Cp2TiCl2-catalyzed grignard exchange reactions with 1,3-dienes or styrenes. Preparation of allylic and α-arylethyl grignard reagents by a convenient and quantitative method

The addition of a catalytic amount of Cp₂TiCl₂ to an ether solution of propylmagnesium bromide and 1,3-dienes brings about an exchange reaction forming allylic Grignard reagents.Styrene also undergoes the exchange reaction under the same conditions affording α-phenethylmagnesium bromide.     

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 CH₂Cl₂ 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.     

Visible‐Light‐Induced Hydrodifluoromethylation of Alkenes with a Bromodifluoromethylphosphonium Bromide

Bromodifluoromethylphosphonium bromide was solely used as the precursor of difluorocarbene. Herein, an unprecedented visible‐light‐induced hydrodifluoromethylation of alkenes with bromodifluoromethylphosphonium bromide using H₂O and THF as hydrogen sources for the synthesis of difluoromethylated alkanes is described. This difluoromethylation is characterized by mild reaction conditions, ready availability of reagents, and excellent functional‐group tolerance.     

Etudes sur les composés organométalliques I action du chlorure de benzylmagnésium et du bromure de phénylmagnésium sur le tétrachlorure de titane

The reactions between phenylmagnesium bromide or benzylmagnesium chloride and titanium tetrachloride have been studied. The influence of the introduction order of the reagents is mentioned. Decomposition of the (non-isolated) compounds R_nTiX_4-n is shown to be essentially intermolecular, and rarely intramolecular.     

Action des organomagnesiens allyliques sur quelques thiocetones cyclisation de thiols β,γ-ethyleniques

Allylic Grignard reagents react with thioketones R₁R₂CS (thiobenzophenone, thiopivalophenone,thiopinacolone, thiocamphor and thiofe C(SH)-CHR-CHCH₂. These compounds give substituted thiolannes through radical cyclization. The ratio of diastereoisomeric thiols (and of subsequent isomers) has been measured in one case (thiopinacolone + crotylmagnesium bromide).     

General Synthesis of Ketones from Carboxylic Esters and Carboxamides by Use of Mixed Organolithium-Magnesium Reagents: Syntheses of Artemisia Ketone

The novel reagents formed by combination of Grignard reagents (RMgX) with lithium diisopropylamide (LDA) convert non-enolizable or slowly enolizable carboxylic esters or caboxamides into ketones which are protected from further reaction by their in situ conversion into enolates. These enolates can be trapped with electrophiles such as Me₃SiCl and allyl bromide. The scope of this Grignard mono-addition is illustrated by two direct syntheses of artemisia ketone ( 14 ).     

Reversed-phase thin-layer chromatography of 2-substituted benzoic acids with ammonium compounds as ion-pair reagents

Summary The retention behaviour of some substituted benzoic acids was tested on reversed-phase pre-coated plates in the presence of ammonium bromide and various tetraalkylammonium compounds with different alkyl chain lengths.It could be shown that the R_f values of the test compounds decrease in the absence and in the presence of ion-pair reagents with increasing water content of the eluent. The R_f values of the strongly acidic substituted benzoic acids decrease with both increasing concentration of the ion-pair reagent and with increasing chain length of the tetraalkylammonium compounds.Changing the inorganic counter-ions had no real influence on the separation and the size of R_f values when using tetramethylammonium compounds as ion-pair reagents.     

Etude de la fixation du groupe tertiaire gem-diméthylpropynyle HCCC(CH3)2 par voie organométallique; applications

Organometallics (CH₃)₂C=C=CHM (M = MgBr, Al Br, ZnBr) are easily prepared from the tertiary bromide (CH₃)₂C(Br)CCH. They often react to give only acetylenic products but, with some reagents, a mixture of acetylenic and allenic compounds is obtained.     

