Addition reaction inverse

Convincing evidence for oxidative addition by inversion has been presented by the reaction of chiral (5)-( )-3-acetoxy-l-phenyl-1-butene (4) with Pd(0)(dppe), followed by the treatment with NaBF4 to give optically active the TT-allylpalladium complex (l/ ,25,35) 5 with 81% stereoselectivity[19]. 

Walden, Paul, 360 Walden inversion. 359-360 Wang resin, solid-phase peptide synthesis and. 1037 Water, acid-base behavior of, 50 dipole moment of, 39 electrostatic potential map of. 53 nucleophilic addition reactions of, 705-706 pKaof, 51-52... 

Addition reactions with alkenes to form cyclopropanes are the most studied reactions of carbenes, both from the point of view of understanding mechanisms and for synthetic applications. A concerted mechanism is possible for singlet carbenes. As a result, the stereochemistry present in the alkene is retained in the cyclopropane. With triplet carbenes, an intermediate 1,3-diradical is involved. Closure to cyclopropane requires spin inversion. The rate of spin inversion is slow relative to rotation about single bonds, so mixtures of the two possible stereoisomers are obtained from either alkene stereoisomer. 

The chain length is therefore adversely afFected by the irradiation dose rate being inversely proportional to its square root. Wagner (1969) lists a large class of unsaturated compounds in which addition reactions can be induced by irradiation. Typical examples involving long chain lengths are for the addends HC1, Cl2, and HBr in ethylene, benzene, toluene, and so on. where the products are telomers or hexachlorides. 

The monomer reactivity ratios for many of the most common monomers in radical copolymerization are shown in Table 6-2. These data are useful for a study of the relation between structure and reactivity in radical addition reactions. The reactivity of a monomer toward a radical depends on the reactivities of both the monomer and the radical. The relative reactivities of monomers and their corresponding radicals can be obtained from an analysis of the monomer reactivity ratios [Walling, 1957]. The reactivity of a monomer can be seen by considering the inverse of the monomer reactivity ratio (1 jf). The inverse of the monomer reactivity ratio gives the ratio of the rate of reaction of a radical with another monomer to its rate of reaction with its own monomer... 

Cycloaddition of diphenyl ketene with benzoquinone diimides (44) gives quinoxalinones of type 45.45 Analogous additions of olefins lead to tetrahydroquinoxalines these reactions are classified as Diels-Alder additions with inverse electronic demand. 

There is a striking similarity in the behavior attributed to the triplet biradicals believed to be formed in the reactions of both triplet methylene and triplet oxygen with the 2-butenes. It should also be pointed out that in the triplet addition reactions of methylene, cis and trans olefins do not give the same cis and trans product ratios, indicating that the rate of spin inversion necessary for closure in the biradical intermediate occurs at a rate comparable to the rate of rotation about C—C bonds. 

In a closely related reaction the thioketene complex 106210 was reduced by sequential addition of H and H+ to give the thioketone complex 107. However, compared to the reaction of 104 the sequence of H+ and H addition is inverse. Complex 107 is coordinatively unsaturated and therefore added PPh3 rapidly (Scheme 25).109... 

Electrophilic addition reactions of tetravalent tellurium compounds have been reviewed.64 2-Naph-thyltellurium trichloride (ArTeCb) adds to alkenes in an anti stereospecific manner (equation 11), whereas tellurium tetrachloride gives mixtures of 2 1 adducts with both syn and anti addition.72 A one-pot alkene inversion procedure has been developed, based upon TeCU addition to alkenes followed by treatment of the (3-chloroalkyltellurium trichloride adduct with aqueous Na2S (Scheme 37).73 Tellurium compounds such as tellurinyl acetates, ArTe(0)0Ac, prepared in situ through reaction of tellurinic acid anhydrides with acetic acid, can be employed in oxytelluration and aminotelluration procedures (Schemes 38 and 39).74 In the oxytelluration reaction intermediate triacetates of the type RCH2Te(OAc)2Ph are reduced with hydrazine to the corresponding tellurides. 

Similar high diastereoselectivities are observed for the addition reaction of t-butyl alcohol to (E)- and (Z)-1628. High diastereoselectivities are also observed for the reaction with ethanol at low concentration, but the selectivity decreases rather sharply by increasing the ethanol concentration. The diastereoselectivities for the reaction of ethanol, i.e. the [syn /[anti product ratios, are linearly and inversely correlated with the concentration of the alcohol ... 

One possible explanation is offered by the results of a recent laboratory study (21) which showed that the mechanism of the DMS oxidation by OH is a function of temperature and that the OH addition mechanism dominates over H abstraction at temperatures below 285 K. Hynes et al. (21) speculated that OH addition to DMS may lead primarily to the formation of MSA and that the yield of MSA may increase inversely with temperature. Temperatures during our flights were around + 12°C at ground level and decreased to about -23°C at the highest flight altitude. If MSA is indeed the dominant product of the OH addition reaction we may calculate a corresponding increase of the MSA yield from 50% to 76%, respectively, based on tne data of Hynes et al. (21). The... 

The dependence of the rate upon the inverse of the hydrogen ion concentration (base-catalysis) is reasonably attributed to the necessity for the coordinated water molecule to lose a proton. The resulting ethyl-ene-hydroxypalladium species (the cis isomer), I, is then believed to undergo an internal addition reaction of the hydroxyl group to the coordinated ethylene to form the dichloro-2-hydroxyethylpalladium anion, II. The final step is a decomposition of the last compound into acetaldehyde, palladium metal, hydrogen ion and chloride anions. 

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