Peroxycarboxylic acids hydrogen bonding

Similarly to peroxycarboxylic acids, DMDO is subject to cis or syn stereoselectivity by hydroxy and other hydrogen-bonding functional groups.93 However a study of several substituted cyclohexenes in CH3CN —H20 suggested a dominance by steric effects. In particular, the hydroxy groups in cyclohex-2-enol and... 

Solvent effects in the peroxycarboxylic acid epoxidations are significant. The epoxidation rates in ether or ethyl acetate are approximately one-tenth of those in benzene or chloroform. The much slower epoxidation with peroxycarboxylic acids with intermolecular hydrogen bonding is indicative of the development of a cyclic transition state. 

The most widely used and, presumably, the most chemoselective reagents for the epoxidation of nucleophilic C—C double bonds are the peroxycarboxylic acids (see Houben-Weyl, Vol. IV/ 1 a, p 184, Vol. Vl/3, p 385, Vol. E13/2, p 1258). Using chloroform as solvent, epoxidation rates are particularly high79. Reactive or acid/base sensitive epoxides can often be obtained with dimethyldioxirane (see Houben-Weyl, Vol. R13/2, p 1256 and references 15, 16, 87-90), peracid imides (see Houben-Weyl, Vol. IV/1 a, p 205, Vol. VI/3, p 401, Vol. E13/2, p 1276) (prepared in situ from nitriles and hydrogen peroxide), hydroperoxy acetals (see Houben-Weyl, Vol. El3/2, p 1253) or peroxycarbonic acid derivatives (see Houben-Weyl, Vol. IV/la, p 209 and references 17-19) as oxidants. For less reactive alkenes, potassium hydrogen persulfate is a readily available reagent for direct epoxidation20. 

The epoxidation of simple alkenes with peroxycarboxylic acids involves an electrophilic attack of peracid with the formation of a bicyclic or a mono-cyclic transition state (Scheme 6.1), as first proposed by Bartlett [7] or recently suggested by theoretical studies [8] respectively. The reaction takes place readily in nonpolar solvents such as dichloromethane (DCM) and benzene and one can argue that hydrogen-bonding solvents, in particular, should retard the rate by interfering with intramolecular hydrogen bonding... 

---