Treatment Of Bromides Research Articles

Silver-catalyzed cross-coupling reactions of alkyl bromides with alkyl or aryl Grignard reagents

Treatment of secondary or tertiary alkyl bromides with alkyl Grignard reagents in the presence of catalytic amounts of silver bromide and potassium fluoride in CH 2Cl 2 afforded the corresponding cross-coupling products in reasonable yields. Moreover, silver showed catalytic activity for the cross-coupling reactions of alkyl bromides with aryl Grignard reagents.

Improved chemoselective, ecofriendly conditions for the conversion of primary alkyl halides into nitroalkanes under PEG400

Treatment of primary alkyl bromides or iodides with 1.5–3 equivalents of sodium nitrite, at room temperature, in PEG400 as solvent, allows the chemoselective formation of primary nitroalkanes in satisfactory to good yields, under ecofriendly reaction conditions.

Synthesis of allylic thiocyanates and novel 1,3-thiazin-4-ones from 2-(bromomethyl)alkenoates and S-nucleophiles in aqueous medium

Allylic thiocyanates and novel heterocycles containing the 1,3-thiazin-4-one core are easily obtained in high yields and mild conditions by nucleophilic displacement of 2-(bromomethyl)alkenoates (derived from Morita–Baylis–Hillman adducts) with sulphur-centred nucleophiles in aqueous acetone at 25 °C. Treatment of allylic bromides with NaSCN gave the corresponding ( Z)-2-(thiocyanomethyl)alkenoates, while the reaction with thiourea followed by a basic work-up selectively produced (5 Z)-2-amino-5-arylidene-1,3-thiazin-4-ones. The structural assignments were confirmed by X-ray diffraction analysis.

Efficient Construction of Biaryls and Macrocyclic Cyclophanes via Electron-Transfer Oxidation of Lipshutz Cuprates

An efficient method for the homocoupling of aryl halides by electron-transfer oxidation of Lipshutz cuprates (Ar2Cu(CN)Li2) with organic electron acceptors is disclosed. Thus, various types of Lipshutz cuprates are prepared by successive treatment of aryl or heteroaryl bromides with tert-butyllithium and CuCN. The electron-transfer oxidation of Lipshutz cuprates with p-benzoquinones proceeds smoothly to afford the corresponding homocoupling products in moderate to good yields. Furthermore, it can be applied to the construction of either thiophene- or benzene-fused 10-membered ring cyclophanes. For the synthesis of 10-membered cyclophanes, the linear C-Cu-C structure of Lipshutz cuprates should be maintained in the dimetallacyclic intermediates, producing the large ring cyclophanes efficiently. The X-ray analysis of the cyclophanes reveals that the difference in the bridging atoms results in the different conformations of the macrocyclic rings. Thus, the silicon-bridged cyclophane 5a adopts a D2-symmetric structure with a twisted rhombic arrangement of four thiophene rings, whereas the methylene- and oxygen-bridged cyclophanes 5b and 5c possess C2h- and C2-symmetric structures with chair- and boatlike conformations, respectively. The 1H NMR spectrum of C2-symmetric 5c is temperature-dependent, and the activation energy (DeltaG) for the conformational change is 10.1 kcal/mol.

A rapid and high-yielding synthesis of thiazoles and aminothiazoles using ammonium-12-molybdophosphate

A convenient method for the synthesis of thiazoles and aminothiazoles by treatment of phenacyl bromides with thioamides/thiourea in the presence of ammonium-12-molybdophosphate at room temperature has been developed. The products are formed rapidly (within 20min) and in excellent yields.

A Practical Synthesis of Highly Functionalized Aryl Nitriles Through Cyanation of Aryl Bromides Employing Heterogeneous Pd/C: In Quest of an Industrially Viable Process.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A practical synthesis of highly functionalized aryl nitriles through cyanation of aryl bromides employing heterogeneous Pd/C: in quest of an industrially viable process

Preparation of aryl nitrile 2a through classical Rosenmund-von Braun reaction of aryl bromide 1a resulted in a poor yield (61%) due to a high reaction temperature (165 °C) and a lack of efficient procedure for separating 2a from a large quantity of heavy metal waste (Cu salts). To address these issues, a practical synthesis of multifunctional aryl nitriles through cyanation of aryl bromides has been developed with heterogeneous Pd/C used as the catalyst. Treatment of aryl bromides 1 with Zn(CN) 2 in the presence of Pd/C, Zn, ZnBr 2 and PPh 3 in DMA provided aryl nitriles 2 involving those carrying sterically demanding electron-rich substituent in good yields and in highly reproducible manner. The activity of Pd/C is highly dependent on the properties of the Pd/C. Oxidic thickshell type catalyst Pd/C D5 was found to furnish the highest rate acceleration and yield. The use of heterogeneous Pd/C might anchor and disperse Pd over the solid support of the catalyst, at least in the initial stage of the reaction, to assure the formation of monomeric Pd complex without precipitating to inactive Pd black. The use of a slightly excess of Zn(CN) 2 (0.6 equiv) and air oxidation of phosphine ligand, after end of the reaction, converted Pd species to insoluble phosphine-free Pd cyanides, from which Pd was recovered in high yield through simple filtration followed by usual recovery process involving combustion.

