Reactivity of indolizines in organic synthesis

This review reports the reactivity of indolizines. The reactions section covers, in general, electrophilic, oxidation, reduction, addition, cycloaddition, condensation, and Mannich and multicomponent reactions. The synthesis of bis-indolizines and cyclazines are reported. The reaction mechanisms are discussed.     

Ruthenium(II) carbonyl complexes of dehydroacetic acid thiosemicarbazone: Synthesis, structure, light emission and biological activity

The reaction of [RuHCl(CO)(B)(EPh₃)₂] (where E = As, B = AsPh₃; E = P, B = PPh₃, py, pip, or mor) and dehydroacetic acid thiosemicarbazone (abbreviated as H₂dhatsc where H₂ stands for the two dissociable protons) in benzene under reflux afford a series of new ruthenium(II) carbonyl complexes containing dehydroacetic acid thiosemicarbazone of general formula [Ru(dhatsc)(CO)(B)(EPh₃)] (where E = As, B = AsPh₃; E = P, B = PPh₃, py, pip or mor; dhatsc = dibasic tridentate dehydroacetic acid thiosemicarbazone). All the complexes have been characterized by elemental analyses, FT-IR, UV-Vis, and ¹H NMR spectral methods. The thiosemicarbazone of dehydroacetic acid behaves as dianionic tridentate O, N, S donor and coordinates to ruthenium via phenolic oxygen of dehydroacetic acid, the imine nitrogen of thiosemicarbazone and thiol sulfur. In chloroform solution, all the complexes exhibit metal-to-ligand charge transfer transitions (MLCT). The crystal structure of one of the complexes [Ru(dhatsc)(CO)(PPh₃)₂] (1) has been determined by single crystal X-ray diffraction which reveals the presence of a distorted octahedral geometry in the complexes. All the complexes exhibit an irreversible oxidation (Ru^III/Ru^II) in the range 0.76-0.89 V and an irreversible reduction (Ru^II/Ru^I) in the range −0.87 to −0.97 V. Further, the free ligand and its ruthenium complexes have been screened for their antibacterial and antifungal activities. The complexes show better activity in inhibiting the growth of bacteria Staphylococcus aureus and Escherichia coli and fungus Candida albicans and Aspergillus niger. These results made it desirable to delineate a comparison between free ligand and its ruthenium complexes.     

A multicomponent synthesis of gem-(β-dicarbonyl)arylmethanes

The reaction of aldehydes with β-dicarbonyls and electron-rich aromatics was investigated to generate in a multicomponent fashion crossed adducts of biological relevance. 4-Hydroxycoumarin, triacetic acid lactone, indole, and a selection of aliphatic and aromatic aldehydes representative of various electronic and steric conditions were employed. The reaction showed a surprising dependence on the solvent, with 1:1 chloroform–water giving the best yield of heterodimeric adducts. The mechanistic rationale for the formation of hetero- rather than homodimeric adducts is discussed.     

Synthesis,crystal structure and biological activities of dehydroacetic acid complexes of Ru(II) and Ru(III) containing PPh3/AsPh3

A series of Ru(II) and Ru(III) complexes of the types [RuX(CO)(EPh₃)₂L] (X = H, E = P; X = Cl, E = P or As) and [RuX₂(EPh₃)₂L] (X = Cl, E = P or As; X = Br, E = As, L = monoanion of dehydroacetic acid) have been synthesized in order to explore their biological activities, such as DNA-binding and antibacterial activity. The complexes were characterized by analytical and spectroscopic techniques. The crystal and molecular structure of [RuCl₂(AsPh₃)₂(L)] has been determined by single crystal XRD. The cyclic voltammograms of the complexes in acetonitrile displayed either quasi-reversible or irreversible redox couples based on the metal centre. The ligand, dehydroacetic acid (DHA) and its metal complexes were tested against five pathogenic bacteria. Absorption titration and cyclic voltammetric studies revealed that the complexes interact with Herring Sperm ds DNA through different binding modes to different extents.     

l-Ascorbic acid in organic synthesis: DBU-catalysed one-pot synthesis of tetramic acid derivatives from 5,6-O-isopropylidene ascorbic acid

Reaction of 5,6-O-isopropylidene-2,3-bis-O-alkyl ascorbic acid with different amines in the presence of DBU at ambient temperature resulted in the formation of 3,4-bis-O-alkyl-1-alkyl-5-(2-hydroxy ethyl)-5-hydroxy-1,5-dihydropyrrol-2-ones in moderate yields.     

