Structures of bromo-substituted pyrone-4-carboxylic acids obtained by direct bromination

Ethyl esters of mono- and dibromocomanic acid were obtained by direct bromination, and the corresponding acids were obtained from the esters by acid hydrolysis. The structures of the compounds obtained and of the previously synthesized bromo-substituted comanic acid were established, and it was proved that the attack of bromine is directed to the 5-C and 3-C atoms; attack takes place first at the more nucleophilic 5-C center, after which the 3-C atom undergoes attack.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 901–903, July, 1978.     

非对称环硫乙烷的区域选择性亲核开环反应

环硫乙烷与它的氧类似物环氧乙烷和氮类似物氮杂环丙烷一样,是一类重要的有机合成中间体,在医药和农用化学品工业领域也得到广泛应用。通过开环和异构化反应,还广泛用于制备硫醇和硫醚等含硫化合物。本文总结了常用亲核试剂对非对称环硫乙烷的亲核开环反应及其区域选择性。环硫乙烷的亲核开环反应通常只受空间效应影响,亲核试剂进攻非对称环硫乙烷位阻小的碳原子,对于烯基取代的环硫乙烷有时可以进攻烯基的β碳原子发生SN2’开环反应。强亲核性的亲核试剂容易致使环硫乙烷脱硫生成烯烃,而亲核性相对较弱的亲核试剂容易发生多聚反应生成多硫醚。在Lewis酸存在下,电子效应会对开环反应的区域选择性产生影响,甚至起主导作用。虽然烷基取代环硫乙烷在Lewis酸存在下的开环仍然主要发生在其取代基少的碳原子上(位阻控制),但受电子效应影响,芳基和烯基取代环硫乙烷的亲核开环,其亲核试剂一般倾向于进攻环硫乙烷的芳甲位和烯丙位碳原子(电子效应控制)。     

Organocatalytic asymmetric direct phosphonylation of alpha,beta-unsaturated aldehydes: mechanism, scope, and application in synthesis

The first direct organocatalytic enantioselective phosphonylation of alpha,beta-unsaturated aldehydes with phosphite, in combination with a Br?nsted acid and a nucleophile, is presented. Mechanistic investigations have revealed that the first step in the catalytic process, after the formation of the iminium intermediate, is the addition of phosphite to the beta-carbon atom, leading to the phosphonium ion-enamine intermediate. The rate-determining step for the reaction is the transformation of P(III) to P(V), which occurs via a nucleophilic SN2-type dealkylation, and a screening of various nucleophiles shows that soft nucleophiles in combination with a Br?nsted acid improve the reaction rate and enantioselectivity. The reaction conditions developed show that the use of 2-[bis(3,5-bistrifluoromethylphenyl)trimethylsilanoxymethyl]pyrrolidine as the catalyst and tri-iso-propyl phosphite as the phosphonylation reagent, in the presence of stoichiometric amount of benzoic acid and sodium iodide, gave the beta-phosphonylation of aromatic and aliphatic alpha,beta-unsaturated aldehydes in good yields and enantioselectivities. The products formed by this new reaction have been used for the synthesis of a number of biologically important compounds, such as optically active hydroxyl phosphonate esters, phosphonic acids, and especially glutamic acid and fosmidomycin precursors, of which the two latter are showing important properties for the treatment of central nervous system diseases and as anti-malarial compounds, respectively. DFT calculations have been applied to explain the approach of the phosphite to the reactive carbon atom in the iminium intermediate in order to account for the observed absolute enantioselectivity in the reaction.     

非对称环氧乙烷的区域选择性亲核开环反应

本文总结了常用亲核试剂对非对称环氧乙烷的亲核开环反应及其区域选择性。强亲核性的亲核试剂通常只受空间效应影响,进攻非对称环氧乙烷位阻小的碳原子,对于烯基取代环氧乙烷还可以进攻烯基的β-碳原子发生S_N2'开环反应,其他亲核试剂同时受空间效应和电子效应的影响,对于烷基环氧乙烷通常进攻其取代少的碳原子, 空间效应起主导作用,而对芳基和烯基取代环氧乙烷开环反应通常发生在环氧乙烷芳甲位和烯丙位的碳原子上, 电子效应起主导作用。在质子酸或强Lewis酸存在下,虽然单烷基环氧乙烷的开环仍然发生在其取代少的碳原子上,但对于芳基、烯基和同碳双取代环氧乙烷,亲核开环反应将主要受电子效应控制,一般亲核试剂倾向于进攻环氧乙烷的芳甲位、烯丙位或多取代的碳原子。分子内的亲核开环反应主要受成环时环大小的控制, 成环时的倾向是五元环> 六元环> 七元环。环氧乙烷亲核开环的区域选择性是环氧乙烷和亲核试剂空间效应和电子效应平衡的结果。     

