂ under copper catalysis was investigated. In situ prepared aldehydes hydrazones were converted to (3-bromo-2,2,3,3-tetrafluoropropyl)arenes by reaction with CBrF₂-CBrF₂ in the presence of CuCl. Subsequent elimination of HF by sodium hydroxide resulted in stereospecific formation of fluorocontaining alkenes. Elimination proceeds stereoselectively, only Z-isomers of alkenes are formed. Elimination of two molecules of HF from (3-bromo-2,2,3,3-tetrafluoropropyl)arenes by treatment with potassium tert-butoxide leads to formation of (bromodifluoromethyl)alkynes. As a result a simple and efficient transformation of aromatic aldehydes to range of various fluorinated alkanes, alkenes and alkynes was elaborated.     

Synthesis of highly substituted pyrrolidines via palladium-catalyzed cyclization of 5-vinyloxazolidinones and activated alkenes

N-Tosyl-5,5-divinyloxazolidin-2-one undergoes a palladium-catalyzed decarboxylative cyclization across a range of electrophilic alkenes to give the corresponding pyrrolidine derivatives bearing two contiguous quaternary centres. Alkenes bearing two electron-withdrawing groups are required; pyrrolidines were not formed from mono-activated alkenes. Bulky, electron-rich phosphines promote pyrrolidine formation with less highly electrophilic, doubly activated alkenes, and a dramatic improvement is observed in the presence of iodide.     

Palladium-catalyzed convenient one-pot synthesis of multi-substituted 2-pyrones via transesterification and alkenylation of enynoates

An efficient one-pot protocol for the synthesis of multi-substituted 2-pyrone derivatives from internal alkynes and unactivated alkenes is reported. The methodology involves difunctionalization of internal alkynes by using Pd(II) as a catalyst alongwith X-Phos as ligand via 6-endo transesterification and subsequent alkenylation pathway. Notable features include simple and easily available starting materials, including a range of unactivated alkenes, reduced synthetic steps and mild reaction conditions with high efficiency.