Effect of molecular structure on mesomorphism XX. Unsymmetrical dimeric mesogens

A series of unsymmetrical dimeric mesogens was prepared, members of which were composed of a 4'-pentyloxybiphenyl-4-carboxyl core and a 4'-substituted-benzylidene-4-oxyaniline core joined via an alklyene spacer. The structural variants were cyano, nitro and trifluoromethyl. Comparison of mesophase behaviour of the unsymmetrical dimers with that of corresponding monomeric 'halves' and also with that of corresponding symmetrical dimers indicated a tendency for the unsymmetrical dimers to form smectic phases although not as highly ordered as those of some of the monomers corresponding to a relevant core group.     

A Novel Reactivity of Phosphanylalumane (>P−Al<): Reversible Addition of a Saturated Interelement Bond to Olefins

The reversible addition of olefins to a phosphanylalumane, P−Al single-bond species, was investigated. The P−Al bond added to ethylene and relatively small terminal alkenes (propylene and hex-1-ene) at room temperature to give the corresponding alkene adducts. Heating the terminal alkene adducts released the corresponding alkenes and regenerated the P−Al bond, but no release of ethylene was observed even under vacuum conditions. The reactivity of ethylene adduct as a new saturated C₂ vicinal P/Al-based FLP was also investigated. The ethylene adduct was found to undergo complexation with nitriles to give the corresponding nitrile adducts to the Al center, which retained the ethylene tether as in the case of the corresponding P/B-based FLP. However, the reactivity of ethylene toward CO₂ and benzaldehyde differed from that of the P/B system giving the corresponding adducts.     

Catalytic oxidation adjacent to carbonyl groups and at benzylic positions with a fluorous seleninic acid in the presence of iodoxybenzene

In conjunction with iodoxybenzene as oxidant, perfluorooctylseleninic acid serves as a catalyst for the oxidation of aryl alkyl ketones to the corresponding ketoacids. Benzylic methylene groups are also oxidized by this reagent combination to the corresponding ketones.     

Comparative theoretical studies on energetic substituted 1,2,4-triazole molecules and their corresponding ionic salts containing 1,2,4-triazole-based cations or anions

We have studied the densities, heats of formation, energetic properties, and thermodynamics of formation for a series of substituted 1,2,4-triazole molecules and their corresponding ionic salts containing 1,2,4-triazolium cations or 1,2,4-triazolide anions using density functional theory and volume-based thermodynamics method. The results show that when the 1,2,4-triazole molecules lose a proton to form corresponding 1,2,4-triazole-based anions, their salts have smaller densities than corresponding molecules. When the molecules get a proton to form the 1,2,4-triazole-based cations, their salts have higher densities than corresponding molecules. The transformation of the 1,2,4-triazole derivatives from nonionic molecules to corresponding cations or anions are very helpful for increasing their heats of formation. Changing the 1,2,4-triazole derivatives into corresponding cations or anions produce different effects on their heats of detonation. Overall, as the compound numbering varies, the evolution trend of heat of detonation is very similar to heat of formation. The salts containing the 1,2,4-triazolide anions have smaller detonation velocities and pressures than corresponding 1,2,4-triazole molecules, whereas the salts containing the 1,2,4-triazolium cations have higher detonation velocities and pressures than corresponding molecules. Finally, the lattice enthalpies and entropies were used to construct a thermodynamic cycle for salt formation to predict the possibility to synthesize the salts.     

Synthesis and thermal stability of benzoxazine nitroxides

A new class of stable nitroxides (aminoxyls) having a 1,4-benzoxazine structure were synthesized and the corresponding thermal stability tested. All derivatives were stable in the entire range of temperatures employed, except those having a benzyl or a tert-butyl group at the β-position with respect to the aminoxyl function, which underwent radical fragmentation. Such a behavior allowed a kinetic study, carried out by means of EPR spectroscopy, to determine the corresponding rate constants and activation parameters (E(a)). Appropriate DFT calculations were performed for all nitroxides including also the thermally stable ones, in order to study the geometries of the fragmentation transition States as well as to compute the corresponding bond dissociation enthalpies (BDH), useful for further modeling purposes. The data obtained were interpreted on the basis of the relative stability of the leaving radical, according to the corresponding E(a) and BDH, whereas in the case of tert-butyl derivatives steric hindrance should play a determinant role, as evidenced by a comparison of the geometric, kinetic, and thermodynamic parameters upon the whole series.     

