Fe(III)/NaBH(4)-Mediated Free Radical Hydrofluorination of Unactivated Alkenes

A powerful Fe(III)/NaBH(4)-mediated free radical hydrofluorination of unactivated alkenes is disclosed using Selectfluor reagent as a source of fluorine and resulting in exclusive Markovnikov addition. In contrast to the traditional and unmanageable free radical hydrofluorination of alkenes, the Fe(III)/NaBH(4)-mediated reaction is conducted under exceptionally mild reaction conditions (0 °C, 5 min, CH(3)CN/H(2)O). The reaction can be conducted open to the air and with water as a cosolvent and demonstrates an outstanding substrate scope and functional group tolerance.     

Rh(III)-catalyzed oxidative coupling of unactivated alkenes via C-H activation

Oxime directed aromatic C-H bond activation and oxidative coupling to alkenes is reported using a cationic Rh(III) catalyst. Significantly, the method can be used to oxidatively couple unactivated, aliphatic alkenes.     

Iron(II)/copper(I)-mediated stereoselective carbozincation of ynamides. One-pot synthesis of α-allyl-tetrasubstituted-enamides

The iron(II) chloride- and copper(I) iodide-mediated carbozincation of a panel of substituted ynamides is described in this article. The reaction is totally regio- and stereoselective. Experiments showed that the reaction mediated with Fe(II) was more substrate dependent than the reaction performed with Cu(I). Interestingly, in the presence of allylbromide, stereoselective carboallylation can be achieved for the first time in a one-pot procedure, leading to skipped dienamides.     

syn additions to 4alpha-epoxypyranosides: synthesis of L-idopyranosides

The syn-selective addition of organozinc compounds to 4alpha-epoxypyranosides (4alpha-EPs), generated from methyl beta-D-glucoside or aminoglucoside, provides an efficient route to pyranosides with alpha-L-ido configurations, including L-iduronic acid, neosamine B, and higher monosaccharide derivatives.     

Highly efficient gold(III)-catalyzed intermolecular hydroarylation of unactivated alkenes with arenes under mild conditions

A simple and efficient method for functionalization of electron-rich arenes and heteroarenes with unactivated alkenes by Au(III)-catalyzed intermolecular hydroarylation under mild reaction conditions was developed. This method features a short reaction time (5 h) under mild conditions and has a broad substrate scope, including electron-rich arenes and heteroarenes, terminal and internal substituted aryl alkenes, and unactivated aliphatic alkenes.     

Electrochemical Behavior of Iron(III)/Iron(II) Couple in Dimethylformamide

The electrochemical behavior of the iron(III)/iron(II) couple was investigated in both complexing (Cl⁻) and noncomplexing (ClO⁻₄) media in dimethylformamide (DMF), and the results were compared with the results obtained in aqueous solutions. The diffusion coefficients for iron(III) and iron(II) in DMF are larger in complexing medium than in noncomplexing medium, contrary to the results obtained in aqueous solutions. The heterogeneous electron transfer rate constants for the iron(III)/iron(II) couple obtained in DMF were found to be smaller in DMF solution as a result of the specific adsorption of DMF. The formal potential of the Fe(III)/Fe(II) couple in DMF is about 0.2 V less positive in noncomplexing medium as a result of the greater stabilization of iron(III) by the strongly cation-solvating DMF. The formal potential of the same couple in complexing medium (Cl⁻) was found to be 0.5 V less positive due to a combination of solvation and complexation effects. Cyclic voltammetric investigations show a quasi-reversible electron transfer without any coupled chemical reaction.     

Rh(III)-catalyzed oxidative olefination of N-(1-naphthyl)sulfonamides using activated and unactivated alkenes

Rhodium(III)-catalyzed oxidative olefination of N-(1-naphthyl)sulfonamides has been achieved at the peri position. Three categories of olefins have been successfully applied. Activated olefins reacted to afford five-membered azacycles as a result of oxidative olefination-hydroamination. Unactivated olefins reacted to give the olefination product. 2-fold oxidative C-C and C-N coupling was achieved for allylbenzenes.     

