Thermal decomposition mechanisms of tert-alkyl peroxypivalates studied by the nitroxide radical trapping technique

The thermolysis of a series of tert-alkyl peroxypivalates 1 in cumene has been investigated by using the nitroxide radical-trapping technique. tert-Alkoxyl radicals generated from the thermolysis underwent the unimolecular reactions, beta-scission, and 1,5-H shift, competing with hydrogen abstraction from cumene. The absolute rate constants for beta-scission of tert-alkoxyl radicals, which vary over 4 orders of magnitude, indicate the vastly different behavior of alkoxyl radicals. However, the radical generation efficiencies of 1 varied only slightly, from 53 (R = Me) to 63% (R = Bu(t)()), supporting a mechanism involving concerted two-bond scission within the solvent cage to generate the tert-butyl radical, CO(2), and an alkoxyl radical. The thermolysis rate constants of tert-alkyl peroxypivalates 1 were influenced by both inductive and steric effects [Taft-Ingold equation, log(rel k(d)) = (0.97 +/- 0. 14)Sigmasigma - (0.31 +/- 0.04)SigmaE(s)(c), was obtained].     

Benzotriazolyl-mediated 1,2-shifts of electron-rich heterocycles

The anion formed from the lithiation of 1-[(methylthio)methyl]-1H-benzotriazole 1 with n-BuLi adds to heteroaryl ketones to give 2-benzotriazolyl alcohols 3a-m. Thermolysis of 3a-g in the presence of zinc bromide induces a 1,2-shift of heteroaromatic groups to form ketones 4a-g. By contrast, in the rearrangement of 2-benzotriazolyl alcohols 3h,i,k-m migration of the phenyl group rather than the corresponding heteroaromatic groups occurred to give ketones 4h,i,k-m.     

Enantioselective hydrocyanation of aldehydes catalyzed by [Li{Ru(phgly)2(binap)}]X (X = Cl, Br)

Novel bimetallic complexes [Li{Ru[(S)-phgly](2)[(S)-binap]}]X (X = Cl, Br) are readily synthesized by mixing Ru[(S)-phgly](2)[(S)-binap] and LiX. A single-crystal X-ray analysis reveals the structure. These bimetallic complexes efficiently catalyze asymmetric hydrocyanation of aldehydes with a substrate-to-catalyst molar ratio of 500-2000 at -78 to -60 °C. A range of aromatic, heteroaromatic, and α,β-unsaturated aldehydes as well as a tert-alkyl aldehyde is converted to the cyanohydrins in high enantiomeric excess (up to 99%).     

Switch in stereoselectivity caused by the isocyanide structure in the rhodium-catalyzed silylimination of alkynes

The reaction of terminal alkynes with hydrosilanes and tert-alkyl isocyanides in the presence of Rh(4)(CO)(12) gives (Z)-β-silyl-α,β-unsaturated imines in good yields. On the other hand, the use of aryl isocyanides in place of tert-alkyl isocyanides leads to the formation of E isomers.     

Highly efficient hydrophosphonylation of aldehydes and unactivated ketones catalyzed by methylene-linked pyrrolyl rare earth metal amido complexes

A series of rare earth metal amido complexes bearing methylene-linked pyrrolyl-amido ligands were prepared through silylamine elimination reactions and displayed high catalytic activities in hydrophosphonylations of aldehydes and unactivated ketones under solvent-free conditions for liquid substrates. Treatment of [(Me(3)Si)(2)N](3)Ln(μ-Cl)Li(THF)(3) with 2-(2,6-Me(2)C(6)H(3)NHCH(2))C(4)H(3)NH (1, 1 equiv) in toluene afforded the corresponding trivalent rare earth metal amides of formula {(μ-η(5):η(1)):η(1)-2-[(2,6-Me(2)C(6)H(3))NCH(2)](C(4)H(3)N)LnN(SiMe(3))(2)}(2) [Ln=Y (2), Nd (3), Sm (4), Dy (5), Yb (6)] in moderate to good yields. All compounds were fully characterized by spectroscopic methods and elemental analyses. The yttrium complex was also characterized by (1)H NMR spectroscopic analyses. The structures of complexes 2, 3, 4, and 6 were determined by single-crystal X-ray analyses. Study of the catalytic activities of the complexes showed that these rare earth metal amido complexes were excellent catalysts for hydrophosphonylations of aldehydes and unactivated ketones. The catalyzed reactions between diethyl phosphite and aldehydes in the presence of the rare earth metal amido complexes (0.1 mol%) afforded the products in high yields (up to 99%) at room temperature in short times of 5 to 10 min. Furthermore, the catalytic addition of diethyl phosphite to unactivated ketones also afforded the products in high yields of up to 99% with employment of low loadings (0.1 to 0.5 mol%) of the rare earth metal amido complexes at room temperature in short times of 20 min. The system works well for a wide range of unactivated aliphatic, aromatic or heteroaromatic ketones, especially for substituted benzophenones, giving the corresponding α-hydroxy diaryl phosphonates in moderate to high yields.     

