Allylic C-H oxidation

Allylic C—H oxidation is known to occur if 1,4-dienes are treated with PDC in boiling chloroform (equation 16). hi the presence of r-butyl hydroperoxide, PDC becomes an effective allylic and... 

Fig. 30 Highly chemoselective methods for intra- and intermolecular allylic C-H oxidation...

Kharasch-Sosnovsky Type of Allylic C-H Oxidation its Mechanism and Stereocontrol... 

The Collins oxidation is efficient for the preparation of carbtxiyl compounds in the presence of a wide range of functionalities (Table 2) however, Dauben and coworkors observed that extended expMure to the complex (24 h at room temperature) can give moderate to excellent yields of allylic C—H oxidation products (equations 3 to 5). ... 

Similarly, allylic C-H oxidation can streamline the eonstruetion of oxygenated compounds by reducing functional group manipulations necessary for working with bisoxygenated intermediates. For example, a chiral allylic C-H oxidation/enzymatic resolution sequence furnished bisoxygenated compound 14 in 97% ee and in 42% overall yield in just 3 steps from a commercially available... 

Lewis acid, In(0CF3S02)3, catalysed allylic C—H oxidation of aryl cycloalkenes by l-(propyl thio)pyrrolidine-2,5-dione in the presence of CH2CI2 and various nucleophiles (ROH, RCO2H, RSO2NH2) resulted in the formation of allylic ethers, esters, and sulfonamides in 52-83% yields electron-rich substrates were the most reactive. Other aryl cycloalkenes such as 1-naphthyl, l-(3-thiophenyl)-cyclohexene, 1-phenylcycloheptene, and 1-phenylcyclopentene were suitable substrates. Mechanistic studies showed that the sulfenamide played an important role in converting the allyl sulfide intermediate into the products. ... 

When the use of nucleophiles other than water in the presence of terminal alkenes under Pd(II) catalysis Wacker-type products frequently predominate. Use of White s electrophilic ftts-sulfinyl Pd(ll) acetate catalyst with terminal alkenes in the presence of acetic acid enabled the preparation of terminal acetoxylated olefins via allylic C—H oxidation and subsequent regioselective nucleophilic trapping of a Pd 7i-allyl complex (Table 3.3). The substrates screened afforded the desired end products with high levels of fi-selectivity and in moderate yields with excellent linear branched ratios. Recent updates to this method include the use of A-tosylcarbamates as nucleophiles. ... 

Oxidative Heck reactions via Pd(II) C—H functionalization of terminal alkenes with pinacol boranes have been described for the preparation of styrenes and derivatives through electrophilic Pd(II) catalysis (Scheme 3.20). ° Treatment of a functionalized allylic precursor with the Pd(II) catalysts listed facilitated an allylic C—H activation. Subsequent transmetallation of the aryl boronic acid and reductive elimination afforded the desired olefin with excellent stereoselectivity. The scope of the transformation allows for a variety of activating and deactivating substituents on the aryl boronic acid as well as numerous functional groups on the starting alkene. A tandem allylic C—H oxidation/vinylic arylation protocol has also been reported. " ... 

White et aJ. [711 reported macrolactonization reaction that proceeds via allylic C - H oxidation of linear to-alkenoic acids to furnish 14- to 19-membered alkyl and aryl macrolides, promoted by 10mol% Pd(OAc)2/phenyl bissulfoxide/benzoquinone system (Scheme 6.8). 

Scheme 3.41 Synthesis of chromans, isochromans, and pyrans via allylic C-H oxidation.

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