Pyridinium Chlorochromate-Mediated Allylic and Benzylic Oxidation

Allylic and benzylic oxidation reactions with sodium chlorite

“…1 Relevant examples are the oxidation of D 5 -steroids to the corresponding biologically interesting D 5 -7-ketone derivatives 2 and the benzylic oxidation of xanthene to xanthone. 3 Traditionally, chromium(VI)-based reagents such as CrO 3pyridine complex, 4 CrO 3 and 3,5-dimethylpyrazole, 5 pyridinium chlorochromate (PCC), 6 pyridinium dichromate (PDC), 7 PDC-tert-butyl hydroperoxide, 8 sodium chromate, 9 sodium dichromate in acetic acid, 10 pyridinium fluorochromate, 11 3,5-dimethylpyrazolium fluorochromate (VI) 12 and a combination of an N-hydroxydicarboxylic acid imide with a chromium containing oxidant 13 have been used to perform these oxidations. However, the use of large excess quantities of both reagents and volume of solvent in most of these procedures, along with the difficult work-up of the environmentally hazardous chromium residues makes such procedures inconvenient on a commercial scale.…”

The allylic oxidation of unsaturated steroids by tert-butyl hydroperoxide using surface functionalised silica supported metal catalysts

“…The D 5 -steroids can be oxidised to 5-en-7-ones, which are known as inhibitors of sterol biosynthesis and have some use in cancer chemotherapy. 3 The allylic oxidation of unsaturated steroids such as D 5steroids, has traditionally been performed with chromium reagents such as CrO 3 -pyridine complex, 4 CrO 3 and 3,5-dimethylpyrazole, 5 pyridinium chlorochromate, (PCC), 6,7 pyridinium dichromate (PDC), 7 sodium chromate, 8 sodium dichromate in acetic acid, 9 pyridinium fluorochromate, 10 and 3,5-dimethylpirazolium fluorochromate(VI). 11 However, the great excess of ecologically and physiologically undesirable chromium reagent and the large volume of solvent required in these procedures, in combination with the difficult work-up and the production of environmentally hazardous chromium residues, causes such procedures to be inconvenient on a commercial scale.…”

Chemical Syntheses of 7‐Keto‐Δ5‐sterols

“…At room temperature, PCC in methylene chloride was an ineffective reagent for allylic oxidation (29). In contrast to these results, we have achieved moderate success by using PCC in refluxing methylene chloride for allylic and benzylic oxidations (41). PCC in DMSO also has been used for the oxidation of β-ionone to the corresponding diketone (42).…”

“…Under these conditions, refluxing acetone, pyridine, N,N-dimethylformamide, and DMSO at 100°C yielded 7-ketocholesteryl benzoate in 2, 0, 18, and 77% yield, respectively. In an earlier study, we found that using refluxing methylene chloride as solvent yielded 54% of 7-ketocholesteryl benzoate from cholesteryl benzoate (41).…”