Ureidoalkylations and oxyalkylation of aromatic compounds with glyoxylic acid derivatives

The ureidoalkylation of benzene, toluene, xylene, anisole, phenol, acetanilide and chlorobenzene with N,N-dimethylurea-glyoxylic acid adducts 1 and 6 gives substituted N,N-dimethylcarbamoyl-DL-phenylglycine. The oxyalkylation of benzene with glyoxylic acid, methyl glyoxylate and methyl dimethoxyacetate is also described (see Table 1).     

Atom transfer radical cyclization (ATRC) applied to a chemoenzymatic synthesis of Quercus lactones

The natural fragrances (+)-trans whisky lactone 2 and (+)-trans cognac lactone 4, together with a minor amount of their (−)-cis stereoisomers, were prepared in 50% and 42% overall yield, respectively, starting from racemic 1-hepten-3-ol (±)-5 and 1-octen-3-ol (±)-6. The procedure involved first the enantioconvergent, lipase mediated transformation of the secondary allylic alcohols derived dichloroacetates (±)-7 and (±)-8 into the corresponding homochiral (+)-7 and (+)-8, combined with their cyclization under a transition metal catalyzed atom transfer process.     

Synthesis of 3-aminochroman derivatives by radical cyclization

[reaction: see text] Enantiomerically pure 5-acetyl-3-amino-3,4-dihydro-2H-1-benzopyran and methyl 3-amino-3,4-dihydro-2H-1-benzopyran-5-carboxylate were successfully synthesized starting from d- or l-serine. The formation of the benzopyran ring involved a radical cyclization step. The enantiomeric purities of the final aminochroman derivatives were determined by capillary electrophoresis using beta-cyclodextrins as a chiral selector.     

Synthesis of heterocyclic compounds by the cyclization of isatin and its derivatives (review)

Published data on the synthesis of heterocyclic compounds formed as the result of the recyclization of isatin and its derivatives are classified and summarized.Academician A. N. Kosygin Moscow State Textile Academy, Moscow. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 291–323, March, 1996. Original article submitted September 14, 1995.     

Hypervalent iodine(III)-induced intramolecular cyclization of alpha-(aryl)alkyl-beta-dicarbonyl compounds: a convenient synthesis of benzannulated and spirobenzannulated compounds.

A novel hypervalent iodine(III)-induced direct intramolecular cyclization of alpha-(aryl)alkyl-beta-dicarbonyl compounds has been described. Both meta- and para-substituted phenol ether derivatives containing acyclic or cyclic 1,3-dicarbonyl moieties at the side chain undergo this reaction in a facile manner. The reactions afford benzannulated and spirobenzannulated compounds that are of biological importance. The reaction is found to be general, mild, and high yielding. The mechanism of the reaction has been shown to involve a cation radical intermediate.     

Synthesis of derivatives of tetrahydrofuran and tetrahydropyran by intramolecular cyclization of unsaturated hydroxy compounds (review)

The literature data on reactions involving electrophilic heterocyclization of , -unsaturated alcohols, 2-allylphenols, oxiranes, aldehydes, and ketones are correlated. The factors that affects the reactivities of the unsaturated compounds (the structure of the substrate, the nature of the electrophile, and the nature of the solvent) in intramolecular cyclization are discussed. The problems of the regioselectivity of the addition and the stereochemistry of the resulting cyclization products are examined, and kinetic data are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1443–1462, November, 1982.     

Mn(III)/Cu(II)-mediated oxidative radical cyclization of alpha-(Methylthio)acetamides leading to erythrinanes

Treatment of N-[2-(3,4-dimethoxyphenyl)ethyl]-alpha-(methylthio)acetamide 3 with Mn(OAc)3 in the presence of Cu(OAc)2 gave tetrahydroindol-2-one 4, which then cyclized with Mn(OAc)3 to give 4-acetoxyerythrinane 5. A similar reaction of the 3,4-methylenedioxyphenyl congener 8 also gave tetrahydroindol-2-one 9, which, however, gave only a trace amount of the Mn(OAc)3-mediated cyclization product 11 and afforded the oxidation product 10. On the basis of these results, formation of 5 from 4 was thought to proceed via nucleophilic attack of the pyrrole ring on the cation-radical lX, generated by a single electron-transfer reaction of the acetoxy-substituted intermediate V. Treatment of compound 16 with Mn(OAc)3/Cu(OAc)2 gave no erythrinane derivative with recovery of the starting material, indicating that the presence of a methylthio group of 4 is essential for effecting the formation of erythrinane 5. On the other hand, treatment of 3 with Mn(OAc)3 using Cu(OTf)2 as an additive in place of Cu(OAc)2 gave another erythrinane 17. This method was applied to a formal synthesis of 3-demethoxyerythratidinone (20), a naturally occurring Erythrina alkaloid.     

