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Isoenriched poly-3-hydroxybutyrate (P3HB) is a biodegradable material with properties similar to isotactic polypropylene, yet efficient routes to this material are lacking after 50+ years of extensive efforts in catalyst design. In this contribution, a novel lanthanum aminobisphenolate catalyst (1-La) can access isoenriched P3HB through the stereospecific ring-opening polymerization (ROP) of rac-β-butyrolactone (rac-BBL). Replacing the tethered donor group of a privileged supporting ligand with a non-coordinating benzyl substituent generates a catalyst whose reactivity and selectivity can be tuned with inexpensive achiral neutral donor ligands (e.g. phosphine oxides, OPR3). The 1-La/OPR3 (R = n-octyl, Ph) systems display high activity and are the most isoselective homogeneous catalysts for the ROP of rac-BBL to date (0 °C: Pm = 0.8, TOF ～190 h-1). Combined reactivity and spectroscopic studies provide insight into the active catalyst structure and ROP mechanism. Both 1-La(TPPO)2 and a structurally related catalyst with a tethered donor group (2-Y) operate under chain-end stereocontrol; however, 2-RE favors formation of P3HB with opposite tacticity (syndioenriched) and its ROP activity and selectivity are totally unaffected by added neutral donor ligands. Our studies uncover new roles for neutral donor ligands in stereospecific ROP, including suppression of chain-scission events, and point to new opportunities for catalyst design. This journal is

The oxidative esterification of various aldehydes with alcohols could be achieved by a heterogeneous iron(iii) catalyst supported on a ring-like POM inorganic ligand under mild conditions, affording the corresponding esters, including several drug molecules and natural products, in high yields. ESI-MS and control experiments demonstrated that POM-FeV(O) was the active catalytic species and the plausible mechanism was presented. More importantly, the 6th run of the iron catalyst recycles shows only a slight decrease in the yield.

Starting from common monounsaturated fatty acids, a strategy is revealed that provides ultra-long aliphatic α,ω-difunctional building blocks by a sequence of two scalable catalytic steps that virtually double the chain length of the starting materials. The central double bond of the α,ω-dicarboxylic fatty acid self-metathesis products is shifted selectively to the statistically much-disfavored α,β-position in a catalytic dynamic isomerizing crystallization approach. “Chain doubling” by a subsequent catalytic olefin metathesis step, which overcomes the low reactivity of this substrates by using waste internal olefins as recyclable co-reagents, yields ultra-long-chain α,ω-difunctional building blocks of a precise chain length, as demonstrated up to a C48 chain. The unique nature of these structures is reflected by unrivaled melting points (Tm=120 °C) of aliphatic polyesters generated from these telechelic monomers, and by their self-assembly to polyethylene-like single crystals.

A new series of palladium catalysts ligated by a chelating bisphosphine monoxide bearing diarylphosphino groups (aryl-BPMO) exhibits markedly higher reactivity for ethylene/methyl acrylate copolymerisation when compared to the first generation of alkyl-BPMO-palladium catalysts that contain a dialkylphosphino moiety. Mechanistic studies suggest that the origin of this disparate catalyst behavior is a change in regioselectivity of migratory insertion of the acrylate comonomer as a function of the phosphine substituents. The best aryl-BPMO-palladium catalysts for these copolymerisations were shown to undergo exclusively 2,1-insertion, and this high regioselectivity avoids formation of a poorly reactive palladacycle intermediate. Furthermore, the aryl-BPMO-palladium catalysts can copolymerise ethylene with other industrially important polar monomers.

The regioselective and diastereoselective chromium(II)-mediated reactions of 4-bromocrotonic acid or amides with aldehydes and ketones can proceed without the need to protect protic sites to generate the respective α-alkenyl-β-hydroxy adducts, i.e. formally the addition of the α-anion of a carboxylic acid or amide to an oxo-compound is featured.

