Substitutions in the Presence of Metal Salts

Vinylic substitutions in otherwise unreactive systems can take place easily in the presence of metal salts. The chlorine atom of vinyl chloride is replaced by acetic acid, isopropyl alcohol and n-butylamine in the presence of catalytic amounts of PdCl2 in iso-octane (Stern et al., 1966). 

The mechanism was not specified but it was suggested that the reaction involved formation of a vinyl chloride-PdCl2 complex, which is followed 

The exchange of the acetate groups of vinyl acetate with those of CD3.C02H, which is catalysed by mercuric acetate, was claimed to involve direct displacement of the vinylic acetate (Samchenko and Rekasheva, 1965), although an electrophilic addition-elimination seems more plausible. 

The author is indebted to Drs. P. Beltrame, E. W. Cook, J. Klein, S. I. Miller, G. Modena, F. Montanari, J. D. Park, F. Theron, W. E. Truce and R. Vessiere for kindly making available unpublished data and for commenting on specific points. Thanks are especially due to Professor S. Patai who critically read the whole review, suggested the terms geminate and vicinal for the element effects, and made many valuable suggestions. 

Beltrame, P., and Beltrame, P. L. (1968). Oazz. chim. ital. 98, in press. 

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In the presence of metal salts, aryldiazo compounds undergo various coupling reactions in aqueous media. Such reactions have been used extensively in the dye and pigment industry and in anal d-ical chemistry. For example, the AICI3-catalyzed diazo couphng of three different 3-substituted-l//-pyrazol-2-in-5-ones in water with seven different aryldiazonium salts yielded 21 different (5-hydroxy-3-substituted-lFf-pyrazol-4-yl)-azobenzene derivatives as colored products with high yields (Eq. 11.67). ... 

The reaction of several a-diazoketones with ethyl vinyl ether under various conditions has been examined. In the presence of metal salts [Rh2(OAc)4, Pd(OAc)2, CuCl] ethoxy dihydrofurans are produced. The initial product of this reaction sequence is a cyclopropyl ketone which suffers from a spontaneous rearrangement to the dihydrofuran <96CJC2401>. An efficient synthesis of 3-acylfurans is achieved by Ag(I)/Celite mediated cycloaddition of dicarbonyl compounds with vinyl sulfide (<97TL5671> see also <97TL2095>). A two-step synthesis of 2-substituted 4-furanmethanol compounds was reported. The method involves a Homer-Wadsworth-Emmons reaction between 3-ketophosphonates and l,3-diacetoxy-2-... 

The cycloaddition of in sitM-generated azomethine yhdes with electron-deficient alkenes is a useful method for the generation of stereodefined, substituted pyrrolidines, and there has been some recent interest in the development of a catalytic asymmetric variant. While a variety of methods for the generation of azomethine ylides have been developed, treatment of an a-iminoester (8.200) with an amine base in the presence of metal salts is the process most commonly employed in the asymmetric variant, which generally uses an enantiomerically pure metal complex of copper, silver or zinc to give an N-metallated ylide (8.201) (Figure 8.6). ... 

The oxidative dearomatization of para-substituted o-alkynylanilines 290 using (diacetoxyiodo)benzene affords 2-alkynyl cyclohexadienimines 291, which can act as active substrates for reaction with electron-rich styrenes 292 in the presence of metal salts the Bi(OTf)3-catalyzed reactions give 3,4-dihydro-cyclopenta[c,rf indoles 293 and the AgOTf-catalyzed reactions provide tricyclic pyrrole derivatives 294... 

A remarkable case of a Meerwein reaction of phenylacetylene was reported by Leardini et al. (1985) in a new synthetic route to benzothiophene derivatives. Aryldi-azonium salts with a thioether group in the 2-position add phenylacetylene and substituted phenylacetylenes in the presence of metallic copper or iodide ion in acetone, or of FeS04 in DMSO (Scheme 10-60). The radical 10.21 formed initially is attacked intramolecularly by the sulfur atom of the thioether group to give the benzothiophene 10.22 in high yields (55-95%) as shown in (Scheme 10-60). Lear-... 