The separation of rhodium and iridium by ion flotation

Mixtures of iridium(IV) and rhodium(III) as IrCl^2-₆ and RhCl^3-₆ are separated by ion flotation. The iridium(IV) is selectively floated from aqueous solutions of pH 2 and 0.05% Ce(IV) with either hexadecyltripropylammonium bromide (HTPAB) or hexadecyltributylammonium bromide (HTBAB). The rhodium(III) does not float under the same conditions. The floated iridium sublate is collected in n-butyl acetate without contamination by the unfloated rhodium. Data are presented also for the separation and recovery of the Ir(IV) and Rh(III) with the above surfactants, hexadecyltrimethyl-ammonium bromide (HTMAB) and hexadecyltriethylammonium bromide (HTEAB) from solutions of various sodium chloride and hydrochloric acid concentrations. The use of solvent sublation for recovering the floated iridium is examined. The separation is fast, practical, simple and does not require expensive reagents or apparatus. For these reasons, the separation of iridium and rhodium by ion flotation offers advantages over previous methods.     

Rapid Synthesis of Alkoxyamine Hydrochloride Derivatives from Alkyl Bromide and N,N′-Di-tert-butoxycarbonylhydroxylamine [(Boc)2NOH]

The conventional route to alkoxyamine hydrochloride derivatives is by reaction of alkyl bromides with N-hydroxyphthalimide or N-hydroxysuccinimide followed by addition of hydrazine and HCl. Transformation of an alkyl bromide to the corresponding alkoxyamine hydrochloride can be accomplished more rapidly in good yields without using hazardous hydrazine by reaction of (Boc)₂NOH (N,N′-di-tert-butoxycarbonylhydroxylamine) and alkyl bromide followed by addition of HCl. Alkoxyamine hydrochlorides are powerful reagents in organic synthesis that can be used to synthesize alkoxyimino derivatives after condensation with a ketone or aldehyde.     

Synthesis of diaryl selenides using the in situ reagent SeCl2

Reactions of in situ prepared SeCl₂ with Grignard reagents (prepared from bromobenzene, o-tolyl bromide, 2,6-dimethyl-4-tert-butyl-1-bromobenzene, and 1-bromo-2-methylnaphthalene) and dilithiated benzamides (prepared from N-phenyl, N-cyclohexyl, and N-isopropyl benzamide) are described.     

Halomethyl—metal compounds : LXXII. The preparation of α-halocyclopropyl derivatives of lithium and their application in the synthesis of α-halocyclopropyl compounds of silicon,germanium, tin,lead, and mercury. A novel isomerization of syn-7-bromo-anti-7-lithionorcarane to the anti-7-bromo-syn-7-lithio isomer

A number of α-bromocyclopropyllithium reagents have been prepared at low temperature (?90° to ?100°) in THF or THF/Et₂O medium by reaction of n-butyllithium with the respective gem-dibromocyclopropane. Reactions of these new lithium reagents with concentrated HCl, trimethylchlorosilane, dimethyldichlorosilane, trimethyltin chloride, dimethyltin dichloride, dimethyldichlorogermane, trimethyllead bromide, mercuric chloride and some other organometallic halides are described. A novel isomerization of syn-7-bromo-anti-7-lithionorcarane to anti-7-bromo-syn-7-lithionorcarane, induced by the presence of a slight excess of 7,7-dibromonorcarane, is described.     

A procedure for Appel halogenations and dehydrations using a polystyrene supported phosphine oxide

The conversion of a commercially available polystyrene supported phosphine oxide into synthetically useful polymeric halophosphonium salts using oxalyl chloride/bromide takes place at room temperature in 5 min and generates only CO and CO₂ as by-products. The polymeric halophosphonium salts so obtained are useful reagents for Appel halogenations and other dehydrative coupling reactions. This gives rise to a simple three-step synthesis cycle for Appel and related reactions using a commercially available polymeric phosphine oxide with very simple purification and no phosphorus waste.     

One-pot synthesis of N-allylthioureas using supported reagents

A simple and efficient method has been developed for the synthesis of N-allylthioureas from allylic bromides in one-pot by using a supported reagents system, KSCN/SiO₂-RNH₃OAc/Al₂O₃, in which allyl bromide reacts first with KSCN/SiO₂ and the product, allyl isothiocyanate, reacts with RNH₃OAc/Al₂O₃ to give the final product, N-allylthiourea, in good yield.     