A commercial Pd catalyst based on Sibunit carbon support was treated with H6TeO6 in a reducing media to obtain a Te coating on the surface of Pd particles. The PdTe/C catalyst prepared in this way showed the ability to control the radical chain oxidation of 1,3-butadiene by promoting the selective formation of 2-butene-1,4-diol, 4-hydroxybut-2-enal and furan in DMA (total selectivity of 61% and yield of 7%). At the same time, the catalyst induced oxidation of 1,3-butadiene by a non-radical heterolytic mechanism involving the formation of two groups of primary products: (1) crotonaldehyde and methyl vinyl ketone and (2) the products of oxygenation at the 1,4-positions. The compounds of the second group including 1,4-dimethoxy-2-butene and maleic acid dimethyl ester were formed on PdTe centers in MeOH. Increasing the Te concentration in the PdTe/C catalyst forced the conversion of 1,3-butadiene toward 1,4-oxygenation and simultaneously decreased the intensity of secondary oxidation, resulting in the selective formation of derivatives of the 1,4-oxygenation - 1,4-dimethoxy-2-butene and allenic alcohol methyl ether (total selectivity of 84% and yield of 48%).

Ring opening of various nickela- and palladalactones induced by the cleavage of the M-O bond by methyl trifluoromethanesulfonate (MeOTf) and methyl iodide (MeI) is examined. Experimental evidence supports the mechanism of ring opening by the alkylating agent followed by β-H elimination leading to methyl acrylate and a metal-hydride species. MeOTf shows by far higher efficiency in the lactone ring opening than any other methylating agent including the previously reported methyl iodide.

An atom economic and catalytic substitution reaction of π-activated alcohols by a multimetallic IreSn3 complex has been demonstrated. The multimetallic IreSn3 complex can be easily synthesized from the reaction between [Cp*IrCl2]2 and SnCl2. In presence of as little as 1 mol % of the catalyst three different types of π-activated alcohols, namely benzyl, allyl, and propargyl alcohols, have been successfully transformed into alkylated products using carbon (arenes, heteroarenes, allyltrimethylsilane, and 1,3-dicarbonyls), nitrogen (sulfonamides), oxygen (alcohols), and sulfur (thiols) nucleophiles in very high yields. An electrophilic mechanism is proposed from the Hammett correlation study.

The functionalization of silica gel was carried out using 3-aminopropyltriethoxysilane as a reactive surface modifier followed by covalent grafting of novel tetrakis-(2-methoxy-4-formylphenoxy)phthalocyaninato manganese(III) acetate complex. The resulting inorganic-organic hybrid material was found to be a highly selective and recyclable catalyst for the single-step synthesis of esters. The catalyst was characterized by elemental analysis (CHN), diffuse reflectance UV-visible, 13C CPMAS and 29Si CPMAS NMR spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), BET surface area analysis, energy dispersive X-ray fluorescence (ED-XRF), Fourier-transform infrared (FT-IR) and atomic absorption spectroscopy (AAS) techniques, which demonstrates the covalent grafting of the complex onto functionalized silica gel. The catalytic performance of the novel inorganic-organic hybrid catalyst was evaluated in the direct oxidative esterification of aldehydes with alcohols, at ambient temperature, using hydrogen peroxide as an environment friendly oxidant. The hybrid catalyst presented up to 100% of substrate conversion with high turn-over numbers (TONs), up to 100% of selectivity toward the ester product, and can be recovered and reused for multiple cycles without appreciable loss in its catalytic activity.

Practical and simple catalytic enantioselective hydrogenation reactions to synthesize N-unprotected β-amino esters have been developed: (1) asymmetric hydrogenation of N-unprotected β-enamine ester and (2) asymmetric direct reductive amination of β-keto esters using ammonium salts. A Ru-DM-SEGPHOS complex was used as the catalyst in both cases and gave high enantioselectivity, high reactivity, and wide substrate applicability. These protocols greatly reduced reaction time and waste compared to conventional synthetic routes. The direct reductive amination route was demonstrated on a >100 kg scale.