Manganese(III)-mediated intermolecular cyclization reactions of alkenes and active methylene compounds

The reactions of 1,1-diphenylethene, 1,1-bis(4-chlorophenyl)ethene, 1,1-bis(4-methylphenyl)ethene, and 1,1-bis(4-methoxyphenyl)ethene with 3,5-diacetyl-2,6-heptanedione in the presence of manganese(III) acetate in acetic acid at 80° yielded 4,6-diacetyl-8,8-diaryl-1,3-dimethyl-2,9-dioxabicyclo[4.3.0]non-3-enes (41-48%), 5-acetyl-2,2-diaryl-6-methyl-2,3-dihydrobenzo[b]furans (20–21%), 3-acetyl-5,5-diaryl-2-methyl-4,5-dihydrofurans (5–10%), and benzophenones (3–7%). Similarly, the reactions of 1,1-diarylethenes with dimethyl 2,4-diacetyl-1,5-pentanedioate or diethyl 2,4-diacetyl-1,5-pentanedioate gave the corresponding 4,6-bis(alkoxycarbonyl)-8,8-diaryl-1,3-dimethyl-2,9-dioxabicyclo[4.3.0]non-3-enes in moderate yields.     

Manganese(III)-mediated oxidative free-radical additions of 1,3-dicarbonyl compounds to homobenzonorbornadiene and benzobarrelene: mechanistic studies

Homobenzonorbornadiene and benzobarrelene were reacted with dimedone/acetylacetone and Mn(OAc)₃ in the presence of Cu(OAc)₂ in acetic acid. Mainly rearranged products having a [2.2.2]skeleton and the nonrearranged dihydrofuran derivatives were obtained. These observations clearly indicated that the second oxidation takes place before the cyclization reaction. Furthermore, intramolecular tandem oxidations were observed where unusually oxyl radicals attack the double bond to form the products. The mechanism of the formation of the products is discussed.     

An unprecedented methylene oxidation accompanying the aza Diels-Alder reactions of acyclic unactivated alkenes: synthesis of novel quinolin-3-one substituted pyrimidinone derivatives

The regioselective aza Diels-Alder reactions of isopropenyl pyrimidinone with N-arylimines in the presence of Y/Sc triflates as catalyst are described. An unprecedented oxidation of methylene to carbonyl occurred resulting in exclusive formation of 6-oxo-1,6-dihydropyrimidin-5-yl-4H-quinolin-3-one derivatives.     

Osmium (VIII)-mediated oxidation of arsenic (III)/antimony (III) by 1-equivalent oxidants

Os(VIII) catalysis of oxidation of As(III)/Sb(III) by 1-equivalent oxidants like Ce(IV) and Mn(III) in acid medium is studied. A multistep mechanism involving the intervention of the intermediate oxidation states of osmium is found to apply. Specific rates of different steps in the mechanism are estimated and used to calculate reaction rates which are in reasonable agreement with those of experiment.     

Thiophenol additions to alkenylidenecyclopropanes. A novel synthesis of karahanaenone

The additions of thiophenol to alkenylidenecyclopropanes (e.g. 3, 14) are found to be highly regioselective and stereoselective leading to $\text{endo}$- (or $\text{cis}$- vinyl sulphide adducts (e.g. 4, 15) resulting from additions to the 1,4-double bonds in the starting materials. Thiophenol addition to (1) leads to a mixture of the vinyl sulphides (16) and (17) which undergo Cope rearrangement producing the cycloheptadiene (18); hydrolysis of (18) then gives karahanaenone (19) an odoriferous constituent of Japanese hop and Cypress oil.     

Iron(III) porphyrin catalyzed aziridination of alkenes with bromamine-T as nitrene source

[reaction: see text] Iron(III) porphyrin complexes Fe(Por)Cl are effective catalysts for aziridination of alkenes using bromamine-T as the nitrene source. The catalytic system can operate under mild conditions with alkenes as limiting reagents. The aziridination reaction is general and suitable for a wide variety of alkenes, including aromatic, aliphatic, cyclic, and acyclic olefins, as well as alpha,beta-unsaturated esters. For 1,2-disubstituted olefins, the reactions proceeded with moderate to low stereospecificity.     

Efficient addition of alcohols, amines and phenol to unactivated alkenes by Au(III) or Pd(II) stabilized by CuCl2

The nucleophilic addition of alcohols, amines and phenol to unactivated alkenes catalyzed by cationic gold and palladium becomes limited due to the fast reduction into metallic gold under reaction conditions. The presence of CuCl2 retards the reduction of Au(III) and Pd", strongly increasing the turnover number of gold and palladium catalysts. It is shown that new Au(III)-CuCl2 and Pd(II)-CuCl2 catalysts are active and selective for the nucleophilic addition of alcohols, amines and phenol to unactivated alkenes.     