Zirconocene catalysis in the synthesis of 1,4-dimagnesium reagents: using competitive inhibition to suppress β-hydrogen abstraction

Substituted 1,4-dimagnesium reagents were synthesized by the zirconocene-catalyzed reaction of alkenes with ethylmagnesium reagents in the presence of a methylmagnesium containing additive. Improved selectivity for formation of dimagnesium reagents over monomagnesium reagents was obtained in the presence of the methylmagnesium containing additive. The ratio of mono- to dimagnesiated products was extrapolated from the ratio of alkene to diene in the products formed when the reaction was quenched with allyl bromide. The extent of the increase in the alkene/diene ratio was dependent on the type of organomagnesium halide, with greatest increases (59%) for the alkylmagnesium chlorides. A mechanism for improved selectivity by suppression of β-hydrogen abstraction in the catalytic cycle is presented. Quenching the 1,4-dimagnesium reagents with allyl bromide yielded decadienes.     

Comparaison de la reactivite du bromure d'ethylmagnesium et du diethylmagnesium vis-a-vis des cetones α,β-ethyleniques dans divers solvants

The reactivity of diethylmagnesium and ethylmagnesium bromide towards 2-cyclohexenone in various solvents is studied. The 1,2 addition is always predominant, but diethylmagnesium adds almost exclusively in 1,2 manner to this ketone while ethylmagnesium bromide gives both 1,2 and 1,4 addition products with a ratio dependent of the solvent basicity. Thus, in hydrocarbons (hexane, benzene), the magnesium reagents behave similary; and with more basic solvents, for EtMgBr the yield of the 1,4 addition product increases and that of the 1,2 addition product decreases.With another α,β-ethylenic ketone, trans-3-penten-2-one, 1,4 addition occurs predominantly with both magnesium reagents, diethylmagnesium and ethylmagnesium bromide, but diethylmagnesium gives again much more 1,2 addition product than ethylmagnesium bromide.     

Immobilized Enzyme Modules for Use in Analytical Microcalorimetry

Abstract

Immobilized enzyme modules designed for use in a conduction type analytical microcalorimeter were fabricated from cellulose acetate tubes and from cellulose filter paper. Catalase was bound to the modules after cyanogen bromide activation. Repetitive substrate determinations were made over a range of 0.015–1.2 mg of H₂O₂/ml of analytical solution. This was possible in spite of qualitative response differences relative to soluble enzyme reactions. The enzyme modules demonstrated excellent long term stability after repeated use and storage promising significant advantage for routine calorimetry using enzyme reagents.     

TBHP/R4N+X– promoted hydroaroylation of dialkyl azodicarboxylates with methyl arenes,aldehydes, aryl methanols and arylmethyl chlorides

Efficient TBHP/R₄N⁺X^– promoted hydroaroylations of dialkyl azo-1,2-dicarboxylates with methyl arenes, aldehydes, aryl methanols and arylmethyl chlorides are described. These oxidation/oxygenation and hydroaroylation processes were carried out by tert-butyl hydroperoxide as terminal oxidant/oxygen source, and were catalyzed by tetrabutylammonium bromide and tricaprylmethylammonium chloride as the driving force. During this investigation, all these hydroaroylating sources were found to be highly efficient reagents without the need of any transition-metal.     

The synthesis and some reactions of thiophene sulfides

The reaction of some electrophilic reagents (bromine, acetyl chloride, and acetic anhydride) and of butyllithium on the zinc chelate of 2-mercapto-3-thenylidenecyclohexylamine (IIIa) is examined. Bromination and acetylation of IIIa lead to fission of the chelate ring and the formation of a complex of thienoisothiazolium bromide with ZnBr₂ (VIII), and the corresponding dimienodithiocine (X). Butyllithium combines with the C=N double bond of the chelate ring (IIIa), with the formation of the chelate XIII.For part XVI, see [16].     

Synthesis of new C2 symmetrical dibenzospirodiamide and dibenzospirodiamine as potential chiral auxiliaries and building blocks of ionophores

2,8‐Diazadibenzo[c,i]spiro[5,5]undecan‐1,7‐dione 3 are synthesized via reaction of malonic ester with 2‐nitrobenzyl bromide, followed by reduction‐cyclization in 86% overall yield. 2,8‐Diazadibenzo[c,i]‐spiro[5,5]undecane 4 was obtained by reduction of 3 with LiAIH₄ in 90% yield. N‐Alkylation of 3 with various alkylating reagents is studied.