Mechanistic investigations, asymmetric alkylation

In this review, we focus mainly on the preparative utility of organic peroxides, and only few mechanistic investigations are discussed. This review covers synthetic methodologies for the preparation of alkyl hydroperoxides and dialkyl peroxides (Section II) and the synthetic use of these peroxides in organic chemistry (Section III). In Section II, general methods for the synthesis of organic hydroperoxides and dialkyl peroxides are discussed, as well as the preparation of enantiomerically pure chiral hydroperoxides. The latter have attracted considerable interest for asymmetric oxidation reactions during the last years. 

Although mechanistically different, a successful kinetic resolution of cyclic allyl ethers has recently been achieved by zirconium catalysis [2201. Other metals such as cobalt [221], ruthenium [222], and iron [2231 have been shown to catalyze allylic alkylation reactions via metal-allyl complexes. However, their catalytic systems have not been thoroughly investigated, and the corresponding asymmetric catalytic processes have not been forthcoming. Nevertheless, increasing interest in the use of alternative metals for asymmetric alkylation will undoubtedly promote further research in this area. 

The mechanistic pathway for these asymmetric alkylations and the configurational stability of the chiral lithioformamidines have been investigated. A limitation of this strategy is that saturated, cyclic, secondary amines (e.g., pyrrolidines and piperidines) cannot be successfully alkylated in an asymmetric fashion. 

The asymmetric hydroxylation of enals has been achieved using a resolved A -heterocyclic carbene catalyst (Scheme 2.9) [11]. The chemistry was carried out under very mild conditions using 4-nitropyridine Af-oxide as the oxidant and was highly selective (up to 92% ee). An array of enals bearing a range of alkyl and aryl groups was successfully functionahzed in this work. The authors proposed a radical pathway for the chemistry based upon a series of mechanistic investigations. 

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