Titanocene(III) mediated radical cyclization of α-bromo carbonyl compounds: synthesis of tri-substituted tetrahydrofurans

A novel and efficient methodology has been developed for the construction of synthetically important tri-substituted tetrahydrofuran derivatives from bromo-alkenes and bromo-alkynes by radical cyclization reactions using the radical initiator Cp₂TiCl, generated in situ from commercially available titanocene dichloride and Zn dust in tetrahydrofuran under argon.     

A new synthesis of α-amino acids—III: Amidoalkylation of active methylene compounds with glyoxylic acid derivatives

The synthesis of N-acyl derivatives of γ - keto - α - amino acids (3, 4, 5) by the amidoalkylation of 1,3-dicarbonyl compounds with glyoxylic acid-amide adducts (1, 2) is described. The γ - keto - α - amino acid derivatives (4, 5) were further converted to the corresponding butenolides (6, 7) and to pyrazolylglycine (12).     

Preparation of 1-thio uronic acid lactones and their use in oligosaccharide synthesis

The chemo- and regioselective TEMPO/BAIB-mediated oxidation of 2,6- and 3,6-dihydroxy 1-thio glycopyranosides to the corresponding 1-thio uronic acid lactones is described. These locked 1-thio glycuronides can directly be used as donors in glycosidation reactions using the Ph(2)SO/Tf(2)O reagent system. Alternatively, selective opening of the lactone bridge liberates a hydroxyl function for ensuing glycosylations.     

Photochemically induced electron transfer (PET) catalyzed radical cyclization: a practical method for inducing structural changes in peptides by formation of cyclic amino acid derivatives

A new radical cyclization reaction of unsaturated amino acid derivatives is presented. The reaction is induced by photoelectron transfer (PET) catalysis and proceeds, in comparison to commonly applied methods, under mild, nonoxidizing, and nontoxic conditions in neutral medium. This type of radical cyclization reaction can be used in peptide chemistry for inducing structural changes in peptides.     

An improved synthesis of 3-(1-imidazolyl)-2-alkenoic acid derivatives and related compounds

The preparative method of 3-(1-imidazolyl)-2-alkenoic acid derivatives and the related compounds was improved by the use of strong bases such as sodium hydride in DMF. By this improved method, the preparation of 2-substituted 3-(1-imidazolyl)-2-alkenoic acid derivatives was accomplished in good yields.     

Thiophenol-catalyzed Claisen rearrangement and radical cyclization: formation of furo- and pyrano-coumarin derivatives

Regioselective synthesis of dihydrofurocoumarins and dihydropyranocoumarins in excellent yields from 4-prop-2-ynyloxy coumarin via a thiol mediated radical reaction is described. Alkenyl radicals are generated from easily available terminal alkynes and thiophenol. Thiophenol catalyzed the Claisen rearrangement of the 4-prop-2-ynyloxycoumarin ethers.     

Platinum-promoted cyclization reactions of amino-olefins : I. The cyclization of 4-aminopentene and related compounds

Olefinic amines of the ytpe CH₂CH(CH₂)_nNHR undergo cyclization in acidic aqueous solution at 60°C in the presence of PtCl₄^2?. The PtCl₄^2? is regenerated at the end of the cyclization so that the reaction may be considered as catalytic. Both pyrrolidines and piperidines may be formed although the former are favored.     

Synthesis and characterisation of pentacoordinated ruthenium(II) hydrazone derivatives

Several new pentacoordinated ruthenium(II) compounds, Ru(PPh₃)₂L, of Schiff bases LH₂ are reported. The Schiff bases used have been derived from isonicotinoyl hydrazone and β-diketones or salicylaldehyde, or azines and mixed azines obtained from salicylaldehyde, benzoylacetone or 2-hydroxyacetophenone. These new compounds are highly coloured crystalline solids, stable and monomeric in toluene. They readily absorb carbon monoxide gas to give a carbonyl derivative of the type Ru(PPh₃)₂CO(L) in quantitative yields.     

Benzoyl hydrazone derivatives of niobium(V) and tantalum(V) ethoxides

Summary Niobium(V) and tantalum(V) pentaethoxides react with monofunctional benzoyl hydrazones (BHy) in refluxing benzene to give products of the type, M(OEt)_5–n(BHy)_n (where M=Nb or Ta and n=1, 2 or 3). The complexes have been characterised on the basis of elemental analysis, spectral (i.r. and n.m.r.) and molecular weight data.     

Two polymerizable derivatives of 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid)

[structure: see text] A versatile strategy for the synthesis of polymerizable derivatives of the redox-active indicator dye 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) is reported. Two products are shown to illustrate how the final step in the synthetic strategy can be used to alter the physical properties of the product. Both products were characterized spectroscopically and electrochemically. The hydrophilic monomer (sABTS) was polymerized, and the utility of this polymer (polyABTS) is demonstrated in the context of bioelectrocatalysis.     

Atom transfer radical cyclization reactions (ATRC): synthetic applications

Atom transfer cyclization reactions (ATRC) provide rapid access to functionalized γ-butyrolactones.