Pyridinium chlorochromate oxidation General

The scope of this asymmetric HDAR was evaluated under the optimized reaction conditions using o-benzoquinone diimide 268. Since the hemiaminal 270 was not stable enough for further analysis, PCC (pyridinium chlorochromate) oxidation was employed to produce the more stable quinoxalinones 271. As shown in Scheme 2.41, a variety of aldehydes 253 bearing simple linear or branched a-substituted alkyl groups were well tolerated and excellent enantioselectivities were generally obtained. 

General Procedure for Oxidation of Alcohols to Aldehydes and Ketones with Pyridinium Chlorochromate (PCC)237... 

Pyridinium chlorochromate (PCC) is a Cr(VI) salt formed between pyridine (CeHsN), HCI, and CrOs. PCC is soluble in dichloromethane, thus it can be used under conditions that exclude water, allowing for the oxidization of primary alcohols to aldehydes because the aldehyde hydrate is not present under anhydrous conditions. Jones reagent, on the other hand, oxidizes primary alcohols to carboxylic acids because it is an aqueous reagent. The following are some general examples of PCC oxidations. 

A specific oxidizing agent for the conversion of primaiy alcohols to aldehydes is pyridinium chlorochromate, abbreviated as py CrOsCl A Generally, the oxidation is run in methylene chloride solvent. For example. 

In Summary Reductions of aldehydes and ketones by hydride reagents constitute general syntheses of primary and secondary alcohols, respectively. The reverse reactions, oxidations of primary alcohols to aldehydes and secondary alcohols to ketones, are achieved with chromium(Vl) reagents. Use of pyridinium chlorochromate (PCC) prevents overoxidation of primary alcohols to carboxylic acids. 

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