Theoretical evaluation of the substrate-assisted catalysis mechanism for the hydrolysis of phosphate monoester dianions

Quantum chemistry methods coupled with a continuum solvation model have been applied to evaluate the substrate-assisted catalysis (SAC) mechanism recently proposed for the hydrolysis of phosphate monoester dianions. The SAC mechanism, in which a proton from the nucleophile is transferred to a nonbridging phosphoryl oxygen atom of the substrate prior to attack, has been proposed in opposition to the widely accepted mechanism of direct nucleophilic reaction. We have assessed the SAC proposal for the hydrolysis of three representative phosphate monoester dianions (2,4-dinitrophenyl phosphate, phenyl phosphate, and methyl phosphate) by considering the reactivity of the hydroxide ion toward the phosphorus center of the corresponding singly protonated monoesters. The reliability of the calculations was verified by comparing the calculated and the observed values of the activation free energies for the analogous S_N2(P) reactions of F⁻ with the monoanion of the monoester 2,4-dinitrophenyl phosphate and its diester analogue, methyl 2,4-dinitrophenyl phosphate. It was found that the orientation of the phosphate hydrogen atom has important implications with regard to the nature of the transition state. Hard nucleophiles such as OH⁻ and F⁻ can attack the phosphorus atom of a singly protonated phosphate monoester only if the phosphate hydrogen atom is oriented toward the leaving-group oxygen atom. As a result of this proton orientation, the SAC mechanism in solution is characterized by a small Brønsted coefficient value (β_lg=−0.25). This mechanism is unlikely to apply to aryl phosphates, but becomes a likely possibility for alkyl phosphate esters. If oxyanionic nucleophiles of pK_a<11 are involved, as in alkaline phosphatase, then the S_N2(P) reaction may proceed with the phosphate hydrogen atom oriented toward the nucleophile. In this situation, a large negative value of β_lg (−0.95) is predicted for the substrate-assisted catalysis mechanism.     

Reactions of (2-oxo-1-azetidinyl)-thiophthalimides with nucleophiles

Reaction of the title compounds with a variety of oxygen, nitrogen, carbon and sulfur nucleophiles proceeds by direct attack at the sulfur atom to provide novel substituted N-thio-2-azetidinones.     

Heck-mediated synthesis and photochemically induced cyclization of [2-(2-styrylphenyl)ethyl]carbamic acid ethyl esters and 2-styryl-benzoic acid methyl esters: total synthesis of naphtho[2,1f]isoquinolines (2-azachrysenes)

We describe two new closely related total syntheses of naphtho[2,1-f]isoquinolines. The first synthesis consists of a Heck coupling reaction between trifluoromethanesulfonic acid 2-(2-ethoxycarbonylaminoethyl)phenyl esters and styrenes to give [2-(2-styrylphenyl)ethyl]carbamic acid ethyl esters. These compounds cyclize to give (2-phenanthren-1-yl-ethyl)carbamic acid ethyl esters, from which 2-azachrysenes can be obtained in a three-step sequence. The second synthesis includes a new total synthesis of 2-styrylbenzoic acid methyl esters by Heck coupling of methyl o-iodobenzoates to styrenes, followed by the transformation of the resulting benzoic acid derivatives into phenanthrene-1-carboxylic acid methyl esters and then into the target compounds by a six-step sequence including a Bischler-Napieralski cyclization.     

Synthesis of α-amino acids using transition metal catalysis - alkylation of schiff bases derived from α-amimo acid esters (regio,stereo - selectivity)

A general approach to the synthesis of γ,δ-unsaturated α-amino acid esters is described. Schiff bases derived from glycine and alanine esters were alkylated in the presence of palladium or molybdenum catalysts under neutral or basic conditions using allylic carbonates, esters or halides, (20–95% yield). These less stabilized nucleophiles reacted with the η³ allyl species on the side opposite to the palladium and they can be classified as soft nucleophiles. The regioselectivity was studied with various unsymmetrical electrophiles. After hydrolysis, several functionalized α-amino acids of biological interest (enzymes inhibitors) were obtained. Asymmetric palladium allylic alkylation of the benzophenone imine glycine methyl ester using Pd(OAc)₂ + (+)DIOP was achieved with up to 68 % ee ; the enantioselective Pd-promoted alkylation of this new and useful prochiral nucleophile for the synthesis of α-amino acids is one of the highest ee known.     