Reduction of iridoid aglycones—III: Reactivity of lamiolgenin towards NaBH4

The reaction which occurs when lamiolgenin 2 is treated with an excess of NaBH₄ is unusually complex owing to an intramolecular aldolic condensation which leads to a bicyclo[3.2.0]heptane derivative 4. The mechanism of this reduction has been investigated by using NaBD₄. Spectral data (IR, ¹H NMR, ¹³ C NMR) of the products are presented.     

Unusual manganese(III)-mediated oxidative free radical additions of 1,3-dicarbonyl compounds to benzonorbornadiene and 7-heterobenzonorbornadienes: mechanistic studies

Benzonorbornadiene and heterobenzonorbornadiene were reacted with dimedone/acetylacetone and Mn(OAc)3 in the presence and absence of Cu(OAc)2. The reaction of benzonorbornadiene with dimedone gave mainly the dihydrofuran addition product, whereas the reaction with acetylacetone produced a rearranged product in addition to the dihydrofuran derivative. On the other hand, oxanorbornadiene gave unusual products such as the cycloproponated compound and a product arising from the incorporation of 2 mol of dimedone. The reaction of azanorbornadiene with 1,3-dicarbonyl compounds and Mn(OAc)3 always produced rearranged products. The mechanism of formation of the products is discussed. We generally observe that the cyclization reaction takes place after the oxidation of the initially formed radical.     

Iron(III)-promoted aza-Prins-cyclization: direct synthesis of six-membered azacycles

[reaction: see text] A new iron(III) halide-promoted aza-Prins cyclization between gamma,delta-unsaturated tosylamines and aldehydes provides six-membered azacycles in good to excellent yields. The process is based on the consecutive generation of gamma-unsaturated-iminium ion and further nucleophilic attack by the unsaturated carbon-carbon bond. Homoallyl tosylamine leads to trans-2-alkyl-4-halo-1-tosylpiperidine as the major isomer. In addition, the alkyne aza-Prins cyclization between homopropargyl tosylamine and aldehydes gives 2-alkyl-4-halo-1-tosyl-1,2,5,6-tetrahydropyridines as the only cyclic products.     

Mn(III)/Cu(II)-mediated oxidative radical cyclization of alpha-(Methylthio)acetamides leading to erythrinanes

Treatment of N-[2-(3,4-dimethoxyphenyl)ethyl]-alpha-(methylthio)acetamide 3 with Mn(OAc)3 in the presence of Cu(OAc)2 gave tetrahydroindol-2-one 4, which then cyclized with Mn(OAc)3 to give 4-acetoxyerythrinane 5. A similar reaction of the 3,4-methylenedioxyphenyl congener 8 also gave tetrahydroindol-2-one 9, which, however, gave only a trace amount of the Mn(OAc)3-mediated cyclization product 11 and afforded the oxidation product 10. On the basis of these results, formation of 5 from 4 was thought to proceed via nucleophilic attack of the pyrrole ring on the cation-radical lX, generated by a single electron-transfer reaction of the acetoxy-substituted intermediate V. Treatment of compound 16 with Mn(OAc)3/Cu(OAc)2 gave no erythrinane derivative with recovery of the starting material, indicating that the presence of a methylthio group of 4 is essential for effecting the formation of erythrinane 5. On the other hand, treatment of 3 with Mn(OAc)3 using Cu(OTf)2 as an additive in place of Cu(OAc)2 gave another erythrinane 17. This method was applied to a formal synthesis of 3-demethoxyerythratidinone (20), a naturally occurring Erythrina alkaloid.     

Organic reactions in water: an efficient zinc-mediated stereoselective synthesis of (E)- and (Z)-trisubstituted alkenes using unactivated alkyl halides

[reaction: see text] Treatment of the acetyl derivatives of the Baylis-Hillman adducts 3-hydroxy-2-methylene-alkanoates and 3-hydroxy-2-methylene-alkanenitriles with unactivated alkyl halides in the presence of Zn in saturated aqueous NH(4)Cl solution at room temperature afforded (2E)-2-substituted-alk-2-enoates in the first case and (2Z)-2-substituted-alk-2-enenitriles with high (Z)-selectivity in the second case.