Unexpected Knoevenagel self-condensation reaction of tetronic acid: synthesis of a new class of organic heterocyclic salts

A new class of pyridinium, quinolinium, isoquinolinum, and N-methylimidazolium-3-(2,5-dihydro-5-oxofuran-3-yl)-4-hydroxyfuran-2(5H)-one salts have been prepared in high yields by reacting pyridine, quinoline, isoquinoline, N-methylimidazole, 1,4-diazabicyclo[2.2.2]octane, and their derivatives with tetronic acid in CH₂Cl₂.     

脱氢醋酸与氨的反应

脱氢醋酸(1)与氨反应生成2,6-二甲基-4-羟基吡啶(2)^[1]。IguChi等^[2]曾用纸层析法定性地研究了这反应的过程。为进一步了解(1)与氨反应的历程及影响反应的因素,我们用HPLC研究了在不同反应条件下得到的中间体和产物,研究了相互转变关系,并进行了分离和鉴定。初步提出了该反应的可能历程。     

Reactivity of thiophosphinous acid bound to ruthenium

The thiophosphinous acid coordinated to ruthenium through the phosphorus atom in [CpRu(PPh₃)₂(PH₂SH)]CF₃SO₃ (1) is deprotonated in the presence of proton sponge to yield the neutral compound [CpRu(PPh₃)₂(PH₂S)] (2), where the thiophosphinite, PH₂S⁻, anion remains bound to the metal through the phosphorus atom. The parent complex 1 is easily restored in the presence of a weak acid. The sulfur of the coordinated anion may be alkylated with CF₃SO₃Me to yield [CpRu(PPh₃)₂(PH₂SCH₃)]CF₃SO₃ (3), the methyl thioester of the acid being bound to ruthenium through the phosphorus. The new compounds have been characterized by elemental analyses, IR and multinuclear NMR spectroscopy. The crystal structure of 2 · CH₃CN has been determined by X-ray diffraction methods.     

Application of samarium reagents in organic synthesis

Application of samarium diiodide, samarium triiodide, Sm0/auxiliary system and organosamarium reagents in organic synthesis was reviewed.     

Chemistry of antipyrine

This review is a literature survey of antipyrine, considered as one of the most valuable compounds in the fields of organic and medicinal chemistry. The biological importance, synthetic procedures, and reactions are discussed. Generally, the preparation of antipyrine was reported through the methylation of the corresponding 1H-pyrazolone following different reaction conditions. The reactions, in general, are electrophilic substitutions at C₄-position of pyrazolone. The mechanistic pathways of the reactions are surveyed.     

D-奎尼酸: 一个多用途的手性合成子

综述了D-奎尼酸在各种环状和链状生物活性化合物合成中的应用。奎尼酸分子中特有的顺式γ-羟基羧酸的结构单元提供了区别分子中各种羟基,以及进行其它区域选择性和立体选择性控制的方便途径。奎尼酸的结构特征以及其价廉、易得的优点,使之成为一个有用的而且重要的手性合成子。     

Some uses of mischmetall in organic synthesis

Mischmetall, an alloy of the light lanthanides, has been used in a variety of organic reactions, either as a coreductant in samarium(II)-mediated reactions (Barbier and Grignard-type reactions, pinacolic coupling reactions) or as the promoter of Reformatsky-type reactions. It has been also employed as the starting material for easy syntheses of lanthanide trihalides, the reactivity of which has been explored in Imamoto and Luche–Fukuzawa reactions and in Mukaiyama aldol reactions.     

Synthesis of 3β,3β,5‐tribromoacetyl‐4‐hydroxy‐6‐methyl‐2H‐pyran‐2‐one by Bromination of Dehydroacetic Acid

Abstract

Bromination of dehydroacetic acid giving rise to 3β,3β,5‐tribromoacetyl‐4‐hydroxy‐6‐methyl‐2H‐pyran‐2‐one is described.     

