Cramer reaction

F. Hansske and F. Cramer, Reaction of the ribose moiety of adenosine and AMP with periodate and 5,5-dimethylcyclohexane-l,3-dione (dimedone), Carbohydr. Res., 41 (1975) 366-369. P. N. Lowe and B. R. Beechey, Preparation, structure, and properties of periodate-oxidised ATP, a potential affinity-labelling reagent, Bioorg. Chem., 11 (1982) 55-71. 

With the realization that the cycloamyloses form stable monomolecular inclusion complexes in solution came the idea that the inclusion process might affect the reactivity of an organic substrate. This idea was initially pursued by Cramer and Dietsche (1959b) who discovered that the rates of hydrolysis of several mandelic acid esters are enhanced by the cycloamyloses. More recently, the inclusion process has been shown to exert both accelerating and decelerating effects on the rates of a variety of organic reactions. The remainder of this article will be devoted to a discussion of these reactions in an attempt to review, compare, and unify the many intriguing facets of cycloamylose catalysis. 

Noting that the reaction of cycloheptaamylose with diphenyl pyrophosphate produces equal amounts of phenol, monophenyl phosphate, and phosphorylated cycloheptaamylose, Hennrich and Cramer (1965) proposed a nucleophilic mechanism (Scheme IV). According to this mechanism, a rapid, reversible association of the pyrophosphate with cycloheptaamylose... 

The observed first-order appearance of two moles of phenol in the reactions of cycloheptaamylose with the methylphosphonates is of particular interest. This may be explained, as illustrated in Scheme VI, by an intramolecular displacement, within the covalent intermediate, of the second mole of phenol by an adjacent cycloamylose hydroxyl group. Presumably, both the methylphosphonates and the carbonates proceed by this pathway which is similar to the mechanism proposed by Hennrich and Cramer (1965) for the reactions of the cycloamyloses with diaryl pyrophosphates. 

The X-ray structure of 37 confirms the interligand C—C coupling. Cramer et al. have reported a coupling reaction that is believed to be quite similar to Eq. (8) using an organouranium complex [Eq. (10)] (47). The... 

This preferential formation of 1 1 adduct to form 1,4-hexadiene in a mixture of ethylene and butadiene was further studied by Cramer (4). He concluded that the results appeared to be the consequence of thermodynamic control reactions through a relatively stable 7r-crotyl Rh complex. 

The most general and comprehensive reaction mechanism of the 1 1 codimerization has been reported by Cramer (4). The results were based on reaction properties measured in an alcoholic medium under relatively mild conditions. 

The rate also varies with butadiene concentration. However, the order of the rate dependence on butadiene concentration is temperature-de-pendent, i.e., a fractional order (0.34) at 30°C and first-order at 50°C (Tables II and III). Cramer s (4, 7) explanation for this temperature effect on the kinetics is that, at 50°C, the insertion reaction to form 4 from 3, although still slow, is no longer rate-determining. Rather, the rate-determining step is the conversion of the hexyl species in 4 into 1,4-hexadiene or the release of hexadiene from the catalyst complex. This interaction involves a hydride transfer from the hexyl ligand to a coordinated butadiene. This transfer should be fast, as indicated by some earlier studies of Rh-catalyzed olefin isomerization reactions (8). The slow release of the hexadiene is therefore attributed to the low concentration of butadiene. Thus, Scheme 2 can be expanded to include complex 6, as shown in Scheme 3. The rate of release of hexadiene depends on the concentra-... 

In the codimerization reaction, both reactants are present in large excess compared to the catalyst concentration. The selectivity toward a 1 1 codimerization to form 1,4-hexadiene, instead of a random oligomerization, represents a rather unique reaction, especially in view of the fact that the same catalyst also dimerizes ethylene to butene (3) at about the same rate as the codimerization. The explanation forwarded by Cramer (4, 7) is based on the overwhelmingly favored stability of the tt-... 

The effect of donors on the catalyst activity can be explained by assuming that the dimeric complex is not an active catalyst (Cramer s kinetics indicate a monomeric Rh species as active catalyst see Section II,B,2) and that 14 with a free coordination site for ethylene is the active catalyst, while 15 with both coordination sites occupied by donors is catalytically inactive. When D is a weak donor, such as ketone or ether (see Fig. 5d), the reaction rate increases, slowly reaching a maximum and leveling off at the maximum as the concentration of the donor is increased. It can be speculated that these donors interact with the catalyst only to the extent that they break up the dimer 8 to form 14, but that... 

The generalized Bom model (GBM) can be regarded as a special case of the preceding procedures the reaction field is expressed in terms of a multi-center monopole representation of the solute molecule, using the Bom formula, Eq. (32).l3 ,6, 3 "5 The centers are the atomic nuclei. The results are quite sensitive to the method used to calculate the atomic charges Cramer and Truhlar, who have applied the GBM approach extensively13,16,107 use their Class IV charges for this purpose.16,107,116 Various techniques have been utilized to determine the radii.16,95,101,107... 