Addition Reactions of Benzenesulfinic Acid with Glycals and 1,2-Dibromosugars

The addition of benzenesulfinic acid to glycals was investigated under various conditions, and optimized yields of the glycosyl phenylsulfone products were obtained in the presence of tin tetrachloride as a catalyst. Double bond shift (Ferrier rearrangement) occurred in all cases except amicetal, which lacks a substituent at the allylic carbon. Glycosylation of benzenesulfinic acid with 1,2-dibromides was carried out using silver triflate as the promoter, and gave sulfinate esters as products by reaction at oxygen rather than at sulfur. The sulfinate esters were obtained as mixtures of stereoisomers at the stereogenic sulfur atom. Trapping of the sulfinates with carboxylate nucleophiles was observed during attempted oxidation with MCPBA.     

Palladium catalyzed reaction of allylic geminal diacetates with nucleophiles

The influence of ligands on the palladium catalyzed reaction of allylic-1,1-diol diacetate (1) with sodium dimethyl malonate was studied. When PPh₃ was used as the ligand, the malonate anion was found to attack the carbonyl carbon atom, but it would attack the allylic carbon atom while dppe was used as the ligand. The properties of nucleophiles also influence the position of attack. By suitable choice of the nucleophiles and ligands, dialkylated products can be obtained from 1.     

Studies on the polymerization of ethyl acrylate. II. Chain transfer studies

Transfer constants for different solvents representing hydrocarbons, halogenated compounds, alcohols, ketones, acids, and esters were determined in the thermal polymerization of ethyl acrylate at 80°C and they are compared with the available data on methyl acrylate and ethyl methacrylate. It was observed from the values of transfer constants that ethyl acrylate radicals are a little more effective than methyl acrylate or ethyl methacrylate in abstracting hydrogen atom from hydrocarbons and alcohols. In acetic and n-butyric acid media, it has been found, by the aid of endgroup analysis, that the derived solvent radicals from transfer reactions are not too efficient to start a new chain.     

Halbsandwich‐Komplexe von Ruthenium(II), Rhodium(III) und Iridium(III) mit Tripeptidestern aus α‐, β‐ und γ‐Aminosäuren als Liganden. — Peptidsynthese und Cyclisierung zu Cyclotripeptiden am Metallzentrum

Metal Complexes with Biological Important Ligands. CXLII. Half Sandwich Complexes of Ruthenium(II), Rhodium(III), and Iridium(III) with Tripeptide Esters from α‐, β‐, and γ‐Amino Acids as Ligands. — Peptide Synthesis and Cyclization to Cyclotripeptides at Metal Centers Halfsandwich complexes of ruthenium, rhodium and iridium with deprotonated N, N', N"‐tripeptide ester ligands were obtained from chloro bridged compounds and tripeptide methyl esters ( 1—6 ) or by peptide synthesis at a metal centre ( 9—15 ). For the peptide synthesis at the complex (C₆Me₆)Ru coordinated dipeptide methyl esters from glycine and β‐alanine or γ‐amino butyric acid were elongated by an a‐amino acid methylester. The tripeptide ester Ru(η⁶‐C₆Me₆) complexes with chiral amino acid components and an “asymmetric” metal atom are formed with high diastereoselectivity. The tripeptide esters Gly‐Gly‐β‐AlaOMe, Val‐Gly‐β‐AlaOMe and Phe‐Gly‐β‐AlaOMe can be condensated at the (C₆Me₆)Ru complex with sodium methanolate to give triple deprotonated cyclic tripeptides.     

Synthesis, Resolution, and Enantiomeric Purity Assay of 2-n-Butylbutanedioic Acid 4-t-Butyl Esters

Introduction2-Substituted enantiomerically pure succinic acidderivatives have attracted a considerable interest in re-cent years,mainly because of their importance as chiralbuilding blocks and peptidomimetics in the field ofpharmaceutical design[1—3].Mos…     

