A mild oxidative aryl radical addition into alkenes by aerobic oxidation of arylhydrazines

A mild and practical oxyarylation of alkenes by oxidative radical addition has been developed by using aerobic oxidation of hydrazine compounds. The use of a catalytic amount of potassium ferrocyanide trihydrate (K₄[Fe(CN)₆]?3 H₂O) and water accelerated this radical reaction to give peroxides or alcohols from simple alkenes in good yields. The environmentally friendly and economical radical reactions were achieved at room temperature in the presence of iron catalyst, oxygen gas, and water. A method involving aniline as a radical precursor is also described.     

Mono- and bisadducts from the addition of thianthrene cation radical salts to cycloalkenes and alkenes

Thianthrene cation radical salts, Th(*)(+) X(-)(X(-) = a, ClO(4)(-); b, PF(6)(-); c, SbF(6)(-)), add to cycloalkenes (C(5)-C(8)) in acetonitrile (MeCN) to form 1,2-bis(5-thianthreniumyl)cycloalkane salts and 1,2-(5,10-thianthreniumdiyl)cycloalkane salts, most of which have now been isolated and characterized. These are called bis- (3, 6, 9, 12) and monoadducts (4, 7, 10, 13). The proportional amount of the monoadduct obtained in the initial stage of the reaction varied with the cycloalkene in the order C(6) < C(5) < C(7) < C(8). Thus, the ratio bis:mono for C(5) and C(7) was, respectively, about 80/20 and 50/50. In contrast, only about 5% of the C(6) monoadduct (7a) and none of 7b,c was obtained, while for C(8) none of the bisadducts 12a-c was found. Bisadducts 3 and 9 lost thianthrene (Th) slowly in MeCN solution and changed into monoadducts 4 and 10. A comparable change from 6a into 7a was not observed. The monoadducts, themselves, lost a proton slowly in dry MeCN and opened into 1-(5-thianthreniumyl)cycloalkenes (5, 8, 11, 14). With 3 and 9, particularly, it was possible to follow with NMR spectroscopy the succession of changes, for example, 3 to 4 to 5. The opening of a monoadduct was made faster by adding a small amount of water to the solution. The bisadducts of 4-methylcyclohexene (15a) and 1,5-cyclooctadiene (17a) were isolated and characterized. Although a small amount of monodduct (16a) of 4-methylcyclohexene was found with NMR spectroscopy, it could not be isolated. Bis- and monoadducts were obtained also in additions of Th(*)(+) ClO(4)(-) to acyclic alkenes, in relative amounts that, again, varied with the alkene. From cis-2-butene the dominant product was the bisadduct (18), while the monoaduct (19) was characterized with NMR spectroscopy but could not be isolated. In contrast, trans-3-hexene gave mainly the monoadduct (21), while the bis adduct (20) could not be isolated. With 4-methyl-cis-2-pentene, both bis- (22) and monoadduct (23) were isolated, the former being dominant. The conversion of 18 into 19 was characterized with NMR spectroscopy. In all cycloalkene bisadducts, the configurational relationship of the two thianthrenium groups was trans, while in the monoadducts, the bonds to the single thianthrene dication were (necessarily) cis. In both bis- and monoadducts of acyclic alkenes, the configuration of the alkene was retained. The mechanisms of addition with retention of configuration, of conversion of a bis- into a monoadduct, and of opening of a monoadduct are discussed. Products were identified with a combination of NMR spectroscopy, X-ray crystallography, elemental analysis, and (for cycloalkene adducts) reaction with thiophenoxide ion.     

A convenient AIBN-initiated radical addition of ethyl iododifluoroacetate to alkenes

The AIBN-initiated addition of ethyl 4-iodo-2,2-difluoroacetate to a variety of alkene substrates is described. The addition generally led to the corresponding addition products in good to excellent yields and various functional groups could be tolerated under the reaction conditions.     

Solid-phase intermolecular radical reactions 1. Sulfonyl radical addition to isolated alkenes and alkynes

The addition of toluenesulfonyl radicals to solid-supported alkenes and alkynes gives bromo-sulfonyl alkenes and alkanes in good yields.     

Intermolecular radical addition and addition/cyclization reactions of alkoxyamines onto nonactivated alkenes

[reaction: see text] Alkoxyamines A, which are readily prepared from commercially available starting materials, undergo efficient thermal radical carboaminoxylations onto various nonactivated alkenes to provide 1,4-functionalized malonates B in good to excellent yields. The experiments are very easy to conduct. The carboaminoxylations can be combined with radical cyclization and fragmentation processes.     

Iron-catalyzed carbonylation-peroxidation of alkenes with aldehydes and hydroperoxides

A three-component reaction of alkenes, aldehydes, and hydroperoxides catalyzed by FeCl(2) to β-peroxy ketones has been achieved. This three-component reaction can be also applied to the synthesis of α-carbonyl epoxides, through either a stepwise base-induced epoxidation of the separated β-peroxy ketone products or a one-pot process by simply adding base to the reaction mixture after the completion of the three-component reaction.     

Et3B-induced radical addition of N,N-dichlorosulfonamide to alkenes and pyrrolidine formation via radical annulation

A highly regioselective radical addition of N,N-dichlorobenzenesulfonamide (dichloramine-B) to 1-alkenes is achieved at -78 degrees C by the use of triethylborane as a radical initiator. The reaction of 1,3-dienes with N,N-dichlorosulfonamide in the presence of Et(3)B regioselectively provides N-chloro-N-allylamide derivatives. N-chloro-N-allylamides thus obtained react with a variety of alkenes to furnish pyrrolidine derivatives in good yields. A radical annulation reaction among N,N-dichlorosulfonamide, 1,3-dienes, and alkenes has been developed.     

