Organocatalytic asymmetric α-benzoyloxylation of α-branched aldehydes and enals: a useful approach to oxygenated quaternary stereocenters

Organocatalytic γ-oxidation of α,β-unsaturated aldehydes

“…20,21 For this purpose various electrophilic oxidizing agents were employed including benzoyl peroxide (BPO), [22][23][24][25] Inspired by these reports we envisaged that electrophilic BPO could, in a similar manner, react with dienamines. Since various organocatalysts have been used to generate dienamine from α,β-unsaturated aldehydes we tested a broad range of amino acids 1-6 and their derivatives 7-9 as organocatalysts in the reaction of (E)-2-hexenal (10) with dibenzoyl peroxide (Figure 1 Figure 1.…”

“…Unfortunately, the reaction in the presence of simple secondary amine -pyrrolidyne While we were working on γ-oxygenation of carbonyl compounds, List and co-workers reported that treatment of α-branched α,β-unsaturated aldehydes with BPO in the presence of quinine-derived amine and trichloroacetic acid as a co-catalyst led predominantly to benzoyloxylation at the α-position. 25 The α/γ ratio was high for acyclic substrates but in some cases it diminished by a silica gel mediated allylic rearrangement of α-benzoyloxy products to their γ-counterparts.…”

Asymmetric organocatalysis mediated by primary amines derived from cinchona alkaloids: recent advances

“…Continuing their investigations, List et al applied cinchona-based primary amines in the α-benzoyloxylation of α-branched aldehydes and enals (Scheme 12). 28 In the presence of the primary amine IIa and (S)-3,3′-bis(2,4,6triisopropylphenyl)-1,1′-bi-2-naphthol cyclic mono-phosphate ((S)-TRIP), benzoyl-protected hydroxyaldehydes 35 containing an α-quaternary stereocenter were obtained in moderate to good yields and ee values. In the process, the radical inhibitor 2,6-di-tert-butyl-4-methylphenol (BHT) was used to prevent possible benzoyl radical side reactions.…”

7.07 α-Oxygenation of Carbonyl Compounds

“…45 The method could also be extended to the use of a-branched aldehydes, but lower selectivities were observed. 46 …”