Similar photoinduced dimerizations and ligand substitutions in the presence of additives such as triphenylphosphine are observed with ion-pairs salts of Mn(CO)s and V(CO)6" with cobaltocenium or other cationic acceptors such as Ph2Cr", pyr-idinium, quinolinium, etc [118]. Most importantly, all photochemical transformations of the various carbonyl metallate salts are initiated by actinic light that solely excites the charge-transfer absorption bands of the contact ion pairs whereas local excitation of the separate ions is deliberately excluded. 

With Miscellaneous Compounds. Several mechanistic studies have been performed recently on reactions of "auxiliary stabilizers with 4-chloro-2-hexene, both in the presence and in the absence of metal salts (82,87,88, 89,90). The stabilizers used were phosphites (82,87), phosphines (82,87), epoxides (88), 2-phenylindole (89), and the bis(j8-aminocrotonate) ester of 1,4-butanediol (90). Important mechanistic features delineated in this work included substitutive removal of allylic... 

White granules. Soly in water depends on degree of substitution. Water-soluble CMC is available in various viscosities (5-2000 centipoises in I% soln), and the soly is equally good in hot and cold water (difference from methyl cellulose). Also the presence of metal salts has little effect on the viscosity. Solns are stable between pH 2 and 10. Below pH 2 precipitation of a solid occurs, above pH 10 the viscosity decreases rapidly. pKa 4.30. The free acid is obtainad from aq soln at pH 2.5 and may be precipitated with ajcohol. 

Of course, these schemes indicate only that the overall reactions may be classified as nucleophilic 1,3-substitutions and, in the last case, as electrophilic 1,3-substitut ions. The reactions often proceed only in the presence of catalytic or stoichiometric amounts of transition metal salts, while in their absence 1,1--substitutions or other processes are observed. The 1,1-substitutions are also catalyzed by salts of transition metals, and it is not yet well understood, which factors influence the 1,1 to 1,3-ratio. In a number of 1,3-Substitutions there is... 

Nucleophilic Substitution Route. Commercial synthesis of poly(arylethersulfone)s is accompHshed almost exclusively via the nucleophilic substitution polycondensation route. This synthesis route, discovered at Union Carbide in the early 1960s (3,4), involves reaction of the bisphenol of choice with 4,4 -dichlorodiphenylsulfone in a dipolar aprotic solvent in the presence of an alkaUbase. Examples of dipolar aprotic solvents include A/-methyl-2-pyrrohdinone (NMP), dimethyl acetamide (DMAc), sulfolane, and dimethyl sulfoxide (DMSO). Examples of suitable bases are sodium hydroxide, potassium hydroxide, and potassium carbonate. In the case of polysulfone (PSE) synthesis, the reaction is a two-step process in which the dialkah metal salt of bisphenol A (1) is first formed in situ from bisphenol A [80-05-7] by reaction with the base (eg, two molar equivalents of NaOH),... 

Substitution at the Carbon—Chlorine Bond. Vinyl chloride is generally considered inert to nucleophilic replacement compared to other alkyl halides. However, the chlorine atom can be exchanged under nucleophilic conditions in the presence of palladium [7440-05-3] Pd, and certain other metal chlorides and salts. Vinyl alcoholates, esters, and ethers can be readily produced from these reactions. 

Especially in the early steps of the synthesis of a complex molecule, there are plenty of examples in which epoxides are allowed to react with organometallic reagents. In particular, treatment of enantiomerically pure terminal epoxides with alkyl-, alkenyl-, or aryl-Grignard reagents in the presence of catalytic amounts of a copper salt, corresponding cuprates, or metal acetylides via alanate chemistry, provides a general route to optically active substituted alcohols useful as valuable building blocks in complex syntheses. 

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