Cyclohexene peresters

An example of this reaction is the reaction of cyclohexene with t-butyl perbenzoate, which is mediated by Cu(I). " The initial step is the reductive cleavage of the perester. The t-butoxy radical then abstracts hydrogen from cyclohexene to give an allylic radical. The radical is oxidized by Cu(II) to the carbocation, which captures benzoate ion. The net effect is an allylic oxidation. 

Andrus also reported the synthesis and use of biphenyl-derived bis(oxazoline) (154) as a ligand for Cu(I) (110). In the presence of this catalyst, cyclohexene is oxidized in comparable yield and selectivity as 55c CuOTf complexes. The ni-trobenzoate perester was found to be a more reactive oxidant than perbenzoate, although the reaction still requires 5 days to proceed to completion, Eq. 93. 

Although the first example of an asymmetric Kharasch-Sosnovski reaction with a chiral perester was reported as early as 1965 [17], major advances have only been made in the last ten years. In the early 1990s, Muzart carefully reinvestigated earlier results obtained by Araki and Nagase [18]. After intensive optimization of the reaction conditions, the acyloxylation of cydopentene and cyclohexene gave products with up to 59 and 45 % ee, respectively. The best conditions for the oxidation of cyclohexene were found to involve the use of 5 mol% copper oxide, 10 mol% proline (1), and tert-butyl perbenzoate/benzoic acid in benzene under reflux (Scheme 2) [19]. 

Oxidative TVansformations. The use of 1 in enantioselective oxidations remains limited at the present time. Among the promising developments, allylic perester oxidation proceeds with significant enantioselection. The copper(I)-catalyzed oxidation of cyclohexene furnished the protected cyclic allylic alcohol with modest enantioselection (eq 3). ... 

The highest selectivities to date have been achieved using copper-bisoxazolines such as (5.119)-(5.121) in combination with ferf-butyl-p-nitrobenazoate (5.122). Cycloalkenes such as cyclopentene (5.123), cyclohexene (5.124) and cyclohep-tene (5.125) are particularly good substrates for this asymmetric transformation. Multiple equivalents of olefin are generally used and yields are based on the perester. 

The peresters (758 X = H, Ph, or Me) showed first-order kinetics on thermal decomposition in cyclohexene. Rate and activation data were indicative of a radical mechanism. Similarly, in the thermolysis of the peroxide (759) in carbon tetrachloride, the scrambling of oxygen in the products when 0-labelled peroxide was used indicated a radical cage mechanism. The products obtained on irradiation of the azaspriranes (760 n = 1 or 2) may be rationalized by homoallyl rearrangements of the intermediate spiro-radicals. ... 

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