Kharash addition

Another advantage of dendrimer-based catalysts concerns their easy recovery by stabilization at the surface of a polymer. The principal activities in dendritic catalysis lie in homogeneous catalysis, including Kharash addition of CC14 to methacrylate, palladium-catalyzed allylic alkylation, hydrogenation of olefins, hydroformylation, cyclopropanation, and oxidation.258 Dendrimers with redox-active cores have been proposed as promising materials for miniaturized information-storage circuits.259... 

Qc = [26.05 x N + c] kcal/mole where (N) is the number of electrons inter-displaced between C and O atoms and (c) correction factor, depending on the type of compound. These factors are given in Ref 4 and some additional data may be found in Ref 7. The value given earlier by Sventoslavsky was 26.12 kcal/mole, which is considered as being very close to that of Kharash (26.05)... 

The authors used (5)-carvotanacetone (dihydrocarvone) as starting material (Scheme 34). To prepare the linearly conjugated sUylenol ether, they used the Kharash protocol and attained y-alkylation by Mukaiyama aldol reaction with trimethylorthoformate (195). The ketoacetal 295 was a-hydroxylated according to Rubottom by silylenol ether formation followed by epoxidation and silyl migration. Acid treatment transformed 296 to the epimeric cyclic acetals 297 and 298. endo-Aceta 297 was equilibrated thereby increasing the amount of exo-acetal 298. The necessary unsaturated side chain for the prospected radical cyclization was introduced by 1,4-addition of a (trimethylsilyl)butynylcopper compound. 

Addition of the anion of 2-methyl-l,3-cyclopentadione (348) to protoane-monin (349), easily prepared from levulinic acid in four steps (207), led to adduct 350 in low yield due to ready self-condensation (Scheme 39). Transesterification with acidic methanol set the alcohol free, which cyclized spontaneously to the 1 1 mixture of ketals 351 and 352. To enhance the yield of the ketal 352, ketal 351 was recycled by equilibration in acidic methanol. Under Kharash-Grignard conditions, the isopropenyl group added unselectively in 1,4-mode and the ester enolate 353... 

Inspired by M. S. Kharash s work on radical addition of CCI4 to olefins [21], the same methodology was applied to perfluoroalkyl halides [13]. It was found that the addition of these compounds to olefins could be achieved with higher selectivity and at lower temperatures in the presence of radical initiators [22] (Scheme 2.101). 

Ruthenium complexes were among the first catalysts employed for controlled radical polymerization via ATRP mechanism (i, 2). One the one hand, this happened due to the fact that ATRP process originates from Kharash reaction of radical addition (5), which is catalyzed by complexes of this metal. On the other hand, this was associated with the unical properties of ruthenium atom, particularly the ability to assume different oxidation states and various coordination geometries 4-6). 

Kharash MS, Urry WH, Kudmia BM (1948) Reactions of atom and free radicals in solution. XX. The addition of aldehydes to olefins. J Org Chem 13 248-253... 

The mechanism of the Cu(I)-mediated Kharash-type addition of CCI4 to allyl chloride using copper-triphenylphosphine complexes has been studied. Several features of note were found, including an abnormally low rate for the reactions and the observation of an induction period. A mechanism that involves an initial formation of a catalytic Cu(I)-olefin complex was proposed. ... 

Cuprates have been used in organic synthesis since Kharash, in 1941, observed the catalysis by cuprous ions in the 1,4 addition of Grignard reagents on enones. Cuprates allow the alkylation of alkyl halides, carbonyl groups, nitriles, epoxides and enones (see Chap. 21.3.1). 

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