Fragmentation heterolytic

Attempts at 4-exo nucleophilic cyclization failed, presumably because of a heterolytic fragmentation of the intermediate radical cation (Scheme 32) [139], not unlike that proposed (Scheme 15) for the decomposition of a mannose-derived alkene radical cation. 

The kinetics of the reaction of 2 -deoxyuridin-L-yl radicals (11) with thiols, with superoxide release from the peroxyl radical (13) generated, have been reported. Radical (11) is produced by photolysis of precursor (10). When the radical is produced in the presence of thiols, (12) is formed. Second-order kinetics were found for the reactions with thiols. Peroxyl radical (13) is formed in the presence of oxygen. This undergoes heterolytic fragmentation to the superoxide anion O2 and cation (14), which ultimately leads to 2-deoxyribonolactone (15). 

In cases where the substituent is a halide, the initial adduct is particularly reactive. For example, trapping of N-(4-chlorophenyl)-N-methylnitrenium ion 77 with methanol gives a variety of products (79-81). These result from various homolytic and heterolytic fragmentations of the intermediate 78. (Fig. 13.43). 

NMOPh was lO" times faster than the heterolytic fragmentation of... 

The Formation of Unsaturated Groups by Heterolytic Fragmentation , K. B. Becker and C. A. Grob, in Chemistry of Double-Bonded Functional Groups , ed. S. Patai, Wiley, New York, 1977, vol. 2, pp. 653-723. 

Mechanism and Stereochemistry of Heterolytic Fragmentation C. A. Grob, Angew. Chem., Int. Ed. Engl., 1969, 8, 535-546. 

Water Elimination, Heterolytic ((-Fragmentation and Formation of Radical Cations... 

A possible reaction course comes to mind. The A-vinyl-2-pyrrolidone also possesses at the oxygen a nucleophilic center which could attack the electrophilic carbene carbon and could release the carbene ligand from the metal. The intermediate product formed—irrespective of whether it is an open chain or a six-membered ring—then undergoes a heterolytic fragmentation by splitting similar to that observed by Grob (84) (Fig. 7). 

Helerolytic fragmentation of 1. -Mianyl tosylates. Marshall and Belletirc have shown (hat a 1,3-dithiane anion can participate in a heterolytic fragmentation reaction. Thus condensation of the aldehyde (1) with 1,3-propanedi thiol gives the 1,3-dithiane (2),... 

In reactions of this type, the direction of the electron flow between the radical X and the substrate molecule S depends, of course, on the oxidizing or reducing properties of X and the ability of S either to donate or to accept an electron. Irrespective of electron flow direction, transfer between X and S can proceed by the outer-sphere mechanism [37], Eq. 2, or by inner-sphere or bonded paths (Eqs 3 and 4) [38, 39]. The stoichiometry in Eqs 3 and 4 is the same as in Eq. 2. In the bonded mechanism, however, a heterolytic fragmentation of the bond joining X and S is the step in which the electron transfer actually occurs ... 

A dramatic increase in reactivity is observed on going from l and 2 (Tables 15 and 16, respectively) to 4, indicating that the presence of an electron withdrawing substituent on the y5-carbon strongly stabilizes the incipient negative charge which develops on this atom in the transition state for heterolytic fragmentation. 

The great utility of fragmentations, especially those of 1,3-diol monosulfonates, for the construction of functionalized, medium-sized cycloalkenes was developed by Wharton, by applying previous results. In recognition of his important contributions to the chemistry of heterolytic fragmentations of cyclic 1,3-diol derivatives, this reaction type has been referred to in a recent review as the Wharton fragmentation . ... 

The Wharton fragmentation was used as a key step in an approach toward the total synthesis of xenicanes by H. Pfander et al. ° Two optically active substituted frans-cyclononenes were synthesized starting from (-)-Hajos-Parrish ketone. First, the bicyclic 1,3-diol was protected regioselectively on the less sterically hindered hydroxyl group with p-toluenesulfonyl chloride in quantitative yield. Next, the monosulfonate ester was exposed to dimsylsodium in DMSO, which is a strong base, to initiate the desired heterolytic fragmentation. 

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