Stereoselective preparation of functionalized acyclic alkenylmagnesium reagents using i-PrMgCl.LiCl

Acyclic functionalized alkenyl iodides are converted with high stereoselectivity to the corresponding functionalized alkenylmagnesium derivatives by the reaction with i-PrMgCl.LiCl between -40 and -20 degrees C. Functional groups such as a nitrile, chloride, iodide, and ester are readily tolerated. The conversion of an alkenyl iodide bearing a keto group to the corresponding silylated cyanohydrin allows preparation of the corresponding Grignard reagent affording, after acylation and deprotection, unsaturated 1,4-diketones.     

Effect of molecular structure on mesomorphism XX. Unsymmetrical dimeric mesogens

Abstract

A series of unsymmetrical dimeric mesogens was prepared, members of which were composed of a 4′-pentyloxybiphenyl-4-carboxyl core and a 4′-substituted-benzylidene-4-oxyaniline core joined via an alklyene spacer. The structural variants were cyano, nitro and trifluoromethyl. Comparison of mesophase behaviour of the unsymmetrical dimers with that of corresponding monomeric ‘halves’ and also with that of corresponding symmetrical dimers indicated a tendency for the unsymmetrical dimers to form smectic phases although not as highly ordered as those of some of the monomers corresponding to a relevant core group.     

Pd/C-catalyzed Reductive Mono-N-alkylation of Nitrophenol Derivatives in One-pot Way

A range of different nitrophenol derivatives were converted in one‐pot to the corresponding secondary alkyl aminophenols in good to excellent yields by using ketones as alkyl source and hydrogen over 10 wt% Pd/C as reducing agent. In all examples, except for one, the secondary amine was the sole alkylation product isolated. When aldehydes were used as alkyl source, the corresponding tertiary amine as a sole alkylation product was isolated.     

Hofmann rearrangement of primary carboxamides and cyclic imides using DCDMH and application to the synthesis of gabapentin and its potential peptide prodrugs

Two protocols for the efficient transformation of aromatic as well as aliphatic primary carboxamides to the corresponding carbamates and aromatic as well as aliphatic cyclic imides to the corresponding anthranilic acid derivatives & amino acid derivatives, respectively, are described. We also developed a novel methodology to the multigram scale synthesis of gabapentin and (S)-pregabalin. The gabapentin methyl carbamate was converted to novel potential peptide prodrugs of gabapentin.     

Synthesis of tetrahydroisoquinoline (TIQ)–oxazoline ligands and their application in enantioselective Henry reactions

A novel family of eleven new tetrahydroisoquinoline (TIQ)–oxazoline intermediates and five corresponding copper(II) catalysts has been developed and applied to the catalytic asymmetric Henry reaction of various aldehydes with nitromethane to provide β-hydroxy nitroalkanes in high conversion (>99%). This paper describes the synthesis of the TIQ compounds from l-dihydroxyphenylalanine (l-DOPA) as the starting material. The chiral ligands were complexed in situ with various transition metals such as Cu, Sc, Co, Zn, Ni and Mn and tested as a chiral catalyst for the Henry reaction. The reaction was optimized in terms of the metal, counter ion, solvent, temperature and over a range of substrates. The corresponding catalyst with copper(II) acetate and 2-propanol as the solvent provides the best enantioselectivities (up to 77% ee) of the corresponding nitroalcohol for 4-chlorobenzaldehyde.     

Ruthenium- and Copper-Catalyzed Propargylic Substitution Reactions of Propargylic Alcohol Derivatives with Hydrazones

Ruthenium- and copper-catalyzed propargylic substitution reactions of propargylic alcohol derivatives with N-monosubstituted hydrazones as ambident nucleophiles are achieved in which N-monosubstituted hydrazones exhibit impressive different reactivities depending on different catalytic systems, behaving as carbon-centered nucleophiles to give the corresponding propargylic alkylated products in ruthenium catalysis, or as nitrogen-centered nucleophiles to afford the corresponding propargylic aminated products in copper catalysis. DFT calculations were carried out to investigate the detailed reaction pathways of these two systems. Further transformation of propargylic substituted products affords the corresponding multisubstituted pyrazoles as cyclization products in good to high yields.     

Ionic liquids as reagents and solvents in conjunction with microwave heating: rapid synthesis of alkyl halides from alcohols and nitriles from aryl halides

We show that using ionic liquids as reagents in conjunction with microwave heating it is possible to prepare primary alkyl halides from the corresponding alcohols rapidly. Using ionic liquids as solvents in conjunction with microwave heating it is possible to prepare aryl nitriles from the corresponding aryl bromides or iodides. The scope and limitations of using microwave-promotion as a tool in these reactions is discussed.     