Asymmetric Catalysis by Architectural and Functional Molecular Engineering: Practical Chemo- and Stereoselective Hydrogenation of Ketones

Hydrogenation is a core technology in chemical synthesis. High rates and selectivities are attainable only by the coordination of structurally well-designed catalysts and suitable reaction conditions. The newly devised [RuCl(2)(phosphane)(2)(1,2-diamine)] complexes are excellent precatalysts for homogeneous hydrogenation of simple ketones which lack any functionality capable of interacting with the metal center. This catalyst system allows for the preferential reduction of a C=O function over a coexisting C=C linkage in a 2-propanol solution containing an alkaline base. The hydrogenation tolerates many substituents including F, Cl, Br, I, CF(3), OCH(3), OCH(2)C(6)H(5), COOCH(CH(3))(2), NO(2), NH(2), and NRCOR as well as various electron-rich and -deficient heterocycles. Furthermore, stereoselectivity is easily controlled by the electronic and steric properties (bulkiness and chirality) of the ligands as well as the reaction conditions. Diastereoselectivities observed in the catalytic hydrogenation of cyclic and acyclic ketones with the standard triphenylphosphane/ethylenediamine combination compare well with the best conventional hydride reductions. The use of appropriate chiral diphosphanes, particularly BINAP compounds, and chiral diamines results in rapid and productive asymmetric hydrogenation of a range of aromatic and heteroaromatic ketones and gives a consistently high enantioselectivity. Certain amino and alkoxy ketones can be used as substrates. Cyclic and acyclic alpha,beta-unsaturated ketones can be converted into chiral allyl alcohols of high enantiomeric purity. Hydrogenation of configurationally labile ketones allows for the dynamic kinetic discrimination of diastereomers, epimers, and enantiomers. This new method shows promise in the practical synthesis of a wide variety of chiral alcohols from achiral and chiral ketone substrates. Its versatility is manifested by the asymmetric synthesis of some biologically significant chiral compounds. The high rate and carbonyl selectivity are based on nonclassical metal-ligand bifunctional catalysis involving an 18-electron amino ruthenium hydride complex and a 16-electron amido ruthenium species.     

Osmium pyme complexes for fast hydrogenation and asymmetric transfer hydrogenation of ketones

The osmium compound trans,cis-[OsCl2(PPh3)2(Pyme)] (1) (Pyme=1-(pyridin-2-yl)methanamine), obtained from [OsCl2(PPh3)3] and Pyme, thermally isomerizes to cis,cis-[OsCl2(PPh3)(2)(Pyme)] (2) in mesitylene at 150 degrees C. Reaction of [OsCl2(PPh3)3] with Ph2P(CH2)(4)PPh2 (dppb) and Pyme in mesitylene (150 degrees C, 4 h) leads to a mixture of trans-[OsCl2(dppb)(Pyme)] (3) and cis-[OsCl2(dppb)(Pyme)] (4) in about an 1:3 molar ratio. The complex trans-[OsCl2(dppb)(Pyet)] (5) (Pyet=2-(pyridin-2-yl)ethanamine) is formed by reaction of [OsCl2(PPh3)3] with dppb and Pyet in toluene at reflux. Compounds 1, 2, 5 and the mixture of isomers 3/4 efficiently catalyze the transfer hydrogenation (TH) of different ketones in refluxing 2-propanol and in the presence of NaOiPr (2.0 mol %). Interestingly, 3/4 has been proven to reduce different ketones (even bulky) by means of TH with a remarkably high turnover frequency (TOF up to 5.7 x 10(5) h(-1)) and at very low loading (0.05-0.001 mol %). The system 3/4 also efficiently catalyzes the hydrogenation of many ketones (H2, 5.0 atm) in ethanol with KOtBu (2.0 mol %) at 70 degrees C (TOF up to 1.5 x 10(4) h(-1)). The in-situ-generated catalysts prepared by the reaction of [OsCl2(PPh3)3] with Josiphos diphosphanes and (+/-)-1-alkyl-substituted Pyme ligands, promote the enantioselective TH of different ketones with 91-96 % ee (ee=enantiomeric excess) and with a TOF of up to 1.9 x 10(4) h(-1) at 60 degrees C.     

