Palladium(II)-mediated routes to functionalised heterocycles

A series of allenic amines/amides 3 have been prepared and shown to undergo a palladium(II)-catalysed cyclisation, in the presence of carbon monoxide and methanol, to give α-(heterocyclic) acrylates 4.     

New routes to heterocycles via sulphenylation of unsaturated amides

Reaction of manganic acetate with organic disulphides in dichloromethane-trifluoroacetic acid in the presence of a variety of unsaturated amides leads to intramolecular cyclisation with formation of sulphenylated oxazolines, oxazines or tetrahydropyrroles.     

Synthesis of new fundamental heterocycles. Part VII. Synthesis of 2-azaxanthene

2-Azaxanthone ( 5 ) has been conveniently prepared by condensation of the morpholine enamine of 1-benzyl-4-piperidone witli salicylaldehyde followed by chromium trioxide oxidation and subsequent aromatization. Lithium aluminum hydride reduction of 5 afforded the new fundamental heterocycle 2-azaxanlhene.     

Synthesis of new polyaza heterocycles. Part 42: Diazines

Using Pd-catalyzed Stille cross-coupling reactions, we report here the synthesis of various mono- or bis(tri-n-butylstannyl)diazines which were reacted with various halogenated diazines to access to various polyaza heterocyclic derivatives.     

Intramolecular sulphonamidomethylation. Part II. Fused heterocycles from 2-phenylethanesulphonamides

1,2,4,5-Tetrahydro-3,2-benzothiazepine 3,3-dioxides 2 , with a variety of substituents on the nitrogen atom, can be easily obtained by the title reaction. The isomeric compounds 4–6 are also formed from sulphonamides bearing an N-aralkyl group with a chain of two or more carbon atoms. Activation of the ring closure-position or deactivation of the aromatic ring in the substituent can direct the reaction to give compounds 2 . Cyclization results are influenced by the size of the new heterocycle ring and by the predominant formation of derivatives with the SO₂ group outside the ring.     

New synthesis routes to 2-halopyridines. II. 2-bromopyridine

The use of bromine chloride (equilibrium mixture) in substitution reactions has been extended to heterocyclic substrates. The vapor phase bromination of pyridine (I) with bromine chloride at temperatures as low as 375° (carbon tetrachloride diluent) gave the following product distribution: 2-bromopyridine (IV) (75%) > 2-chloropyridine (VI) (21%) > 3-bromopyridine (II) (2.0%) ? 2,6-dibromopyridine (VI) (1.5%). In contrast, when bromine was employed in place of bromine chloride (450°; carbon tetrachloride diluent), product orientation was significantly altered to give nearly equal quantities of 3-bromopyridine (II) (17%) and 2-bromopyridine (IV) (22.7%).     

Synthesis of heterocycles. Part V. The synthesis of substituted indenopyridines

2-Arylmethylene-l-indanones (I) and 2-arylmethylene-1,3-indanediones (VII) react with active methylene compounds in the presence of ammonium acetate as a basic catalyst to afford substituted pyridines. The postulated routes to the formation of the reported compounds are given.     

Saturated heterocycles. Part 209. Synthesis of 1-cyclohexyl-substituted isoquinoline derivatives

In contrast with earlier literature data [7], both acrylic esters and acrylonitrile underwent Michael addition to l-methyl-3,4-dihydroisoquinolines 1-4 to yield the diesters 5-9 or the dinitrile 10 , respectively. Compounds 5-10 were converted by Claisen condensation to 1-[(3′-methoxycarbonyl- or 1-[(3′-ethoxycarbonyl-4′-oxo)-l'-cyclohexyl]-3,4-dihydroisoquinoline derivatives 11-16 . Several derivatives of 12 were prepared. The new compounds possess various pharmacological actions.     

Ring-closing metathesis: novel routes to aromatic heterocycles

Olefin metathesis has been established as an important and general reaction in synthetic organic chemistry. Recently, it has attracted interest as a powerful tool for the construction of aromatic heterocycles. The importance of heteroaromatic motifs in medicinal chemistry and biology, as well as the efficiency and wealth of metathesis transformations, have resulted in significant success in this rapidly developing area.     