Facile synthesis of cyclic α-perfluoroalkyl-α-aminophosphonates

Addition of diethylphosphite to cyclic α-perfluoalkyl substituted imines in the presence of boron trifluoride etherate as a catalyst presents an efficient route for racemic saturated cyclic α-perfluoroalkyl-α-aminophosphonates. Hydrolysis of latter compounds gives the corresponding α-aminoalkanephosphonic acids existing as the corresponding zwitterions according IR and X-ray data.     

Alkynes as synthetic equivalents to stabilized Wittig reagents: intra- and intermolecular carbonyl olefinations catalyzed by Ag(I), BF3, and HBF4

[reaction: see text] The first use of cationic silver (AgSbF4) as a catalyst for intra- and intermolecular alkyne-carbonyl coupling to form conjugated enones is described, and a comparison to corresponding Br?nsted acid (HBF4) and Lewis acid (BF3) catalyst systems is made. Notably, intermolecular coupling proceeds stereoselectively to afford the corresponding trisubstituted enones as single geometrical isomers. This transformation represents a completely atom economical alternative to the use of stabilized Wittig reagents in carbonyl olefination and may be viewed as a formal alkyne-carbonyl metathesis.     

Tin-free radical addition of acyloxymethyl to imines

Acyloxymethyl radicals were generated from the corresponding iodomethyl esters and successfully underwent addition to the CN bond of N-Ts, N-PMP, and N-Dpp imines by the action of dimethylzinc or triethylborane. Ethyl acetate, toluene, and benzene as well as dichloromethane were suitable solvents. The utility of acyloxymethyl radicals as a hydroxymethyl anion equivalent was highlighted by the facile hydrolysis of the acyloxy moiety of the adducts to give the corresponding amino alcohol derivatives in good to high yield.     

Mechanism of meerwein-pondorf-verley type reductions

The reduction of benzophenone by lithium and chloromagnesium alkoxides has been studied as well as the transformation of certain lithium alkoxides to the corresponding ketones by electron transfer. Fluorenone was reduced by lithium sec-butoxide to the corresponding lithium ketyl to the extent of 65%. Lithium 9-fluoroenolate underwent in tetrahydrofuran a spontaneous transformation to lithium fluorenone ketyl. This process was interpreted as involving 1,2-hydrogen shift in an oxygen-centred radical. A mechanism for the Meerwein-Pondorf-Verley-type reductions is proposed, invoking single electron as well as 1,2-hydrogen shift steps.     

钯碳催化下以甲酰肼为还原剂的卤代芳烃还原偶联反应研究

在Pd/C催化下, 以甲酰肼为还原剂, 卤代芳烃通过还原偶联反应能高选择性地合成相应的联苯化合物. 具有不同取代基的卤代芳烃的还原偶联反应产率在52%～94%之间.     

Stereoselective synthesis of 2-dienyl-substituted piperidines using an eta4-dienetricarbonyliron complex as the stereocontrolling element in a double reductive amination cascade

In the presence of NaBH(OAc)(3), a 1,5-keto-aldehyde, contained within a side-chain of an eta(4)-dienetricarbonyliron complex, undergoes a double reductive amination sequence with a series of primary amines, to provide the corresponding piperidine products in good to excellent yield. The dienetricarbonyliron complex functions as a powerful chiral auxiliary in this cascade process, exerting complete control over the stereoselectivity of the reaction, with the formation of a single diastereoisomeric product. The sense of stereoinduction has been confirmed by X-ray crystallography. Removal of the tricarbonyliron moiety can be effected with CuCl(2) to afford the corresponding 2-dienyl-substituted piperidine in excellent yield. Attempted extension of this cyclisation strategy to the corresponding azepane ring system using a 1,6-keto-aldehyde as the cyclisation precursor was unsuccessful; in this case, the reaction stopped after a single reductive amination on the aldehyde to provide an acyclic keto-amine product.     

A convenient method to access long-chain and functionalised mixed methylphosphonate esters and their application in the synthesis of ionic liquids

A new method to synthesise long-chain and functionalised methylphosphonate esters and the corresponding ionic liquids is reported. The synthesis comprises the formation of dialkyl methylphosphonate esters in a S(N)2 reaction followed by the use of these esters as alkylating agents to form the corresponding, new alkyl methylphosphonate ILs.     

One-pot reductive monoalkylation of nitro aryls with hydrogen over Pd/C

A range of different nitro aryls were converted in one-pot to the corresponding secondary alkyl amino aryls in good to excellent yields by using aldehydes as alkyl source and hydrogen over Pd/C (10%) as reducing agent. In all examples, but one, the secondary amine was the sole alkylation product isolated. When formaldehyde was used as the alkyl source, substantial amount of the corresponding tertiary amine was isolated, however, by altering the reaction conditions slightly the corresponding secondary amine could be isolated in superb yield.