Mechanism of asymmetric hydrogenation of ketones catalyzed by BINAP/1,2-diamine-rutheniumII complexes

Asymmetric hydrogenation of acetophenone with trans-RuH(eta(1)-BH(4))[(S)-tolbinap][(S,S)-dpen] (TolBINAP = 2,2'-bis(di-4-tolylphosphino)-1,1'-binaphthyl; DPEN = 1,2-diphenylethylenediamine) in 2-propanol gives (R)-phenylethanol in 82% ee. The reaction proceeds smoothly even at an atmospheric pressure of H(2) at room temperature and is further accelerated by addition of an alkaline base or a strong organic base. Most importantly, the hydrogenation rate is initially increased to a great extent with an increase in base molarity but subsequently decreases. Without a base, the rate is independent of H(2) pressure in the range of 1-16 atm, while in the presence of a base, the reaction is accelerated with increasing H(2) pressure. The extent of enantioselection is unaffected by hydrogen pressure, the presence or absence of base, the kind of base and coexisting metallic or organic cations, the nature of the solvent, or the substrate concentrations. The reaction with H(2)/(CH(3))(2)CHOH proceeds 50 times faster than that with D(2)/(CD(3))(2)CDOD in the absence of base, but the rate differs only by a factor of 2 in the presence of KO-t-C(4)H(9). These findings indicate that dual mechanisms are in operation, both of which are dependent on reaction conditions and involve heterolytic cleavage of H(2) to form a common reactive intermediate. The key [RuH(diphosphine)(diamine)](+) and its solvate complex have been detected by ESI-TOFMS and NMR spectroscopy. The hydrogenation of ketones is proposed to occur via a nonclassical metal-ligand bifunctional mechanism involving a chiral RuH(2)(diphosphine)(diamine), where a hydride on Ru and a proton of the NH(2) ligand are simultaneously transferred to the C=O function via a six-membered pericyclic transition state. The NH(2) unit in the diamine ligand plays a pivotal role in the catalysis. The reaction occurs in the outer coordination sphere of the 18e RuH(2) complex without C=O/metal interaction. The enantiofaces of prochiral aromatic ketones are kinetically differentiated on the molecular surface of the coordinatively saturated chiral RuH(2) intermediate rather than in a coordinatively unsaturated Ru template.     

trans-RuH(eta1-BH4)(binap)(1,2-diamine): a catalyst for asymmetric hydrogenation of simple ketones under base-free conditions

Reaction of a chiral RuCl2(diphosphine)(1,2-diamine) complex and NaBH4 forms trans-RuH(eta1-BH4)(diphosphine)(1,2-diamine) quantitatively. The TolBINAP/DPEN Ru complex has been characterized by single crystal X-ray analysis as well as NMR and IR spectra. The new Ru complexes allow for asymmetric hydrogenation of simple ketones in 2-propanol without an additional strong base. Various base-sensitive ketones are convertible to chiral alcohols in a high enantiomeric purity with a substrate/catalyst ratio of up to 100 000 under mild conditions. Configurationally unstable 2-isopropyl- and 2-methoxycyclohexanone can be kinetically resolved with a high enantiomer discrimination. This procedure overcomes the drawback of an earlier method using RuCl2(diphosphine)(diamine) and an alkaline base, which sometimes causes undesired reactions such as ester exchange, epoxy-ring opening, beta-elimination, and polymerization of ketonic substrates.     