Systematic studies have been performed to develop highly efficient catalysts for the asymmetric aza-Claisen rearrangement of trihaloacetimidates. Herein, we describe the stepwise development of these catalyst systems involving four different catalyst generations finally resulting in the development of a planar chiral pentaphenylferrocenyl oxazoline palladacycle. This complex is more reactive and has a broader substrate tolerance than all previously known catalyst systems for asymmetric aza-Claisen rearrange-ments. Our investigations also reveal that subtle changes can have a big impact on the activity. With the enhanced catalyst activity, the asymmetric aza-Claisen rearrangement has a very broad scope: the methodology not only allows the formation of highly enantioenriched primary allylic amines, but also secondary and tertiary amines; al-lylic amines with N-substituted quaternary stereocenters are conveniently accessible as well. The reaction conditions tolerate many important functional groups, thus providing stereoselective access to valuable functionalized building blocks, for example, for the synthesis of unnatural amino acids. Our results suggest that face-selective olefin coordination is the enantioselectivitydetermining step, which is almost exclusively controlled by the element of planar chirality.

Facile oxidative transformation of alcohols, aldehydes, and acetal into esters has been demonstrated using bifunctional catalyst of gold supported nanocrystalline β-Ga2O3. The study used alcoholic gel-precipitation method to prepare nanocrystalline support and X-ray diffraction (XRD) to characterize the diffraction features of synthesized nanocrystalline support. The study observed that the Au/β-Ga 2O3 catalyst can be reused after aerobic oxidation with maintaining catalytic activity and selectivity for oxidative esterification. The study also observed that aromatic and aliphatic primary alcohols can be converted into their methyl, ethyl, or propyl esters with high selectivities. The study also found that the esters produced after esterification were in good yields.

Treatment of some aromatic and three dicarboxylic acids with methanol in the presence of beef pancreas lipase (Bpl) results in excellent yields of corresponding esters. The esterification is regiospecific to aromatic ring connected carboxylic functionalities.

N,N′-Diiodo-N,N′-1,2-ethanediylbis(p-toluenesulfonamide) (NIBTS) can be used for the oxidation of aldehydes to the corresponding methyl esters with high efficiency in a single step.

A palladium-phosphine catalytic system modified with nitrogen-containing ligands was examined. The system allows the carbomethoxylation of the methylacetylene-allene fraction yielding methyl methacrylate.

A systematic study on the Horner-Wadsworth-Emmons (HWE) reaction has shown that ethyl diphenylphosphonoacetate and methyl diphenylphosphonoacetate give a high excess of (Z)-alkenes. These reaction conditions were then used to prepare (Z)-ethyl-5-phenylpent-2-enoate, the corresponding (E)-isomer being prepared by standard Wittig chemistry. Reduction of each allylic ester, with diisobutylaluminium hydride (DIBAL), gave the allylic alcohols (15) and (19), respectively. Epoxidation of (15) and (19), under Sharpless conditions, gave separate samples of all four stereoisomers of 2,3-epoxy-5-phenylpentan-1-ol. Esterification of each isomer with Cbz-valine, under Mitsunobu conditions, provided (9)-(12) which were assayed against HIV protease. The cis series (9)-(10) proved to be significantly more potent than the trans (11)-12) and, within each of these series, the isomers derived from L-diisopropyltartrate [(9) and (11)] were the most active.

Ultraviolet photolysis of stoichiometric amounts of methyl oleate and Fe(CO)5 in hexanes solvent at 0°C gives Fe(CO)3(η4-α,β-ester) in which the α,β-unsaturated ester isomer of methyl oleate is stabilized by η4-oxadiene π coordination of the olefin and ester carbonyl groups to the Fe(CO)3 unit. Treatment of the Fe(CO)3(η4-α,β-ester) with pyridine or CO liberates the free α,β-ester, methyl octadec-trans-2-enoate, in 70% yield. The Fe(CO)3 unit both catalyzes the olefin isomerization and stabilizes the α,β-unsaturated ester, which results in the formation of the α,β-ester in a yield far above that (3.5%) observed for simple catalyzed methyl oleate isomerization. The much smaller olefin esters, methyl 3-butenoate and ethyl 4-methyl-4-pentenoate, are isomerized under the same conditions to their α,β-unsaturated esters in 94 and 90% yields, respectively. The effects of reaction conditions on the yield, the use of Fe(CO)3(cis-cyclooctene)2 as a nonphotolytic catalyst, and the mechanism of this useful synthetic process are discussed.