Cascade radical synthesis of heteroarenes via iminyl radicalsElectronic supplementary information (ESI) available: additional experimental details. See http://www.rsc.org/suppdata/p1/b1/b108323f/

A novel cascade cyclisation protocol has been developed which ‘zips up’ two rings to form new tetracycles. In the protocol, treatment of vinyl bromides and iodides with hexamethylditin (Me3Sn˙) yields intermediate vinyl radicals which undergo 5-exo cyclisation onto nitrile groups to yield intermediate iminyl radicals. The iminyl radicals can undergo 6-endo cyclisation (or 5-exo followed by neophyl rearrangement) to yield tetracyclic π-radicals which lose hydrogen (H˙) in an H-abstraction step. Methyl radicals, generated from the breakdown of trimethylstannyl radicals (Me3Sn˙), are proposed as a possible H-abstractor for this final oxidative step. The protocol has been used to synthesise the tetracyclic rings A–D (tetracycle indolizino[1,2-b]quinolin-9(11H)-one) of the anticancer alkaloids camptothecin, mappicine, nothapodytine B and nothapodytine A. The protocol has also been applied to the synthesis of analogues of camptothecin in which ring A has been replaced by thiophene (8,10-dihydrothieno[2′,3′:5,6]pyrido[2,3-a]indolizin-8-one) and ring D by pyrrole (10H-pyrrolizino[1,2-b]quinoline) and benzene (11H-indeno[1,2-b]quinolin-11-one).

8‐Phenyl‐10,10a‐dihydropyrido[1,2‐ a ]azepines by 1,7‐Electrocyclization of Conjugated Pyridinium Ylides—Rationalization of the Periselectivity

Base treatment of the pyridinium bromides 11 a–e gives rise to the formation of the dihydropyridoazepines 14 a–e as the only monomolecular products. The reaction takes place by initial deprotonation to the ylides 12, which undergo 8π-electrocyclization affording the seven-membered-ring systems; no products of a dipolar 6π-cyclization were detected. On the basis of quantum mechanical calculations a rationalization of the periselectivity of the electrocyclization process is given.

A New Approach to Some 1,6-Dideoxy 1,6-Epithio Sugars

The treatment of hexopyranosyl bromides, also activated at C6 (Br, OTs, OMs), with H2S/HCONMe2 under basic conditions gives rise to 1,6-dideoxy 1,6-epithio sugars. One such sugar has been further transformed into the synthetically useful 3,4-anhydro-1,6-dideoxy-1,6-epithio-β-D-galactose. The treatment of this epoxide with sodium azide and with cyclohexylamine is described. An analogous treatment of one doubly activated hexopyranosyl bromide with sodium hydrogen selenide has led to a novel 1,6-dideoxy 1,6-episeleno sugar which displayed interesting n.m.r. spectra. Finally, in an attempt to prepare 1,6-dideoxy 1,6-epidithio sugars, a tetraalkylammonium tetrathiomolybdate reagent was found to be the reagent of choice for converting doubly activated hexopyranosyl bromides into 1,6-dideoxy 1,6-epithio sugars.

Stereocontrolled synthesis of β-hydroxyphenylalanine and β-hydroxytyrosine derivatives

Side-chain bromination of N-phthaloyl-( S)-phenylalanine and tyrosine derivatives, followed by treatment of the product bromides with silver nitrate in aqueous acetone, affords the corresponding (2 S,3 R)-β-hydroxy-α-amino acids, enantiospecifically and diastereoselectively. The diastereoselectivity depends on the carboxyl protecting group. tert-Butyl esters display greater stereoselectivity than the corresponding methyl esters, presumably as a result of a steric effect, while N-tert-butylamides react diastereospecifically due to a combination of steric and electronic effects.

Design and application of a molecular mechanics force field for alkyl iodides including an electrostatic polarization model

AbstractWe describe a force field extending Boyd and Kesner's molecule mechanics treatment of alkyl chlorides, fluorides and bromides to alkyl iodides: accordingly, as well as parameters for the potential energy of bond stretching and bending and for interactions between nonbonded atoms, the field includes parameters taking into account permanent and induced C‐I dipoles, whose values have been estimated by fitting the model to experimental dipole moment data. The results of applying this force field to 22 organic iodides comprising several substitution series are reported, and the structural and energy trends in the various series are discussed. These results agree satisfactorily with available experimental data and with those obtained by A. Y. Meyer using a different kind of force field.

