Bonds dioxirane oxygen insertion

C-H bond dioxirane oxygen insertion, 1138 dioxirane oxyfunctionahzation, 1136, 1138 oxidation, 531... 

T-bonds, C-H dioxirane oxygen insertion, 1138-9, 1158-63 trarw-Sabinene, synthesis, 891... 

Because C-H bonds are usually less reactive towards dioxirane oxidation than heteroatoms and C-C multiple bonds, it is instructive to give a few general guidelines on the compatibility of functional groups within the substrate to be submitted to oxidative C-H insertion Substances with low-valent heteroatoms (N, P, S, Se, I, etc.), C-C multiple bonds, and C=X groups (where X is a N or S heteroatom) are normally not suitable for C-H insertions, because these functionalities react preferably. Even heteroarenes are more susceptible to dioxirane oxidation than C-H bonds, whereas electron-rich and polycyclic arenes are only moderately tolerant, but electron-poor arenes usually resist oxidation by dioxiranes. N-oxides and N-oxyl radicals are not compatible because they catalyze the decomposition of the dioxirane. Oxygen insertion into Si-H bonds by dioxirane is more facile than into C-H bonds and, therefore, silanes are not compatible. Substance classes normally resistant towards dioxirane oxidation include the carboxylic acids and their derivatives (anhydrides, esters, amides, and nitriles), sulfonic acids and their de-... 

The enhanced propensity of dioxiranes to insert oxygen into unactivated alkane C—H bonds was ascribed initially to the high ring strain energy (SE) of dioxiranes that has sometimes exceeded 30 kcalmol" . Since the SE of these three-membered peroxides has recently been substantially reduced (SE = ca 11-18 kcalmoU ), a different explanation is required . 

Direct insertion into an X—H a bond constitutes the highlight of dioxirane chemistry . Besides the insertion of a dioxirane oxygen atom into an alkane acH bond, for practical purposes a most valuable oxyfunctionalization, also the more facile insertion into the asiH bond is known, a convenient and chemoselective method of preparing silanols. 

The chemical reactivity most associated with dioxiranes is the electrophilic transfer of oxygen to electron-rich substrates (e.g., epoxidation, N-oxidation) as well as oxygen insertion reactions into unactivated C-H bonds. The reactivity-selectivity relationships among these types of reactions has been examined in depth by Curci. The reaction kinetics are dependent upon a variety of factors, including electron-donor power of the substrate, electrophilicity of the dioxirane, and steric influences (95PAC811]. 

The same authors published a detailed report on the calculations of the oxygen insertion into unactivated C-H bonds by dioxiranes using DFT theory and on comparison of the transition structures for stepwise routes via radical pairs with the concerted pathway <2003JOC811>. The articles dealing with the mechanism of OH formation from ozonolysis of isoprene and a- and /3-pinene provide DFT and ab initio calculation results also for the dioxirane formation <2001CPL(358)171, 2002JA2692, 2005JCP114308>. 

W. Adam, R. Curci, L. D Accolti, A. Dinoi, C. Fusco, F. Gasparrini, R. Kluge, R. Paredes, M. Schulz, A. K. Smerz, L. A. Veloza, S. Weinkdtz, R. Winde, Epoxidation and oxygen insertion into alkane CH bonds by dioxirane do not involve detectable radical pathways, Chem. Eur. J. 3 (1997) 105. 

Oxyfunctionalization. Oxygen insertion into unactivated secondary and tertiary C-H bonds of protonated alkylamines can be very efficient with this dioxirane. Hydrogen bonding between the dioxirane and the NHj moiety is important in determining the regiochemistry of the functionalization. 

Oxidation of Saturated Hydrocarbons, Ethers, and Alcohols. Surely the most striking reaction of dioxiranes is their ability to functionalize unactivated C-H bonds by the insertion of an oxygen atom into this rr-bond. This has opened up an important new area of oxidation chemistry. While DDO has been used in... 

Dioxiranes, generated by the oxidation of ketones with KHSOs, insert an oxygen atom into alkane C—H bonds with retention of configuration by an oxenoid mechanism related to that found for peracids. Tertiary C—H bonds are hydroxylated and react faster than secondary CH2 groups, which are completely oxidized to the ketone. Conversions of up to 50% have been observed." CF3(Me)C02 is a more recently developed reagent of the same type. These easily prepared reagents have considerable promise for organic synthesis. 

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