Unlike bimolecular reaction with alcohols, reactions of crotonoyl chloride with equimolar amounts of phenols in toluene follow the third-order kinetics and are of the second order with respect to the phenol.The effect of substituents in the phenyl ring does not obey the Hammett equation.In competitive reaction of crotonoyl chloride with equimolar amounts of phenol and an alcohol, the reaction with less acidic alcohol prevails.

The mechanism of the reaction of β-lactones (2-oxetanones) with potassium alkoxides in aprotic solvents was investigated.Despite previous suggestions, the attack of alkoxide ion occurs on the carbonyl carbon atom of β-lactones, cleaving the acyl-oxygen bond to yield the corresponding potassium alcoholate of the respective β-hydroxycarboxylic acid ester.Next, the unsaturated ester is formed due to potassium hydroxide elimination.The nature of the alkoxide used and complexation of alkali metal cation by crown ether have no significant effect on the reaction course in aprotic solvents.

The elimination kinetics of 3-(methoxycarbonyl)propyl methanesulfonate have been determined in a static system over the temperature range of 289.3-329.8 deg C and pressure range of 43-111 torr.The reaction, in vessels seasoned with allyl bromide and in the presence of at least an equal amount of the free radical suppressor toluene, is homogeneous, unimolecular and first-order kinetically.The rate coefficients follow the Arrhenius equation: log k1 = (13.50 +/- 0.47) - (182.2 +/- 5.3) (2.303 RT)-1.A very high extent of lactone formation suggests an unequivocal participation of the carbonyl oxygen of the CO2CH3 group.The partial rates for the parallel elimination towards the formation of butyrolactone and a small amount of methylbut-3-enoate have been estimated, reported, and discussed.The present results provide further evidence of intimate ion pair mechanisms in the gas phase pyrolyses of special types of organic molecules.

A facile method has been developed for the esterification of halides/alcohols/olefins with carboxylic acids using iron(III) perchlorate.

The effects of inorganic base on the yield and selectivity of carbonylation of 1,4-di(chloromethyl)benzene and allyl chloride, catalyzed by dicobalt octacarbonyl, in methanol with carbon monoxide at atmospheric pressure have been examined.The highest yields of products were obtained with K2CO3 and Na2CO3.Addition of MeI results in a considerable increase in yields in the presence of calcium bases, givimg dimethyl 1,4-phenylenediacetate, which in the absence of MeI is formed in appreciable amounts only in the presence of sodium carbonate.

Tertiary α-carbomethoxy-α,α-dimethyl-methyl cations a have been generated by electron impact induced fragmentation from the appropriately α-substituted methyl isobutyrates 1-4.The destabilized carbenium ions a can be distinguished from their more stable isomers protonated methyl methacrylate c and protonated methyl crotonate d by MIKE and CA spectra.The loss of I. and Br. from the molecular ions of 1 and 2, respectively, predominantly gives rise to the destabilized ions a, whereas loss of Cl. from +. results in a mixture of ions a and c.The loss of CH3. from +. favours skeletal rearrangement leading to ions d.The characteristic reactions of the destabilized ions a are the loss of CO and elimination of methanol.The loss of CO is associated by a very large KER and non-statistical kinetic energy release (T50 = 920 meV).Specific deuterium labelling experiments indicate that the α-carbomethoxy-α,α-dimethyl-methyl cations a rearrange via a 1,4-H shift into the carbonyl protonated methyl methacrylate c and eventually into the alkyl-O protonated methyl methacrylate before the loss of methanol.The hydrogen rearrangements exhibit a deuterium isotope effect indicating substantial energy barriers between the + isomers.Thus the destabilized carbenium ion a exists as a kinetically stable species within a potential energy well.