Kinetic investigation of the OH radical and Cl atom initiated degradation of unsaturated ketones at atmospheric pressure and 298 K

Rate coefficients for the reactions of hydroxyl radicals and chlorine atoms with 4-hexen-3-one, 5-hexen-2-one, and 3-penten-2-one have been determined at 298 ± 2 K and atmospheric pressure of air. Rate coefficients for the compounds were determined using a relative kinetic technique with different reference compounds. The experiments were performed in a large photoreactor (480 L) using in situ FTIR spectroscopy to monitor the decay of reactants. From the different measurements the following rate coefficients (in units of cm(3) molecule(-1) s(-1)) have been determined: k(1)(OH + 4-hexen-3-one) = (9.04 ± 2.12) × 10(-11), k(2)(OH + 5-hexen-2-one) = (5.18 ± 1.27) × 10(-11), k(3)(OH + 3-penten-2-one) = (7.22 ± 1.74) × 10(-11), k(4)(Cl + 4-hexen-3-one) = (3.00 ± 0.58) × 10(-10), k(5)(Cl + 5-hexen-2-one) = (3.15 ± 0.50) × 10(-10) and k(6)(Cl + 3-penten-2-one) = (2.53 ± 0.54) × 10(-10). The reactivity of the double bond in alkenes and unsaturated ketones at 298 K toward addition of OH radicals and Cl atoms are compared and discussed. In addition, a correlation between the reactivity of the unsaturated ketones toward OH radicals and the HOMO of the compounds is presented. On the basis of the kinetic measurements, the tropospheric lifetimes of 4-hexen-3-one, 5-hexen-2-one, and 3-penten-2-one with respect to their reaction with hydroxyl radicals are estimated to be between 2 and 3 h.     

Iridium and rhodium complexes with the planar chiral thioether ligands in asymmetric hydrogenation of ketones and imines

Rhodium complexes with the planar chiral phosphinoferrocenyl thioether ligands [Rh(P,SR)(diene)X] (R = Me, Bu^t, Ph, Bn, diene is cyclooctadiene (COD) or norbornadiene (NBD), X = Cl, BF₄) catalyze hydrogenation of ketones, imines, and heteroaromatic compounds; in the case of acetophenone, the enantioselectivity reached 60% ee. Similar iridium complexes demonstrate a good activity in the hydrogenation of imines, the maximal enantioselectivity in the case of N-phenyl-N-(1-phenylethylidene)amine was about 40% ee.     

Mayr electrophilicity predicts the dual Diels-Alder and sigma-adduct formation behaviour of heteroaromatic super-electrophiles

We report on the dual reactivity, i.e. anionic Meisenheimer sigma adduct formation and Diels-Alder adduct formation, of a series of heteroaromatic super-electrophiles, including 4,6-dinitro-benzofuroxan, -N-arylbenzotriazoles (4), -benzothiadiazole and -benzoselenadiazole. Measured pK(a)(H(2)O) values for sigma adduct formation provide a quantitative measure of super-electrophilic reactivity with a satisfactory correlation between the Mayr E electrophilicity parameter and pK(a)(H(2)O): E = -0.662 pK(a)(H(2)O) (or pK(R+) -3.20 (r(2) = 0.987). The most highly electrophilic, pre-eminent super-electrophile is 4,6-dinitrotetrazolopyridine (E = -4.67, pK(a)(H(2)O) = 0.4), which supercedes the reference Meisenheimer super-electrophile, 4,6-dinitrobenzofuroxan (E = -5.06, pK(a) = 3.75), having itself an E value superior by 8 orders of magnitude compared to 1,3,5-trinitrobenzene as the benchmark normal Meisenheimer electrophile (E = -13.19, pK(a)(H(2)O) = 13.43). (For relevant kinetic parameters as well as E and pK(a) values, see .) In a parallel study we have investigated Diels-Alder (normal and inverse electron demand) reactivity of this series of heteroaromatic electrophiles and have shown that Mayr E values are valid predictors of whether DA adducts will form and how rapidly. The observed order of pericyclic reactivity corresponds to E = -8.5 as the demarcation E value, in close agreement with sigma complexation; thus pointing to a common origin for the two processes, i.e. an inverse relationship between the degree of aromaticity of the carbocyclic ring and ease of sigma complexation, or DA reactivity, respectively.     

