PCC: Novel oxidation reactions

Abstract

(A) The oxidant and slightly acidic character of PCC is able to convert allylic tertiary alcohols or tertiary vinyl alcohols into α,β-unsaturated carbonyl compounds. (B) PCC shows an unusual behavior as dienophile and oxidant in the ring enlargement of 2-furyl carbinols to pyran derivatives. (C) The deoxamination of oximes to regenerate the carbonyl compound is also mediated using PCC. However, PCC/H2O2 system is more effective as a deblocking agent. (D) Hydroboration of 1-alkenes give trialkyl boranes which on subsequent oxidation with PCC furnish aldehydes. PCC oxidation of borate esters or boroxines also give aldehydes. (E) PCC oxidation of tertiary 2-alkyl cyclopropyl carbinols furnished transposed β,γ-enones, making the overall process a synthetically useful method for 1,4-carbonyl transposition. (F) PCC can release quinone from hydroquinone silyl ethers. (G) The allylic alcohols obtained from lithiated 1,4-dioxene and ketones or aldehydes undergo regiospecific oxidative cleavage with PCC at the dioxene double bond to furnish, after saponification, α-hydroxy acids. Extension of this reaction to α,β-unsaturated ketones affords α-keto acids. (H) Specific oxidative cleavage of allylic and benzylic ethers is known with PCC. (I) Oxidation of homoallylic alcohol with excess of PCC gave products arising from alcohol oxidation, double bond migration with isomerization from the cis- to the trans-olefin and subsequent allylic oxidation. Thus, this constitutes a synthetically useful conversion of homoallylic alcohols to 1,4-dicarbonyl-2-ene compounds.