Linear nucleophilic additions

The kinetics of the hydrolysis of some imines derived from benzophenone anc primary amines revealed the normal dependence of mechanism on pH with ratedetermining nucleophilic attack at high pH and rate-determining decomposition of the tetrahedral intermediate at low pH. The simple primary amines show a linear correlation between the rate of nucleophilic addition and the basicity of the amine Several diamines which were included in the study, in particular A, B, and C, al showed a positive (more reactive) deviation from the correlation line for the simple amines. Why might these amines be more reactive than predicted on the basis of thei ... 

Qualitative models of reactivity and quantum mechanical calculations of reaction paths both indicate an angular approach of the attacking nucleophile to the first-row sp -hybridized electrophilic centers M at intermediate and reactive distances, 29. The geometry of 29 is also characteristic for the case of nucleophilic addition to electron-deficient centers of main-group 12 and 13 elements. By contrast, a linear arrangement 30 of making and breaking bonds is required for sp -hybridized first-row centers (C, N, O)... 

B. l,3>2>Dioxaphospholens.—The kinetics of the addition of trialkyl phosphites to benzil have been investigated spectrophotometrically. The second-order reaction of trimethyl phosphite in dioxan has activation parameters of A// = 8.4 kcal mol and AS = — 47.5 e.u. In benzene the rate constant increases linearly with low concentrations of added organic acid and decreases linearly with low concentrations of added base. The Diels-Alder mechanism is considered unlikely on the basis of these data, and the slow step is considered to be nucleophilic addition of the phosphite to the carbon of the carbonyl group (see Scheme). 

Sander and Jencks introduced a linear free energy relationship for nucleophilic addition to carbonyls. The equilibrium nucleophilicity of a species HNu is given by... 

Based on the assumption that this reaction goes through Jt-allyl Mo intermediates (A and B), the result from either linear carbonate (L-C) or branched carbonate (B-C) should give exactly the same result if the equilibrium between A and B is much faster than nucleophilic addition of sodium dimethyl malonate to A or B (Curtain-Hammett) as shown in Scheme 2.17. 

In the examples presented so far, only two enantiomeric products have been possible in each case, since the substrates have all contained identical substituents on the Cl and C3 positions. However, a more complex situation occurs when the allyl system is unsymmetrically-substituted, as in 43a or 43b (Scheme 12).1161 Here, nucleophilic addition to the corresponding ri3-allyl intermediate 44 may afford an achiral, linear product 45, in addition to the pair of enantiomeric branched products 46. 

The linear telomerization reaction of dienes was one of the very first processes catalyzed by water soluble phosphine complexes in aqueous media [7,8]. The reaction itself is the dimerization of a diene coupled with a simultaneous nucleophilic addition of HX (water, alcohols, amines, carboxylic acids, active methylene compounds, etc.) (Scheme 7.3). It is catalyzed by nickel- and palladium complexes of which palladium catalysts are substantially more active. In organic solutions [Pd(OAc)2] + PPhs gives the simplest catalyst combination and Ni/IPPTS and Pd/TPPTS were suggested for mnning the telomerizations in aqueous/organic biphasic systems [7]. An aqueous solvent would seem a straightforward choice for telomerization of dienes with water (the so-called hydrodimerization). In fact, the possibility of separation of the products and the catalyst without a need for distillation is a more important reason in this case, too. 

Thermolysis of 3-(ort o-anisoyl)-l-(l-piperidinyl)-3-cyclobutenes 807 in the presence of mesitylene affords angular-fused xanthones 809 via formation and ring closure of the intermediate 808 (Scheme 226) <1997TL3663>. Linear-fused xanthones 810 are prepared by nucleophilic addition of aryl and heteroaryl lithiates to dithiane protected benzopyrone-fused cyclobutenediones 811 followed by hydroysis of the dithiane protecting group (Scheme 227) <1996JA12473>. 

Jencks (1972, 1969b) has proposed a model which maintains the significance of a as a measure of transition state structure and yet provides a very elegant rationalization of the fact that linear Br nsted plots are often obtained over large reactivity ranges, both by variation in catalyst pKa and substrate reactivity. Jencks noted that the acid catalysed nucleophilic addition to carbonyl compounds (21) yielded linear Br nsted plots (in apparent violation of the reactivity-selectivity principle) yet as the basicity of the nucleophile N was increased the Br nsted slope decreased (in agreement with the... 

It should be stressed that several cyclopropylideneamines 28 have been generated in situ from a-haloimines 3 under basic Favorskii conditions and that nucleophilic addition of the bases used (e.g. alkoxides, hydroxide) led to adducts 29 which, in most cases, were not isolable. Instead, they readily open to give the most stable carbanions (30 or 31). This feature accounts for the formation of branched amides 33 from aliphatic a-halo ketimines and of linear imidates 32 (Nu = OR) or amides 32 (Nu = OH) from a-chloro-a-phenyl ketimines. ... 

Finally, several equilibrium and kinetic properties of aldehyde-bisulfite adducts were found to be linearly related Taft s a parameter (Betterton et al.t 1988). These compounds, which include a-hydroxymethane sulfonate and other a-hydroxyalkyl sulfonates, may be important reservoirs of S(IV) species inj clouds, fog, and rain. Fairly good relationships were found between equilibrium properties (e.g. acidity constants) and Sir values, but rates constants for) nucleophilic addition of S03 to the aldehydes showed only a crude fit, Similarly, poor results were found in applying a to hydrolysis reactions of] volatile alkyl chlorides (T. Vogel, University of Michigan, personal communh cation, 1989), and this has been shown to be a general characteristic of reactioni of alkyl halides with nucleophiles (Okamoto et al., 1967). 

Basically, the dediazoniation of diazoacetate (7.28) and diazoacetone (7.29) follows the same mechanism. The intermediate diazonium ions are not stable, but are steady state intermediates (ki < k- k- > ki)- McCauley and King (1952), Albery and Bell (1961), and Albery et al. (1968) found that the measured overall rate constants k of these dediazoniations are proportional to the acid strength in aqueous solution (Hammett acidity function Hq) reflecting the expected influence of acid on k, but the constants k also increase linearly with addition of salts of the acid used. The influence of these acid anions is a function of their nucleophilicity (Cl < Br- < I-). ... 

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