Compound solvolyzing

Ionization of either the exo (XXVI) or the endo (XXVII) derivative leads to substitution products with the exo configuration. The endo compounds solvolyze slowly, about like cyclohexyl derivatives, while the exo derivatives solvolyze as much as 350 times faster, indicating participation by neighboring carbon. Furthermore, optically active exo starting material gives racemic exo product. All of these results are consistent with the formation of the symmetrical ion XXVIII, in which carbon atoms 1 and 2 are indistinguishable.287 288 But the ion XXVIII... 

A much more spectacular driving force was found in the acetolysis of anti-1-norbornenyl tosylate (51). This compound solvolyzes 1011 times faster than the saturated analog and gives as the sole product the anti-acetate, 52.68 Winstein attributed the enormously accelerated rate to powerful anchimeric assistance of both p orbitals of the 2,3-double bond. 

That maximum acceleration occurs when the vacant p orbital is parallel to the plane of the cyclopropyl ring can be seen from the solvolysis of spiro[cyclo-propane-l,2 -adamantyl] chloride (71). The carbocation formed by departure of Cl is unable to adopt the geometry of the bisected cyclopropylcarbinyl cation, but can orient its empty p orbital properly to form the bicyclobutonium ion. This compound solvolyzes 103 times more slowly than 1-adamantyl chloride.82 On the other hand, 72 solvolyzes 10s times faster than 73. The cation from 72 does have its p orbital parallel to the plane of the ring as in the bisected cyclopropylcarbinyl cation.83... 

Hazen has compared the reactivity of acetals to simple co-methoxy alkyl sulfonates. Some of his results are shown in Table 9. As expected, all the methoxy-containing compounds solvolyze much faster than the model substrate (139). Because of differences in the nucleophilicity of the solvents, only the solvolyses in trifluoroethanol occur with Fk = 100% (calculated from kinetic data). The kinetic results show that a simple methoxy group is about 40% better than the acetal group in MeO-6 participation [e.g., compare (141) versus (34), Table 9]. Consistent with the results of Win-stein et al. vide supra), MeO-5 participation in acetals is more effective than MeO-6 participation. While solvolysis of (34) in buffered... 

The most general methods for the syntheses of 1,2-difunctional molecules are based on the oxidation of carbon-carbon multiple bonds (p. 117) and the opening of oxiranes by hetero atoms (p. 123fl.). There exist, however, also a few useful reactions in which an a - and a d -synthon or two r -synthons are combined. The classical polar reaction is the addition of cyanide anion to carbonyl groups, which leads to a-hydroxynitriles (cyanohydrins). It is used, for example, in Strecker s synthesis of amino acids and in the homologization of monosaccharides. The ff-hydroxy group of a nitrile can be easily substituted by various nucleophiles, the nitrile can be solvolyzed or reduced. Therefore a large variety of terminal difunctional molecules with one additional carbon atom can be made. Equally versatile are a-methylsulfinyl ketones (H.G. Hauthal, 1971 T. Durst, 1979 O. DeLucchi, 1991), which are available from acid chlorides or esters and the dimsyl anion. Carbanions of these compounds can also be used for the synthesis of 1,4-dicarbonyl compounds (p. 65f.). 

Figure 7-2 indicates that this intramolecular assistance takes place with those compounds having substituents to the right of X = OMe = —0.78), for in this portion of the a scale compounds 8 solvolyze more rapidly than do 7. At the X = OMe member, however, the two series have essentially identical reactivities, and this behavior continues at more negative cr. It. therefore, appears that intramolecular participation by the double bond occurs when it is needed when the X substituent is sufficiently electron-donating to stabilize the cation, intramolecular assistance is not needed, so it does not occur, and the saturated and unsaturated series show the same reactivity. 

The compound 2-octyl brosylate was labeled at the sulfone oxygen with 0 and solvolyzed. The unreacted brosylate recovered at various stages of solvolysis had the 0 considerably, though not completely, scrambled ... 

Phenylmethylsilanediol can also be prepared by solvolysis of PhMe-SiH2 [Eq. (11)] and the para-disubstituted arene p-(HMe2Si)2C6H4 is also solvolyzed to give the corresponding compound containing two Si-OH groups (34). 

Oxidation of arylolefins, enolethers, or dienes yields intermolecular homocoupling products in moderate to good yield (see Sect. 13.2.1.4) however, no pronounced diastereoselectivity was observed. This is also due to the fact that the coupling sites do not tolerate substituents that would make up a prostereogenic center. Furthermore, the fairly stable cations of the dimerized radical cation solvolyze stereounselectively. The same holds for the intermolecular coupling of aromatic compounds, in... 

The gold compound AuC1(PC13) also forms stable solvolysis products from alcohols however, reduction occurs in water (2, 51). Surprisingly, it has been reported that the iridium compound IrCl3(PCl3)3 does not solvolyze in alcohols (35,70). 

