Pivaldehyde, oxidation

The reaction occurs with some enantioselectivity and requires the presence of pivaldehyde (which is also oxidized)29,30. The reaction occurs for many other alkenes using transition metals coordinated to 1,3-diketone type ligands31-34. Use of a cobalt(II) complex and aldoacetal in place of the Mn(III) compound and pivaldehyde gives a novel method for the synthesis of acid-sensitive epoxides35. 

These reactions lead to optically active products when an optically active phosphine is used in place of triphenylphosphine. Thus treatment of the enol of optically active 6 with pivaldehyde gives the aldol 7 in 98% isolated yield. The absolute configuration was confirmed by X-ray diffraction. Only one method is known at the present time for removal of the metal moiety. Thus oxidation of 7 with ferric chloride affords the optically pure cyclobutanone 8 in 70% yield. 

Alkynyl(phenyl)iodonium triflates react with pivaldehyde oxime in the presence of iodosylbenzene to give the isoxazoles 278 (Scheme 79) (97TL8793). Although the purpose of iodosylbenzene was to oxidize the oxime to the corresponding nitrile oxide, thus providing access to isoxazolyliodonium salts, its overall influence on the outcome of these reactions has not been firmly established. 

Phthalic acid, 259 Phthalic anhydride, 104 a-Picoline, 161 a-Picoline N-oxide, 161 Picolinic acid, 16 Picramic acid, 271 Picric acid, 271 Pinacol reduction, 7 Pinosylvin, 31 Piperazines, 322 Piperidine, 33, 291 2-Piperidone, 194 Pivaldehyde, 105 Podophyllotoxin, 337 Podophyllotoxone, 337 Polonovski reaction, 308 Polyisoprenoids, 300-301 Polymethoxybenzophenones, 30—31 Polymethylhydrosiloxane, 294 Polyphosphate ester (PPE), 229-230 Polyphosphoric acid, 227, 231—232 Potassium, 232, 233 Potassium acetate, 96 Potassium amide, 232—233, 310 Potassium azodicarboxylate, 100 Potassium r-butoxide, 26, 45, 47, 77-78, 85, 133, 188, 212, 222, 225, 233-234, 236, 246... 

Mukaiyama and coworkers [1378] have performed such oxidations with molecular oxygen in the presence of pivaldehyde under catalysis with related salen 3.70 Mn(lH) complexes however, lower enantioselectivities were obtained. The use of various manganese or iron porphyrins as catalysts also gives lower enantioselectivities [971, 1379, 1379a], as do the oxidations with chiral oxaziridines in stoichiometric amounts [741],... 

Interestingly, Suzuki and coworkers demonstrated that Ir(III) catalysts could promote formal ketone hydroacylation of 1,5-ketoaldehydes, yielding either isocou-marins or 3,4-dihydroisocoumarins (Scheme 2.43). The presence of pivaldehyde as an oxidant favors the formation of isocoumarins. The mechanism of this transformation involves a transfer hydrogenation process (see Section 2.5.1) [88]. 

Fig. 5.2 Cobalt-catalyzed alcohol oxidation with pivaldehyde additive.

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