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Cleavage reactions solvolysis

Interstrand cross-links are unstable in conditions close to physiological conditions [57]. The bonds between platinum and the N(7) of guanine residues are cleaved spontaneously, with essentially one cleavage reaction per cross-linked duplex in either of both DNA strands (tl/2 for the cleavage reaction is about 29 h). As shown in the reaction scheme (Fig. 2), the cleavage generates monofunctional adducts which can react further to yield interstrand and intrastrand cross-links. The distorted local conformation could allow the formation of adducts which are not usually formed in double-stranded DNA containing a monofunctional adduct. An attractive hypothesis to explain the instability of the interstrand cross-links is that one of the two water molecules, in apical position with respect to the square of the platinum atom, labilises the G-Pt bond in solvolysis reaction. When the local... [Pg.164]

Solvolysis of benzyl arenesulphenates proceeds via S—O bond cleavage and is a second-order process, while benzyl trichloromethanesulphenates undergo first-order C—O bond cleavage on solvolysis. Formation of a sulphoxide from a benzyl trichloromethanesulphenate is one of two reaction paths resulting from ionization in polar media, the alternative to this ionization-recombination process being further dissociation into dichloro-sulphine (ClgCSO) and a benzyl chloride, ... [Pg.54]

Scheme 12.15 gives some examples of both acid-catalyzed and nucleophilic ring openings of epoxides. Entries 1 and 2 are cases in which epoxidation and solvolysis are carried out without isolation of the epoxide. Both cases also illustrate the preference for anti stereochemistry. The regioselectivity in Entry 3 is indicative of dominant bond cleavage in the TS. The reaction in Entry 4 was studied in a number of solvents. The product results from net syn addition as a result of phenonium ion participation. The ds-epoxide also gives mainly the syn product, presumably via isomerization to the... [Pg.1107]

Photosolvolysis of some vinyl iodonium substrates can be compared with thermal solvolysis of the same substrates. Photochemical reaction of (E)- and (Z)-2-phenylprop-l-enyl(phenyl)iodonium tetrafluoroborate (31) in methanol and TFE gave products of heterolytic cleavage of vinylic C-I bond as summarized in Table III (for the product structures see eq 14.17 In contrast to... [Pg.96]

The cycloaddition of aldehydes and ketones with ketene under the influence of quinine or quinidine produce chiral 2-oxetanones [46,47]. Solvolytic cleavage of the oxetanone, derived from chloral, and further solvolysis of the trichloromethyl group leads to (5)- and (R)-malic acids with a 98% ee [46] (the chirality of the product depends on the configuration of the catalyst at C-8 and, unlike other alkaloid-induced reactions, it is apparently independent of the presence of the hydroxyl group). No attempts have been made to catalyse the reaction with chiral ammonium salts. [Pg.529]

Results such as these have led to recurring discussions about the extent of stabihzation of the transition state for heterolytic cleavage at tertiary carbon by nucleophilic assistance from solvent. The difficulty lies in reconciling studies that suggest that there is a small dependence of obsd (s ) for solvolysis of tert-butyl chloride,and some cumyl derivatives, on solvent nucleophilicity with other work that shows there is no detectable stabilization of the transition state for these reactions by interaction with the strongly nucleophilic azide and hydroxide ions, and the strong neutral nucleophile propanethiol. ... [Pg.63]

Oxetanes are much less susceptible to cleavage by nucleophiles than oxiranes, except in the presence of acids. Several types of acid-catalyzed nucleophilic reactions are described in the previous section, such as reaction of hydrogen halides to give 3-halogeno-1-propanols and various acid-catalyzed solvolysis reactions. Another example of this type is the reaction of thiourea with 2-alkyloxetanes in the presence of hydrochloric or perchloric acid to give excellent yields of 3-alkyl-3-hydroxybutylisothiouronium salts (equation 39) <67CR(C)(264)1309>. [Pg.384]

The solvolysis of tetrabenzyl pyrophosphate catalyzed by lutidine (see above) is further catalyzed a thousandfold by calcium ions. In the presence of 0.02M calcium ion and 0.2M lutidine, the solvolysis of tetrabenzyl pyrophosphate (with cleavage of the P—O bond) is increased by a factor of the order of 1,COO,000 over the uncatalyzed reaction (63). The bivalent cation chelates with two oxygen atoms of the pyrophosphate ester, and the positive charge in the chelate greatly enhances the susceptibility of the phosphorus atom toward nucleophilic attack. [Pg.34]

The typical reactions of carbocation intermediates were discussed in Chapter 7. The solvolysis of alkyl halides is an example of the involvement of carbocations in the SnI mechanism, in other words, where the final outcome is a nucleophilic substitution. The first step is a heterolytic cleavage of the C—X bond. Properties of X which favor heterolytic cleavage, namely electronegativity difference with carbon (the larger, the better) and the degree of overlap of the X orbital with the spn orbital of carbon (the smaller the better), have already been elucidated (Chapter 4). The transition state has partial... [Pg.129]

Depending on the substituents, either elimination reactions or solvolysis leads to the product 36 or 37, respectively. The formation of addition product 37 can be explained by heterolytic cleavage under formation of a Co(III) complex and a carbanion, which is then protonated by the solvent. Owing to the carbanion-stabilizing ability of the cyano group this pathway is pronounced in the reaction with acrylonitrile. The product 39 is formed... [Pg.513]

This reaction is only of limited synthetic utility, and has mainly been used to verify that metallations had indeed taken place [1-3], or for the regioselective introduction of deuterium or tritium into a molecule. The solvolysis of silanes, organogermanium compounds, and phosphonium salts to yield alkanes with simultaneous cleavage from the support is discussed in Section 3.16. [Pg.169]

In certain cases, the silver ion assisted solvolysis fails to initiate electrocyclic reaction to give ring-expanded compounds, leading instead to a cleavage product (equation 90).227 The dichlorocarbene adduct (48) on FeCb-promoted cleavage in ether affords exclusively a-trichloromethylcyclohexanone, whereas in DMF a small amount of chlorocycloheptenone also was obtained (equation 91).228... [Pg.1019]


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See also in sourсe #XX -- [ Pg.346 ]




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Cleavage reaction

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