If the reaction is performed on two molecules that differ only in the leaving group (for example, /-BuCl and /-BuSMe ), the rates should obviously be different, since they depend on the ionizing ability of the molecule. However, once the carbocation is formed, if the solvent and the temperature are the same, it should suffer the same fate in both cases, since the nature of the leaving group does not affect the second step. This means that the ratio of elimination to substitution should be the same. The compounds mentioned in the example were solvolyzed at 65.3°C in 80% aqueous ethanol with the following results 11... 

Benzo fused rings containing two or more electron-donating heteroatoms along with the boron atom, e.g. (57), are more stable to hydrolysis and alcoholysis than the corresponding open-chain derivatives, yet they are more or less sensitive to nucleophilic breakdown. For example, compound (77) is solvolyzed within five days in alcoholic solution at room... 

The work on the cholesterol system stimulated investigation of other examples of homoallylic participation. Roberts found that exo-5- and endo-5-bicyclo[2.2.1]heptenyl (i.e., exo-5- and enrfo-5-norbornenyl) halides (47 and 48) both solvolyze in aqueous ethanol to give the same product (49) the exo compound (47) solvolyzes about ten times more rapidly than the endo compound (48). Roberts pointed out that backside homoallylic participation in ionization was possible in 47 but not in 48 (see Figure 6.6). Once 48 has ionized it can, in a second... 

Double bonds further removed from the incipient carbocation than the homoallylic position can also assist, in jonizatien-if the..geometry of the system. allows Tt. For example -nitrobenzoate (59) solvolyzes 1500 times faster than the corresponding saturated compound in aqueous acetone. The product is trans,trans-1 -decalol (60). If after 12 half-lives the product is iso-... 

A set of rapidly equilibrating carbenium ions might account for the rearrangements and the label scrambling but this cannot be the correct explanation, for cyclopropylcarbinyl, cyclobutyl, and allylcarbinyl systems all solvolyze much more rapidly than would be expected from model compounds. Thus, for example, the rate of solvolysis of cyclopropylcarbinyl tosylate is 10 times that of the solvent-assisted solvolysis of isobutyl tosylate.77 Cyclobutyl tosylate solvolyzes 11 times... 

The exo compound actually solvolyzes 5.7 times faster than the endo compound. Since there is no obvious route for a bond participation here, it appears that there must be an increase in nonbonded strain in the transition state of 87 of R 7Tn 5.7 or 1 kcal mole-1.106... 

The primary adduct 53 (Eq. (117) ) of the anodically generated radical R undergoes a series of follow-up reactions a) hydrogen abstraction to 54, b) dimerization to additive dimers 55, c) coupling with R to 1,2-disubsti-tuted monomers56, d) le-oxidation to a carbonium ion that either solvolyzes to 57 or, when 1,3-dicarbonyl compounds are added cyclizes intramolecularly to tetra (58) - or dihydrofuran derivatives (59). Product control is possible in some cases by suitable choice of the anode potential. With a high anode potential,... 

In fact, in the absence of a-substituents that would be able to delocalize the positive charge, vinyl compounds are extremely unreactive. This is illustrated by the observation (Kaufman and Miller, 1969) that /3-bromostyrene (119), in the presence of silver nitrate, does not solvolyze... 

The solvolysis reactions of cis and tram f-butylcyclohexyl tosylates also have been studied in NMA238. In both cases the primary product was 4-f-butylcyclohexene (no other cyclohexene products were detected) and much smaller quantities of cyclohexyl acetates and cyclohexanols were also recovered. The reaction rate was first order with respect to the tosylates. Similar to results of studies of the reaction in other solvents, the c/s-tosylate was solvolyzed more readily than was the tram compound. The stereochemical distribution of the minor products was significantly altered by small amounts of water (<1%) added to the NMA solvent. 

The compounds are solvolyzed some 104 times faster than benzyl chloride in methanol. Hence, the furan, thiophene, and selenophene rings are more efficient than the phenyl at stabilizing a positive charge at an a carbon. 

The hydrogen cyanide complex,28 [HC=NXeF] [AsF6], is made by interaction of XeF+ or Xe2F cations with HCN in anhydrous HF. The cation is linear with a weak Xe—N bond and solutions in HF are extensively solvolyzed to give XeF2 and HC=NH+. [C6FsXe][AsF6] has been shown to form compounds with pyridine and substituted pyridines.29... 

A great majority of organometallic compounds, especially of those which can be used as initiators, are easily solvolyzed by polar molecules. Inactive or weakly active products are formed. If the properties of the metal-carbon bond are to be useful for initiating anionic polymerizations, the organometallic compound must be able to yield a carbanion, either free or bound to the counter ion. 

Solvolyzing compounds do not, of course, react selectively only with the transition metal compounds. They also attack the organometal by breaking the alkyl—metal bond. Thus their effect is similar to that of the former case, and the effects are additive. 

Di(silyl)benzene gives the di(chlorosilyl)benzene reagent upon treatment with boron trichloride (Scheme 3). Contrary to the parent compound, this derivative is readily solvolyzed and gives cyclic siloxanes, silthianes, silazanes and silylphosphines on contact with water, hydrogensulfide, ammonia, amines, or phosphines, respectively. 

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