Trifluoromethanesulfonic acid in organic synthesis

The review analyzes data published in the past decade on the use of trifluoromethanesulfonic acid (triflic acid, CF₃SO₃H, TfOH) in organic synthesis, in particular in electrophilic aromatic substitution (Friedel–Crafts) reactions, formation of carbon–carbon and carbon–heteroatom bonds, isomerizations, syntheses of carboand heterocyclic structures, and other reactions, as well as in natural and organometallic compounds chemistry. The high protonating power and low nucleophilicity makes trifluoromethanesulfonic acid capable of generating from organic molecules cationic species which can be detected by spectral methods (NMR, IR spectroscopy, etc.), and their transformations can be studied. Experimental simplicity and efficiency of reactions promoted by trifluoromethanesulfonic acid make it a convenient reagent for the synthesis of new organic compounds.     

Recent developments in the chemistry of bicyclic 6-6 systems: Chemistry of pyrido[1,2-c]pyrimidines

The present review provides a study on the structural features, reactions, and synthetic methodologies of pyrido[1,2-c]pyrimidines. The maximum deviation from the mean plane of the pyridopyrimidine skeleton of 4-(pyridin-2-yl)-1H-pyrido[1,2-c]pyrimidine-1,3(2H)-dione indicated a reasonably planar system. The aim of this review is to give an overview of the diverse methodologies that have been reported on the chemistry of pyrido[1,2-c]pyrimidines. The different synthetic routes have been grouped according to the way the pyrido[1,2-c]pyrimidine moiety has been created. Thus, pyrido[1,2-c]pyrimidine compounds were obtained by the formation of one bond α to the bridgehead nitrogen atom [6+0(β)] and formation of two bonds from ([3+3], [4+2], and [5+1]) atom fragments. The mechanistic pathways of the reactions are discussed.     

m‐Metallaphenol: Synthesis and Reactivity Studies

Treatment of the osmium complex [Os{CHC‐(PPh₃)CH(OH)‐η²‐C≡CH}(PPh₃)₂(NCS)₂] ( 1 ) with excess triethylamine produces the first m‐metallaphenol complex [Os{CHC(PPh₃)CHC(OH)CH}(PPh₃)₂(NCS)₂] ( 2 ). The NMR spectroscopic and structural data as well as the nucleus‐independent chemical‐shift (NICS) values suggest that osmaphenol 2 has aromatic character. The reactivity studies demonstrate that 2 can react with different isocyanates to form the annulation reaction products [Os{CHC(PPh₃)CHC(O?C?ONR)C}(PPh₃)₂(NCS)₂] (R=Ph ( 3 ), iPr ( 7 ), Bn ( 8 )) via the carbamate intermediates [Os{CHC(PPh₃)CHC(O‐C?ONHR)CH}(PPh₃)₂(NCS)₂] (R=Ph ( 4 ), iPr ( 5 ), Bn ( 6 )). In addition, the similar annulation reactions can be extended to other unsaturated compounds containing N–C multiple bonds, for example, isothiocyanates, pyridine, and sodium thiocyanate, which can produce the corresponding fused osmabenzene complexes. In contrast, the reactions of 2 with common electrophiles, such as NOBF₄, NO₂BF₄, N‐bromosuccinimide, and N‐chlorosuccinimide only led to the decomposition of the metallaphenol ring. The experimental results suggest that 2 is very electrophilic and readily reacts with nucleophiles, which is mainly due to the metal center and the strong electron‐withdrawing phosphonium group.     

Removable directing groups in organic synthesis and catalysis

Directing groups have been widely used in recent years to achieve control over all aspects of reaction selectivity in a wide range of transformations involving transition-metal catalysis and organometallic reagents. In cases when the existing functional group within a substrate is unsuited to achieve efficient intramolecular delivery of a reagent or catalyst, the specific introduction of an appropriately designed removable reagent-directing group can be a solution to this problem. In this Review we give an overview of the state of the art in this area, including the stoichiometric and catalytic use of directing groups.     

Multicomponent coupling reactions for organic synthesis: chemoselective reactions with amide-aldehyde mixtures

The acid-catalyzed condensation chemistry of simple amides and aldehydes provides a highly prolific source of diverse reactants for irreversible follow-up reactions. Amide-aldehyde mixtures have been successfully employed in multicomponent syntheses of N-acyl alpha-amino acids (via palladium-catalyzed amidocarbonylation) and various cyclohexene, cyclohexadiene, and benzene derivatives (via the amide-aldehyde-dienophile (AAD) reaction).