Microwave-assisted solvent-free synthesis of enantiomerically pure N-(tert-butylsulfinyl)imines

A simple, environmentally friendly, and very efficient procedure for the synthesis of optically pure N-(tert-butylsulfinyl)imines has been developed with microwave-promoted condensation of aldehydes and ketones using (R)-2-methylpropane-2-sulfinamide in the presence of Ti(OEt)(4), under solvent-free conditions. This procedure allows for the preparation of a variety of sulfinyl aldimines with excellent yields and purities in only 10 min, making any further purification of the imines unnecessary. Several sulfinyl ketimines have also been prepared in good yields by extension of the reaction times to 1 h. This methodology has proved to be equally efficient for the synthesis of aromatic, heteroaromatic, and aliphatic N-(tert-butylsulfinyl)imines. Conventional heating has also been shown to be useful to promote these reactions, especially for the synthesis of aldimines.     

Highly regio- and stereoselective ruthenium(II)-catalyzed direct ortho-alkenylation of aromatic and heteroaromatic aldehydes with activated alkenes under open atmosphere

Various aromatic and heteroaromatic aldehydes reacted with activated alkenes in the presence of a catalytic amount of [{RuCl(2)(p-cymene)}(2)], AgSbF(6), and Cu(OAc)(2)·H(2)O to give substituted alkene derivatives in a highly regio- and stereoselective manner. The corresponding alkene derivatives were further converted into unusual four-membered cyclic ketones or a polycyclic isochromanone derivative via a photochemical rearrangement. Notably, the catalytic reaction was conducted under an open atmosphere.     

均相苯乙酮加氢反应研究

合成了一种新的钌膦配合物[RuCl2(Dmpp)2en](Dmpp=4-(2，6-二甲氧吡啶基)二苯基膦，en=乙二胺)，对其结构进行了表征．系统研究了反应温度，氢气压力，底物和催化剂的比例，碱和催化剂的比例等反应条件对[RuCl2(Dmpp)2en]催化的芳香酮加氢反应活性的影响，证明其在苯乙酮加氢反应中具有很好的催化活性．     

Monoalkyl and monoanilide yttrium complexes containing tridentate pyridyl-1-azaallyl dianionic ligands

A series of pyridyl-1-azaallyl ligand precursors (HL1-HL5) were synthesized via condensation of pyridine ketones with anilines. The alkane elimination reactions between Y(CH(2)SiMe(3))(3)(THF)(2) and HL4 or HL5 gave the monoalkyl complexes (L4-H)YCH(2)SiMe(3)(THF) (1) and (L5-H)YCH(2)SiMe(3)(THF) (2) supported by new tridentate pyridyl-1-azaallyl dianionic ligands. The reactions of monoalkyl complexes, 1 and 2, with one equivalent of 2,6-diisopropylaniline produced the corresponding monoanilide complexes, (L4-H)YNHAr(THF) (3) and (L5-H)YNHAr(THF) (4) (Ar = 2,6-((i)Pr)(2)C(6)H(3)), via highly selective protonolysis of the terminal alkyl Y-CH(2)SiMe(3) bond. Complexes 1-4 are active for intramolecular hydroamination of aminoalkenes.     

Reaction of 2-(2-oxo-2-arylethylidene)-2,3-dihydropyrimidine-4(1H)-ones with aldehydes

2-(2-Oxo-2-arylethylidene)-2,3-dihydropyrimidine-4(1H)-ones react with aromatic and heteroaromatic aldehydes to form the unsaturated ketones, whereas in the case of 3- and 4-benzaldehydes the corresponding trans-2-styrylpyrimidine-4(3H)-ones were obtained. A possible mechanism of hydrolytic cleavage of the product of condensation of 2-(2-oxo-2-phenylethylidene)-2,3-dihydropyrimidine-4(1H)-one with paraformaldehyde under acid catalysis and mechanochemical activation has been discussed.     