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The kinetics of the pyrolyses of two bromo esters have been investigated in a static system over the temperature range 379-419 deg C and pressure range 51-110 Torr.The reactions in seasoned vessels, and under maximum inhibition with the radical chain suppressor propene, are homogeneous, unimolecular, and follow a first-order rate law.The Arrhenius equations for these elimination processes were found to be as follows: for methyl 4-bromobutyrate, log k1 (s-1) = (13.38 +/- 0.59) - (216.7 +/- 7.6)kJ mol-1 (2.303RT)-1; for methyl 5-bromovalerate, log k1 (s-1) = (13.83 +/- 0.17) - (228.9 +/- 2.3) kJ mol-1 (2.303RT)-1.The anchimeric assistante of the carbomethoxy substituent is determinant in the elimination process, where dehydrobromination product and lactone formation result from an intimate ion pair type of mechanism.The partial rates toward each of the primary products have been determined, reported, and discussed.The present work provides further support of the intimate ion pair mechanism in the gas-phase pyrolysis of special types of organic halides.

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The kinetics of the gas-phase pyrolysis of several secondary chlorides were determined in a static system over the temperature range 369.9-490.1 deg C and the pressure range of 28-298 Torr.The reactions in seasoned vessels, with the free radical suppressor propene and/or toluene always present, are homogeneous and unimolecular and obey a first-order rate law.The observed rate coefficients are represented by the following Arrhenius equations: for 2-chloropropionitrile, log k1 (s-1) = (13.45+/-0.57)-(236.1+/-8.2) kJ mol-1; for methyl 2-chloropropionate, log k1 (s-1) = (12.22+/-0.54) - (217.0+/-7.4) kJ mol-1 (2.303RT)-1; for methyl 3-chlorobutyrate, log k-1 (s-1) = (13.65 +/-0.39)-(214.9+/-5.0) kJ mol-1 (2.303RT)-1.The data of this work together with those reported in the literature confirm previous correlations that α-alkyl substituents of ethyl chloride give a good straight line, when log k/k0 vs. ?* values (ρ* = -3.58 +/- 0.24, correlation coefficient = 0.996, and intercept = -0.0066 at 360 deg C) are plotted, while α-polar substituents give rise to an inflection point at ?*(CH3) = 0.00 into another straight line (ρ* = -0.46+/-0.06, correlation coefficient = 0.972, and intercept = 0.017 at 360 deg C).Several other polar α-substituents have been found to enhance the dehydrochlorination process by means of their electron delocalization or resonance effect.Revising a work reported on the pyrolysis kinetics of pinacolyl chloride, a Wagner-Meerwein rearrangement appears to be a reasonable explanation for the formation of about 12percent of the 2,3-dimethylbutene products.

The effects of Lewis and Broensted acids upon the photoisomerization reactions of several conjugated butenoic and dienoic esters have been investigated.Lewis acid inhibit the photochemical deconjugation of α,β- to β,γ-unsaturated butenoic esters and shift the photoequilibrium between E and Z isomers toward the Z isomer.As such, irradiation of E α,β-unsaturated esters in the presence of EtAlCl2 provides a convenient method for the preparation of the thermodynamically less stable Z isomer.Irradiation of methyl (E,E)-2,4-hexadienoate and methyl (E,E)-5-phenyl-2,4-pentadienoate in the absence of added catalysts results in nonselective E,Z isomerization to give mixtures of all four stereoisomers in roughly comparable yields.In the presence of the Broensted acid trifluoroacetic acid, quantitative conversion of methyl 2,4-hexadienoates to methyl 3,4-hexadienoate is observed.The acid serves as a catalyst for the thermal 1,3-hydrogen shift of an allenic enol ester formed via a photochemical 1,5-hydrogen shift of the conjugated esters.Irradiation of the ground-state complexes of the conjugated esters with the Lewis acids EtAlCl2 or BF3 results in selective E,Z isomerization about the α,β-double bond in methyl 2,4-hexadienoate and the γ,δ-double bond in methyl 5-phenyl-2,4-pentadienoate.The mechanistic bases for the observed effects of Lewis acids are selective excitation of the more strongly absorbing E complex and more efficient isomerization of the excited E vs.Z complex.