Efficient radical addition of tertiary amines to electron-deficient alkenes using semiconductors as photochemical sensitisers

Tertiary amines can be added to electron-deficient alkenes with yields up to 98% in a radical chain reaction initiated by a photochemical electron transfer using inorganic semiconductors like TiO2 as sensitiser.     

Consecutive approach to alkenes that combines radical addition of phosphorus hydrides with Horner-Wadsworth-Emmons-type reactions

[reaction: see text] Addition of diethyl thiophosphite to terminal alkenes, in the presence of a radical initiator, followed by deprotonation of the phosphonothioate and reaction with a ketone, offers a concise one-pot approach to substituted alkenes. This novel method, which can incorporate alkylation or acylation steps, can be applied to the stereoselective formation of sterically hindered tri- and tetrasubstituted alkenes.     

N-Phenyltriazolinedione as an initiator in the radical addition of thiophenol to alkenes

N-Phenyltriazolinedione is found to be an efficient initiator in the radical (anti-Markovnikov) addition of thiophenol to 2-methyl-2-butene. A second, minor, product (an alcohol, from oxygen addition) was also obtained, and a possible mechanistic scheme is proposed.     

Indium(III) acetate-catalyzed intermolecular radical addition of organic iodides to electron-deficient alkenes

In the presence of phenylsilane and a catalytic amount of indium(III) acetate, organic iodides added to electron-deficient alkenes in ethanol at room temperature. Both simple and functionalized organic iodides were applicable to this reaction. A plausible reaction mechanism involves the formation of indium hydride species by hydride transfer from silicon to indium and an indium hydride-mediated radical chain process.     

Tandem radical addition reactions to substituted indoles under atom-transfer and oxidative conditions

The dimethyl methylmalonyl radical was generated upon photolysis of dimethyl bromomethylmalonate or treatment of dimethyl methylmalonate with Mn(OAc)₃·2 H₂O. This radical was added to an exocyclic olefin appended to 1-acyl or 3-acyl indoles, with subsequent cyclization to generate 1,2- or 2,3- fused indole derivatives, respectively.     

Iron-catalyzed regio- and stereoselective chlorosulfonylation of terminal alkynes with aromatic sulfonyl chlorides

Terminal alkynes react with aromatic sulfonyl chlorides in the presence of an iron(II) catalyst and a phosphine ligand to give (E)-β-chlorovinylsulfones with 100% regio- and stereoselectivity. Various functional groups, such as chloride, bromide, iodide, nitro, ketone, and aldehyde, are tolerated under the reaction conditions. Addition of tosyl chloride to a 1,6-enyne followed by radical 5-exo-trig cyclization gave an exocyclic alkenylsulfone.     

Ag-catalyzed sulfonylation-peroxidation of alkenes with sulfonyl hydrazides and T-hydro

The sulfonylation-peroxidation of alkenes with sulfonyl hydrazides and T-hydro was developed. The Ag-catalyzed three-component peroxidation provides a method for synthesis of a variety of β-sulfonyl peroxides, which could be converted into various sulfone derivatives.     

Decarbonylative radical conjugate addition of aliphatic aldehydes for alkylation of electron-deficient alkenes

A convenient metal-free decarbonylative radical conjugate addition of aliphatic aldehydes to electron-deficient alkenes is developed. With DTBP as an oxidant and radical-initiator, this reaction smoothly converts α-unsubstituted, α-mono-substituted and α-di-substituted aliphatic aldehydes into the corresponding primary, secondary and tertiary alkyl radicals, and subsequently allows for the cascade construction of C(sp³)C(sp³) bond via radical conjugate addition.     

Copper-catalysed intramolecular O-H addition to unactivated alkenes

Intramolecular cyclisation of ω-alkenoic acids and alkenols can be achieved using a catalytic amount of Cu(OTf)₂ to afford lactones and cyclic ethers, offering a practical alternative to existing catalysts.     

Radical addition to isonitriles: a route to polyfunctionalized alkenes through a novel three-component radical cascade reaction

The reaction of aromatic disulfides, alkynes, and isonitriles under photolytic conditions affords polyfunctionalized alkenes--beta-arylthio-substituted acrylamides or acrylonitriles--in fair yields through a novel three-component radical cascade reaction. The procedure entails addition of a sulfanyl radical to the alkyne followed by attack of the resulting vinyl radical to the isonitrile. A fast reaction, e.g., scavenging by a nitro derivative or beta-fragmentation, is necessary in order to trap the final imidoyl radical, since addition of vinyl radicals to isonitriles seems to be a reversible process. The stereochemistry of the reaction is discussed, particularly with respect to the stereochemical outcome of related hydrogen abstraction reactions by the same vinyl radicals. The lower or even inverted preference for either geometrical isomer observed in our cases with respect to that encountered in hydrogen abstraction reactions is explained in terms of transition-state interactions and/or isomerization of the final imidoyl radical. The latter possibility is supported by semiempirical calculations, which show that the spin distribution in the imidoyl radical can allow rotation of the adjacent carbon-carbon double bond prior to beta-fragmentation.     

Rate constants for the addition of the 2-cyano-2-propyl radical to alkenes in solution

Absolute rate constants for the addition of the 2-cyano-2-propyl radical to 26 alkenes CH₂=CXY at 315 K were determined in solution by time-resolved electron-spin-resonance spectroscopy. They vary with the alkene substituents from 30 M^?1 s^?1 to 7′010 M^?1 s^?1. For styrene the temperature dependence is given by log k/M^?1 s^?1 = 7.7 ? 26.1/Θ where Θ = 2.303 RT in kJ/mol. An analysis of the substituent effects in terms of polar and enthalpic factors reveals a dominant influence of the overall reaction enthalpy. © 1993 John Wiley & Sons, Inc.