Nucleophiles and reactions

The sulfur atom of the thiocarbonyl group is a good nucleophile, and reaction between benzyl bromide and l-(2-thiazolyl)thiourea yields the isothiouronium salt (496). The sulfur atom may also be engaged in a chelate, as exemplified by the Cu chelate of 2-thioureido-4-methylthiazole (491). These chelates with metal ions were thoroughly studied in acidic, neutral, and alkaline media for 66 metal ions in order to define their analytical use. They are formed in the molar ratio of 1 2 for metal II compounds (498). 

Sulfates. The chemistry of alkyl sulfates is dominated by two fundamental process types reaction with nucleophiles and reaction as acids. Reaction with nucleophiles results in alkylation. 

Alkylation of thiolate anions by bromochlorodifluoromethane generally follows this mechanism [55, 57] However, depending on the nature of the nucleophile and reaction condibons, disubstimtion can arise by a SET process [57] (equation 49)... 

The iminium salts are of course especially Subject to attack by nucleophiles, and reactions of this type are discussed in Chapter 5. See also Section V.H. 

Nucleophilic reactivity toward Pt(II) complexes may be conveniently systematized via linear free energy relationships established between reactions of trans Ptpy2Cl2 (py = pyridine) with various nucleophiles and reactions of other Pt(II) complexes with the same nucleophiles. First, each nucleophile is characterized by a nucleophilicity parameter, derived from its reactivity toward the common substrate, trans Ptpy2Cl2. Reactivity toward other Pt(II) substrates is then quite satisfactorily represented by an equation of the form (21), wherein ky is the value of in the reaction with nucleophile Y... 

The electrophilic addition of iodine donors to 1,5-cyclooctadiene (3) gives, analogously to those of BrX, a product distribution which is strongly dependent on the nature of the nucleophile and reaction conditions. 

Allylic substitution with free carbamate nucleophiles was not accomplished until advanced catalyst precursors were developed. However, products from substitution with carbamate nucleophiles were generated by a decarboxylative allylation. In this process, the imidodicarbonate was shown to undergo decarboxylation to form the carbamate nucleophile, and reaction of the resulting carbamate with the 7i-allyliridium intermediate formed branched allylic carbamate products (Scheme 17) [92, 95]. 

A chemical reaction Is the result of competition It Is a race that Is won by the fastest runner. A collection of molecules tend to do, by and large, what Is easiest for them. An alkyl halide with p-hydrogen atoms when reacted with a base or a nucleophile has two competing routes substitution (Sj,jl and Sj,j2) and elimination. Which route will be taken up depends upon the nature of alkyl halide, strength and size of base/nucleophile and reaction conditions. Thus, a bulkier nucleophile will prefer to act as a base and abstracts a proton rather than approach a tetravalent carbon atom (steric reasons) and vice versa. 

Hence, a reaction of Type I will involve a racemic or achiral/me,t(9 nncleophile which will react enantioselectively with an achiral acyl donor in the presence of a chiral catalyst, while on the other hand, a reaction of Type II will associate an achiral nncleophile and a racemic or udm lmeso acyl donor in the presence of a chiral catalyst. In both cases, when a racemic component is implicated the process constitntes a KR and the maximum theoretical yield of enantiomerically pure product, given perfect enantioselectivity, is 50%. When an achiral/mera component is involved, then the process constitutes either a site-selective asymmetric desymmetrisation (ASD) or, in the case of tt-nucleophiles and reactions involving ketenes, a face-selective addition process, and the maximum theoretical yield of enantiomerically pure product, given perfect enantioselectivity, is 100%. 

The reactivity and orientation of nucleophilic attack on fluoroolefins are determined by the stability of the possible carbamon intermediates Fluoroolefins react regioselectively with nucleophiles so as to maximize the number of fluorines (3 to the electron-rich carbon in the transition state The reactivities increase in the order CF2=CF2 < CF2=CFCF3 CF2=C(CF3)2 and CF2=CF2 < CF2=CFC1 < CF2=CFBr, and nucleophdes attack exclusively at the CF2= end of these olefins [129,141] The regiochemistry of nucleophilic attack normally is predictable, but the product distribution arising from addition and addition-elimination pathways depends upon the olefin, nucleophile, and reaction conditions (equations 13-15) The various factors that control product distributions have been reviewed [142,143 144]... 

In addition to the typical behavior exhibited in a wide array of reactions by the carbonyl group, attack by nucleophiles and reactions leading to C—S single bonds are generally favored. The energetic reasons for this behavior have been discussed in Section II. Likewise, thiocarbonyl groups show a rich variety of cycloaddition reactions, ranging from... 

Given an alkyl halide with a particular stereochemistry, a nucleophile, and reaction conditions, predict the stereochemistry of the product of nucleophilic substitution. 

Where the nucleophile is a second molecule of oxetane, a chain reaction occurs leading to the formation of polymers, as discussed in Section 2.05.6.4.3. However, oxetanes can also be ring-opened by a wide range of alternative nucleophiles, and reactions of this nature make oxetanes an important synthetic intermediate. 

Reactions with BH4 always involve the loss of H and a pair of electrons using the BH bond as nucleophile and reactions with NH4 always involve the loss of H without a pair of electrons using the NH bond as electrophile. 

Methyl iodide easily undergoes Sfj2 reactions since it is very unhindered amines are weak nucleophiles, and reaction gives the ammonium intermediate which is deprotonated to give the methylamine product. 

There are exceptions to this rule, however, particularly when the electrons on the carbon of cyanide are tied up in a covalent bond. Both silver cyanide (AgCN) and cuprous cyanide (CuCN) have bonds between the metal and carbon (Ag-C or Cu-C) that have significant covalent character. The Ag and Cu ions are not charge dense, and they prefer to coordinate to atoms that are also not dense in charge (the C end of cyanide). If the metal-carbon bond in M-CN is covalent, the electrons on carbon are shared and less available for donation, which makes carbon less nucleophilic. In both AgCN and CuCN, the nitrogen atom is more nucleophilic and reaction with an alkyl halide R-X leads to a molecule called an isocyanide (or isonitrile, R-+N=C ). Isocyanides and the reaction of such compounds are not discussed in this hook. 

Acylamino acid derivatives with a leaving group in the P-position, such as N-acyl-O-tosylserine, undergo substitution reactions with nucleophiles. According to the leaving group, nucleophile and reaction conditions, the reaction can proceed via a nucleophilic substitution with retention of configuration or elimination/addition with racemization (see section IV. A. 2.1). 

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