Cathodic methods for the esterification of carboxylic acids and the etherification of phenol and benzenethiol under mild conditions were developed.The esterification was successfully carried out at room temperature by the reaction of alkylating reagents with cathodically-generated quaternary ammonium carboxylates.The etherification was similarly achieved using electrogenerated quaternary ammonium phenolate and halonitrobenzenes.A hindered phenolate anion cathodically-generated from 2,6-di-t-butyl-p-cresol remarkably promoted aldol condensation of aromatic ketones and aldehydes, and allowed subsequent Michael reaction to provide efficiently symmetrical 1,5-diketones.

An investigation of the base-catalyzed conjugative isomerization of a series of β,γ-unsaturated esters to their corresponding α,β-unsaturated esters was performed.It was found that, withh sodium hydride in THF, methyl 3-butenoate isomerized initially to a 5:1 ratio of (Z)- to (E)-methyl 2-butenoates; the Z:E ratio is time dependent, and after several days, the thermodynamic ratio 1:23 = Z:E was obtained.The isomerization appears to be catalytic in NaH, as it proceeds with less than 1 molar equiv of base, no hydrogen evolution is observed, and the reaction rate is approximately first order in NaH and zero order in ester.Under the same conditions (Z)-methyl 3-hexenoate isomerized stereoselectively to (E)-methyl 2-hexenoate while (E)-methyl 3-hexenoate isomerized to a 2:1 mixture of (Z)- and (E)-methyl 2-hexenoates.These product ratios are far from the isomeric compositions obtained under equilibrating conditions.To investigate further the stereochemical outcome of these isomerizations, three isomeric β,γ-unsaturated methyl esters were studied: (a) methyl 3-ethyl-3-butenoate isomerized exlusively to (E)-methyl 3-methyl-2-pentenoate; (b) (E)-methyl 3-methyl-3-pentenoate isomerized exlusively to (Z)-methyl 3-methyl-2-pentenoate; (c) (Z)-methyl 3-methyl-3-pentenoate isomerized exlusively to (E)-methyl 3-methyl-2-pentenoate.In the latter three cases, dimerization was not observed presumably due to steric effects.Related results were observed for a smaller series of β,γ-unsaturated amide isomerizations.Examination of the literature on olefin isomerizations reveals a general trend that the current results exemplify.Thus, in the absence of severe steric factors or cation-anion complexation, deprotonation at allylic positions kinetically preferentially forms the anion possessing a cisoid crotyl subunit (if available) regardless of initial substrate conformation.The stereochemical consequences of this results in E Z and Z E geometry conversions in kinetic 1,2-transpositions of olefins.This generalization can also be applied to the stereochemical results of ketone, ester, and hydrazone enolate formation, base-catalyzed exchange in polysubstituted aromatics and heteroaromatics, and other reactions involving the formation of allylic or benzylic anions.

Reactions of sodium methoxide with five chlorooxiranes (1, 3, 11, 18, and 19) and with the corresponding isomeric chlorocarbonyl compounds have been examined.In two cases the chlorooxirane and the corresponding chlorocarbonyl compound afforded the same products, however, in different yields.In the other cases the chlorooxiranes and the corresponding chlorocarbonyl compounds gave different products.It is concluded that chlorocarbonyl compounds are not formed to a large extent as intermediates.In the reactions of two chlorooxiranes (18 and 19) with sodium methoxide, acetylenic and allenic epoxides may be invoked as transient intermediates.

Carboxylic acids in absolute alcohols, on treatment with thionyl chloride at room temperature give good yields of corresponding esters.

The reactions of three electrophilic radicals, benzoyloxy, and t-butoxy, have been examined with a series of α,β-unsaturated esters; methyl acrylate, methyl methacrylate, and methyl crotonate.For the three monomers the ratio of hydrogen abstraction to double bond addition was found to increase and the ratio of head against tail addition to decrease in the series: benzoyloxy; phenyl; t-butoxy.Relative rates for these reactions have been determined and the factors influencing the mode of reaction are discussed.

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Mixed phosphorus esters obtained from alkanols and phosphorus pentoxide furnish the corresponding esters in 80-90percent yield when refluxed with maleanilic and fumaranilic acids.