5-氟尿嘧啶N1-甲酰基氨基酸、短肽的合成及抗肿瘤活性

5-氟尿嘧啶N¹-甲酰氯分别与Gly、Val、Leu、Ile、Phe、Asp和Glu的苄酯反应,制备了7种5-氟尿嘧啶-N¹-甲酰基氨基酸苄酯。氢解后得到了相应的5-氟尿嘧啶N¹-甲酰氨基酸。将其进一步与氨基酸甲酯或二肽甲酯缩合,制备了5-氟尿嘧啶N¹-甲酰基二肽甲酯和三肽甲酯。5-氟尿嘧啶-N¹-甲酰基二肽甲酯也可采用5-氟尿嘧啶-N¹-甲酰氯与二肽甲酯直接反应制备。     

钯催化烯丙基偕二醇二醋酸酯和各种亲核试剂的反应

研究了配体对烯丙基-1,1-偕二醇二醋酸酯(1)在钯配合物催化下和丙二酸酯钠盐反应的影响. 当用PPh3为配位体时, 丙二酸酯碳阴离子进攻在羰基碳上, 当用dppe为配体时, 进攻在烯丙基碳上. 亲核试剂的性质也影响反应进攻的位置. 通过选择适当的亲核试剂和配体可以从1得到二次烷基化的产物.     

Transition metal-catalysed sequences of nucleophilic addition

Summary In presence of nickel or palladium catalysts, nucleophiles can attack vinylcyclopropanes with concomitant ring cleavage. With palladium catalysts in presence of appropriate substituents the terminal carbon atom of the resulting open chain is able to add to two molecules of a conjugated diene giving rise to long-chain unsaturated compounds.     

Silver(I)-catalyzed tandem 1,3-acyloxy migration/Mannich-type addition/elimination of the sulfonyl group of N-sulfonylhydrazone-propargylic esters to 5,6-dihydropyridazin-4-one derivatives

The addition of nucleophiles to C=N bonds offers a highly efficient synthetic strategy for accessing nitrogen-containing molecules.1 Among the well-developed addition reactions, such as the highly efficient Mannich reaction, various C-H bond-activated compounds including carboxylic acid derivatives, nitroalkanes, and terminal alkynes have been applied as nucleophiles to achieve different classes of amines.2 However, employing new nucleophiles without activated C-H bonds, such as internal alkynes and allenic esters are limited when using metal catalysts.3 Herein, we wish to report a new addition of allenic esters to C=N bonds initiated by a silver-catalyzed 1,3-migration of propargylic esters.     

Boron Photochemistry XVI. Base stabilization of dimesitylboryl-containing dyes and related 11B NMR studies

The UV-visible spectral shifts observed from p-dimesitylboryl-containing dyes in alcohol/sodium hydroxide solutions are caused by attack of the base on the boron atom. This attack produces the light-sensitive, tetravalent, “aterd structure. Dyes have been synthesized with 6 methyl groups ortho to the boron. These dyes axe stable to base. The ¹¹B NMR spectra of a number of dyes and model compounds containing the dimesitylborylphenyl moiety reveal evidence of adduct formation in donor solvents. No adduct formation occurs when 5 or 6 methyl groups surround the boron atom.     

Silver(I)‐Catalyzed Tandem 1,3‐Acyloxy Migration/Mannich‐type Addition/Elimination of the Sulfonyl Group of N‐Sulfonylhydrazone‐propargylic Esters to 5,6‐Dihydropyridazin‐4‐one Derivatives

The addition of nucleophiles to C?N bonds offers a highly efficient synthetic strategy for accessing nitrogen‐containing molecules. 1 Among the well‐developed addition reactions, such as the highly efficient Mannich reaction, various C? H bond‐activated compounds including carboxylic acid derivatives, nitroalkanes, and terminal alkynes have been applied as nucleophiles to achieve different classes of amines. 2 However, employing new nucleophiles without activated C? H bonds, such as internal alkynes and allenic esters are limited when using metal catalysts. 3 Herein, we wish to report a new addition of allenic esters to C?N bonds initiated by a silver‐catalyzed 1,3‐migration of propargylic esters.     

Highly Selective Process for Epoxidation of Fatty Acid Methyl Esters with Peroxyacetic Acid

Specific features of the double-stage process in which unsaturated compounds and, in particular, fatty acid methyl esters of vegetable oils are epoxidated with peroxyacetic acid obtained ex situ in aqueous solutions of acetic acid and hydrogen peroxide under catalysis with Amberlyst 15 Dry ion-exchange resin were examined. It was shown that the independently occurring processes in which the peroxy acid is heterogeneously catalytically formed and epoxy compounds are synthesized can substantially raise the formation selectivity of epoxides with respect to double bonds in fatty acid methyl esters and simplify the simulation of these processes and their technological implementation.