There have been numerous applications of continuum models to equilibria and reactions in solution surveys of these and extensive listings are provided by Cramer and Truhlar.16 Other studies have focused upon the effects of solvents upon solute molecular properties, such as electronic and vibrational spectra,16 dipole moments, nuclear quadrupole and spin-spin coupling constants and circular dichroism.12... 

Nucleophilic addition of phenolic nucleophiles to l,l-dicyano-2-arylethenes in the gas phase and in water has been studied theoretically" using the semiempirical AMI method and the Cramer-Truhlar solvation model SM2.1. The difference between the Brpnsted coefficients (a" = 0.81 and P" =0.65) determined for the gas-phase reaction is indicative of a small positive transition state imbalance of / = 0.16. For reaction in water the estimates (a" = 0.61 and P" = 0.36, giving I = 0.25) are close to the experimental values (a" = 0.55 and P" = 0.35) obtained with amine bases, and the small imbalance is as expected for a reaction involving no hybridization change at the incipient carbanion site. 

The first mechanism appears to be the better basis for describing most of the results referred to by Cramer (56). It will, however, be noted that the addition-elimination mechanism requires that the metal catalyst be supplied as a metal hydride. Where the catalyst has not been supplied in this form, the reaction has usually been carried out in the presence of reagents known to convert transition metal compounds to hydrides (e.g. protonic acids, alcohols or hydrogen). These substances are known as co-catalysts and, where they have been used, induction periods have been encountered which are consistent with hydride formation as required in mechanism (a), but which would not be expected for (b). 

Previous methods for the preparation of salts of geranyl diphosphate and other allylic isoprenoid diphosphates are based on condensation between the alcohol and inorganic phosphate by trichloroacetonitrile as originally reported by Cramer and modified by Popjak The reaction generates a complex mixture of organic and inorganic polyphosphates which must be separated by chromatography. The desired diphosphate ester has been prepared on small... 

Falvey examined the reactions of A-methyl-A-phenylnitrenium ion 65 (Fig. 13.37) in the presence and absence of chloride. It was found the yield of aniline (resulting from hydrolysis of the product iminium ion) was unaffected by added base. This finding ruled out a deprotonation process and led to the conclusion that a 1,2-hydride shift had occurred. Cramer et al. modeled this process using ab initio methods. 

An interesting route to 98 was suggested by Cramer et al. " cyclization of isonitrile 110 could lead to 98 in a rearrangement analogous to the Bergman cyclization. The activation enthalpy for the only slightly exothermic reaction was estimated at 18 kcal/mol. However, this novel access to m-arynes could not be realized experimentally so far. 

Taylor in 1925 demonstrated that hydrogen atoms generated by the mercury sensitized photodecomposition of hydrogen gas add to ethylene to form ethyl radicals, which were proposed to react with H2 to give the observed ethane and another hydrogen atom. Evidence that polymerization could occur by free radical reactions was found by Taylor and Jones in 1930, by the observation that ethyl radicals formed by the gas phase pyrolysis of diethylmercury or tetraethyllead initiated the polymerization of ethylene, and this process was extended to the solution phase by Cramer. The mechanism of equation (37) (with participation by a third body) was presented for the reaction, - which is in accord with current views, and the mechanism of equation (38) was shown for disproportionation. Staudinger in 1932 wrote a mechanism for free radical polymerization of styrene,but just as did Rice and Rice (equation 32), showed the radical attack on the most substituted carbon (anti-Markovnikov attack). The correct orientation was shown by Flory in 1937. In 1935, O.K. Rice and Sickman reported that ethylene polymerization was also induced by methyl radicals generated from thermolysis of azomethane. 

Continuum models are the most efficient way to include condensed-phase effects into quantum-mechanical calculations, and this is typically accomplished by using the self-consistent reaction field (SCRF) approach for the electrostatic component. Therefore it is very common to replace the quantal problem by a classical one in which the electronic energy plus the coulombic interactions of the nuclei, taken together, are modeled by a classical force field—this approach usually called molecular mechanics (MM) (Cramer and Truhlar, 1996). 

An important feature of the cyclodextrins is that they can also accelerate chemical reactions, and therefore serve as models for the catalytic as well as the binding properties of enzymes. The rapid reaction is not catalysis, since the dextrin enters reaction but is not regenerated presumably it arises from approximation, where complex formation forces the substrate and the cyclodextrin into intimate contact. In particular, cyclodextrins can increase the rate of cleavage of phenyl pyrophosphate by factors of as much as 100 (Cramer, 1961). More recent work has improved upon this early example. 

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