III reagents

Nucleophilic phosphorus(LII) reagents undergo 1,4-addition to ot,P-unsaturated carbonyl compounds (and other substrates susceptible to conjugate addition) to yield the corresponding y-functionalized organophosphorus compounds (e.g. 63).129 The precise course and outcome of the reaction depends upon the nature of the phosphorus nucleophile. 

Dialkyl phosphites and other Michaelis-Becker type reagents undergo conjugate additions readily in the presence of (substoichiometric) base (usually 

Regan and co-workers protocol for the synthesis of y-keto phosphinic acids by 1,4-addition of bis(trimethylsilyl)phosphonite (BTSP, 64) to a,p-unsaturated ketones avoids the isolation of pyrophoric BTSP 64 by generating it in situ. This procedure may be modified to synthesize disubstituted phosphinic acids by addition of a second a,p-unsaturated ketone.133 a,f)-Unsaturated esters are also suitable reactants.134 The products are isolated most conveniently as their adamantanammonium salts.133 

Caution Carry out all protocols in an efficient hood and wear disposable vinyl or latex gloves and chemical-resistant safety goggles at all times. 

Charge a three-necked round-bottomed flask (100 mL), equipped with a magnetic stirrer bar and fitted with a nitrogen inlet, septum and condenser, with ammonium phosphinate (2.5 g, 30.1 mmol) and hexamethyldisilazane (6.4 mL, 4.9 g, 30.1 mmol). Heat the stirred mixture at 100-110°C for 1-2 h, until evolution of ammonia has ceased. Caution ammonia is flammable, toxic and causes burns. 

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Transformations of heterocycles with C—C bond formation, involving organo-chromium(III) reagents 99CRV991. 

A similar approach was carried out reacting an enohzable ketone with amides in the presence of the hypervalent iodine(III) reagent (hydroxy(tosyl-oxy)iodobenzene, HDNIB) [48]. The reaction was carried out imder solvent-... 

When oxidized by iron(III) ions 4-aminoantipyrine reacts with phenols to yield colored quinonoid derivatives (cf. 4-aminoantipyrine — potassium hexacyanoferrate(III) reagent in Volume 1 a). It is an oxidative coupling based on the Emerson reaction. 

Olated Cr(III) reagents were prepared according to Equation 2 by reacting CrtNOg) with a calculated equivalent of NaOH. Chromic nitrate was used Decause the freshly prepared solution affords the hexaaqua Cr(III) cations. 

Only limited number of neutral monocyclic 11,3,2 diazaphosphole representatives have been reported, which have mostly been prepared by [4+1] cyclocondensation of diaminomaleodinitrile (DAMN) with P(III) reagent and the alkylation of the initially formed 1,3,2-diazaphospholide [2, 4, 7], During recent times, 67t-aromatic [l,3,2]diazaphospholium ions of type 46 [45], more often represented as cyclic phosphenium cation 47 [46,47], have attracted more attention due to their isoelec-tronic nature with Arduengo carbenes . Nature of bonding and aromaticity of these cations have been the subject of several experimental and theoretical studies (Structure 2) [48-52],... 

A Sml2-induced reductive cyclization of (V-(alkylketo)pyrroles provided an entry into medium ring 1,2-annelated pyrroles <06EJO4989>. An oxidative radical alkylation of pyrroles with xanthates promoted by triethylborane provided access to a-(pyrrol-2-yl)carboxylic acid derivatives <06TL2517>. An oxidative coupling of pyrroles promoted by a hypervalent iodine(III) reagent provided bipyrroles directly <060L2007>. 

Reduction of a-halo sulfides In combination with Lil, CrCl2 reduces a-halo sulfides to (a-alkylthio)chromium compounds, which undergo selective 1,2-addition to aldehydes (equation I). The [l-(phenylthio)ethyl]chromium(III) reagent ob-... 

This iodine (III) reagent is obtained in 90% yield by reaction of C6H5I(OAc)2 with diphenyl phosphate, (C6H50)2P02H, in aqueous CH,CN. 

Niobium(III) chloride-Dimethoxyethane, NbCl3 DME (1). This soluble Nb(III) reagent is obtained as a brick-red solid by reduction of NbCl> in DME with Bu,SnH. 

Organocerium(III) reagents, RCeX2. These reagents are obtained in situ by reaction of RLi with Cel, or CeCl3. 

PheOMe)]3+ reagent (rather than A), a higher AA OMe concentration, and a shorter reaction time. It is likely that the Mensi and Isied result arises largely from using the racemic A,A-Co(III) reagent. 

The Co(III) reagent can be readily removed by chemical or electrochemical (preferred) methods. 

III. Reagent-Dependent Regioselective Control in Multiple Carbohydrate Esterifications... 

A hypervalent iodine(III) reagent, Ph—1=0, together with TMS-azide, promotes direct a-azidation of cyclic sulfides the reaction opens up a route to unstable N,S-acetals. ... 

Various transition metals have been used in redox processes. For example, tandem sequences of cyclization have been initiated from malonate enolates by electron-transfer-induced oxidation with ferricenium ion Cp2pe+ (51) followed by cyclization and either radical or cationic termination (Scheme 41). ° Titanium, in the form of Cp2TiPh, has been used to initiate reductive radical cyclizations to give y- and 5-cyano esters in a 5- or 6-exo manner, respectively (Scheme 42). The Ti(III) reagent coordinates both to the C=0 and CN groups and cyclization proceeds irreversibly without formation of iminyl radical intermediates.The oxidation of benzylic and allylic alcohols in a two-phase system in the presence of r-butyl hydroperoxide, a copper catalyst, and a phase-transfer catalyst has been examined. The reactions were shown to proceed via a heterolytic mechanism however, the oxidations of related active methylene compounds (without the alcohol functionality) were determined to be free-radical processes. 

Operationally, the relevant reagents are easy to prepare, safe, and economical. The by-product. Phi, is easy to separate and, in principle, could be reoxidized. Furthermore, most of the reactions described are potentially scalable to multikilogram levels. A next step in this methodology would be catalytic regeneration of the I(III) reagent, that is. 

This chapter is an update (2003 to present) of the main applications of Bi(III) Lewis acids in organic synthesis developed and, in some cases, co-developed, by French and Portuguese research groups. Thus, in this chapter, the preparation of Bi(III) catalysts and their application to chemical transformations ranging from electrophilic addition to cyclization reactions, will be reviewed. The development of new environmentally friendly chemical processes, using Bi(III) reagents and catalysts, with direct application to steroid chemistry and related compounds will also be considered. 

Resin-bound triarylbismuth(III) reagents have been prepared for solid phase organic synthesis [72, 73]. As shown in Sect. 2.5, triarylbismuths are efficient... 

Thorium coprecipitated from acidified sample with Fe(OH)3, clean-up Th by selective solvent extraction, coprecipitated with Al(OH)3 and develop color by Arsenazo III reagent. After color development, coprecipitate Th with LaF3. 

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