Synthesis of phenylpyrrolylpyrroles. Part II

A series of methyl or ethyl 3-(N-arylpyrrol-3-yl)-1H-pyrrole-2-carboxylates and 2,4-dicarboxylates have been synthesized using an alkyl isocyanides addition-cyclization with N-arylpyrrole derivatives such as the carboxaldehydes and nitropropenes.     

Fluorine containing bioactive heterocycles. Part II. Synthesis of some new fluorine containing arylglyoxals,their hydrates and 1,5-disubstituted hydantoins

Eight new fluorine containing arylglyoxals have been synthesized by the oxidation of the active methyl group of fluorinated acetophenones by selenium dioxide in dioxan-water medium. The corresponding hydrates were obtained by dissolving arylglyoxals in minimum amounts of benzene and adding hot water. Seventeen new fluorine containing 1,5-disubstituted hydantoins were subsequently prepared by the condensation of these arylglyoxals with arylureas in ethanol and characterized by ir, pmr and mass spectral studies. Representative compounds have been screened for their possible anticonvulsant and analgesic activities. None of the compounds show significant analgesic acitivity.     

Synthesis of condensed quinoxalines. Part II

A novel efficient synthesis of fluorescent, fused quinoxalines was achieved. 7-Triazolyl-1,4-dioxino[2,3-b]-quinoxalines were synthesized by the diazotisation of 7-amino-1,4-dioxino[2,3-b]quinoxaline and coupling with selected aromatic amines followed by air oxidation. Diazotised aryl amines were coupled with 7-amino-1,4-dioxino[2,3-b]quinoxalines followed by subsequent air oxidation afforded 1,4-dioxino[2,3-b]quinoxalino-[6,5-d]1,2,3-triazoles. 7-Amino-1,4-dioxino[2,3-b]quinoxaline was condensed with conjugated enol ethers followed by cyclization in dowtherm resulted in 1,4-dioxino[2,3-b]quinoxalino[6,5-b]pyridines.     

Deacetalisation-bicyclisation routes to novel polycyclic heterocycles using stannous chloride dihydrate

The stannous chloride dihydrate-mediated deprotection-bicyclisation of a range of amides possessing a pendant acetal group is reported. These mild reaction conditions have been used to prepare a number of ring-fused heterocyclic compounds, some in enantiomerically pure form, which should be of interest both in their own right and as building blocks for the production of more complex target molecules.     

Picrylamino-substituted heterocycles. II. Furazans

This paper describes the synthesis of the various picrylamino- and nitro-substituted furazans and bifurazanyls. Except for 3,4-bis(picrylamino)furazan, which was obtained by nitrating 3,4-dianilinofurazan, the picrylaminofurazans were prepared by condensing the appropriate amino-furazan with picryl fluoride in the presence of triethylamine. The various aminofurazans were oxidized with peroxytrifluoroacetic acid to the corresponding nitro derivatives.     

Sulfur heterocycles. II. The hydroxyoxathiolane to acyloin rearrangement

Thermal control of demasking conditions may be used to convert hydroxyoxathiolanes into either α-hydroxyaldehydes or the corresponding ring-expanded acyloins.     

Synthesis and characterization of branched polystyrene. Part II. Fractionation

Fractionations have been carried out by a column-elution method on mixtures of linear and branched polystyrene. These had been prepared by anionic polymerization followed by a coupling reaction to form star-shaped branched polymers. Therefore, the components of the mixture were each of narrow distribution, and their molecular weights differed from each other as multiples of the original single chain length. For single chains in the 25,000–30,000 molecular weight range, separations were accomplished in which the multiples (number of branches) were 1, 2, 4, and 6. By this means, virtually monodisperse samples of the branched polymers could be isolated.     

Formazans in the synthesis of heterocycles. II. Synthesis of azines (Review)

The review is devoted to the use of formazans in the synthesis of azines.     

Aliphatic aldehydes in the synthesis of carbo- and heterocycles: Part II. Synthesis of six- and seven-membered rings, bicyclic compounds, and macrocycles

The review summarizes and systematizes data published over the past decade on the use of aliphatic aldehydes in the synthesis of six- and seven-membered carbo- and heterocycles, bicyclic compounds, and macrocycles. Biological activity and synthetic potential of the resulting compounds were also considered. The data are classed according to the ring type formed.