Asymmetric addition of 1-ethynylcyclohexene to both aromatic and heteroaromatic ketones catalyzed by a chiral Schiff base-zinc complex

The evaluation of a chiral Schiff base ligand in the zinc-catalyzed asymmetric addition of 1-ethynylcyclohexene to both aromatic and heteroaromatic ketones is reported (with up to 83% enantioselectivity and up to 88% isolated yield).     

Ruthenium(II) hydrazone Schiff base complexes: synthesis, spectral study and catalytic applications

Ruthenium(II) hydrazone Schiff base complexes of the type [RuCl(CO)(B)(L)] (were B=PPh(3), AsPh(3) or Py; L=hydrazone Schiff base ligands) were synthesized from the reactions of hydrazone Schiff base ligand (obtained from isonicotinoylhydrazide and different hydroxy aldehydes) with [RuHCl(CO)(EPh(3))(2)(B)] (where E=P or As; B=PPh(3), AsPh(3) or Py) in 1:1 molar ratio. All the new complexes have been characterized by analytical and spectral (FT-IR, electronic, (1)H, (13)C and (31)P NMR) data. They have been tentatively assigned an octahedral structure. The synthesized complexes have exhibited catalytic activity for oxidation of benzyl alcohol to benzaldehyde and cyclohexanol to cyclohexanone in the presence of N-methyl morpholine N-oxide (NMO) as co-oxidant. They were also found to catalyze the transfer hydrogenation of aliphatic and aromatic ketones to alcohols in KOH/Isopropanol.     

Reactions of a platinum(III) dimeric complex with alkynes in water: novel approach to alpha-aminoketone, alpha-iminoketone, and alpha,beta-diimine via ketonyl-Pt(III) dinuclear complexes

Reaction of the platinum(III) dimeric complex [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(NO(3))(2)](NO(3))(2) (1), prepared in situ by the oxidation of the platinum blue complex [Pt(4)(NH(3))(8)((CH(3))(3)CCONH)(4)](NO(3))(5) (2) with Na(2)S(2)O(8), with terminal alkynes CH[triple bond]CR (R = (CH(2))(n)CH(3) (n = 2-5), (CH(2))(n)CH(2)OH (n = 0-2), CH(2)OCH(3), and Ph), in water gave a series of ketonyl-Pt(III) dinuclear complexes [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(CH(2)COR)](NO(3))(3) (3, R = (CH(2))(2)CH(3); 4, R = (CH(2))(3)CH(3); 5, R = (CH(2))(4)CH(3); 6, R = (CH(2))(5)CH(3); 7, R = CH(2)OH; 8, R = CH(2)CH(2)OH; 9, R = (CH(2))(2)CH(2)OH; 10, R = CH(2)OCH(3); 11, R = Ph). Internal alkyne 2-butyne reacted with 1 to form the complex [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(CH(CH(3))COCH(3))](NO(3))(3) (12). These reactions show that Pt(III) reacts with alkynes to give various ketonyl complexes. Coordination of the triple bond to the Pt(III) atom at the axial position, followed by nucleophilic attack of water and hydrogen shift from the enol to keto form, would be the mechanism. The structures of complexes 3.H(2)O, 7.0.5C(3)H(4)O, 9, 10, and 12 have been confirmed by X-ray diffraction analysis. A competitive reaction between equimolar 1-pentyne and 1-pentene toward 1 produced complex 3 and [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(CH(2)CH(OH)CH(2)CH(2)CH(3))](NO(3))(3) (14) at a molar ratio of 9:1, suggesting that alkyne is more reactive than alkene. The ketonyl-Pt(III) dinuclear complexes are susceptible to nucleophiles, such as amines, and the reactions with secondary and tertiary amines give the corresponding alpha-amino-substituted ketones and the reduced Pt(II) complex quantitatively. In the reactions with primary amines, the once formed alpha-amino-substituted ketones were further converted to the iminoketones and diimines. The nucleophilic attack at the ketonyl group of the Pt(III) complexes provides a convenient means for the preparation of alpha-aminoketones, alpha-iminoketones, and diimines from the corresponding alkynes and amines.