Indole alkaloid synthesis; a stereospecific preparation of functionalised cis-hexahydrocarbazoles

Treatment of oxindole bromides (4) and (6) with t-butyl-lithium followed by reduction with lithium aluminium hydride gave the cis-4a-methylhexahydrocarbazoles (11) and (13).

ChemInform Abstract: Reactions of Tris(trimethylsilyl)methylsilicon Compounds with Organolithium Reagents.

AbstractReaction of the trisylsilane (III) with the phenyllithium derivatives (II), formed by treatment of the aryl bromides with butyllithium in hexane, gives rather low yields of the trisylarylsilanes (IV).

ChemInform Abstract: Preparation of New Nitrogen‐Bridged Heterocycles. Part 15. Synthesis and Reaction of 1,9a‐Dihydropyrido(2,1‐c) (1,4)thiazines.

AbstractAlkaline treatment of the pyridinium bromides (III), obtained by S‐alkylation of the methylides (I) with corresponding alkyl bromides (II), gives smoothly the dihydropyridothiazine derivatives (V) and (VI) as isomeric mixtures.

ChemInform Abstract: PALLADIUM‐CATALYZED NEW CARBON‐PHOSPHORUS BOND FORMATION

AbstractDie Pd‐katalysierte Reaktion der Arylhalogenide (II) mit den Dialkylphosphiten (III) in Gegenwart von Triethylamin ergibt die Dialkyl‐arylphosphonate (I).

Palladium-catalyzed New Carbon-Phosphorus Bond Formation

Abstract Dialkyl arylphosphonates are prepared by the palladium-catalyzed reaction of aryl bromides with dialkyl phosphite in the presence of triethylamine. The similar treatment of vinyl bromides gives dialkyl vinylphosphonates stereoselectively.

SYNTHESIS OF PHOSPHONIC DICHLORIDES AND CORRELATION OF THEIR P-31 CHEMICAL SHIFTS

Abstract Various mono-substituted diethyl arylphosphonates were prepared in good yield by treatment of aryl bromides or iodides with triethyl phosphite in the presence of NiCl2 or alternatively, addition of the aryl grignard reagent to diethyl phosphorochloridate. These esters were then converted into the appropriate phosphonic dichlorides by standard methods. Para-substituted phosphonic dichlorides were also prepared by dimethylsulfoxide oxidation of phosphonous dichlorides which were prepared by Friedel-Crafts reaction of PCl3 with the substituted benzene. The P-31 chemical shifts of these phosphonic dichlorides were correlated with Hammett (σn) and Taft (σo) values. The shielding of the phosphorus resonance signal by electron withdrawing groups was rationalized by increased P[dbnd]O bonding. The observed shielding of ortho-substituted arylphosphonic dichlorides was rationalized by a gamma effect.

Reactions of bromine and lead tetra-acetate with 2-(substituted hydrazino)-5-phenyl-1,3,4-oxadiazoles: routes to 3-aryl-6-phenyl-1,2,4-triazolo[3,4-b][1,3,4]oxadiazoles

2-(Substituted hydrazino)-5-phenyl-1,3,4-oxadiazoles react with bromine in acetic acid to yield hydrazone perbromides, or hydrazonyl bromides in the presence of sodium acetate. Treatment of the hydrazonyl bromides with triethylamine in benzene or solvolysis in aqueous solvents results in cyclisation to the new 1,2,4-triazolo[3,4-b]-[1,3,4]oxadiazole ring system. The cyclisation involves the oxadiazole ring as a nucleophile which attacks the labile carbon–bromine site in the hydrazonyl bromide. In the solvolysis, this internal nucleophilic attack is in competition with external nucleophilic attack by solvent molecules, and direct solvolysis products are also obtained. A second route to the new ring system with tribromodiazabutadienes has also been developed. The oxadiazole ring of the new 1,2,4-triazolo[3,4-b][1,3,4]oxadiazoles is labile to acid and base and a preferential ring interconversion pattern of oxadiazole to triazole has been noted. In the reaction of the 2-(substituted hydrazino)-5-phenyl-1,3,4-oxadiazoles with lead tetra-acetate, the presence of the oxygen atom at the potential cyclisation site inhibits the cyclisation. The'reaction instead involves acetoxylation of the hydrazone and only gives, at most, traces of 1,2,4-triazolo[3,4-b][1,3,4]oxadiazoles.

Synthesis of orotic acid from maleuric acid

The bromination of maleuric acid or its methyl ester, with subsequent alkaline treatment of the intermediate bromides, leads to the formation of orotic acid.