New Cyclotrimerization of Aldehydes to Cyclopentenone or Tetrahydrofuran Induced by Dibromotriphenylphosphorane

Abstract

WOS:000274843100020International audiencealpha-Mono- or alpha-dialkylated aldehydes undergo cyclotrimerization in the presence of dibromotriphenylphosphorane (PPh(3)Br(2)) to afford cyclopentenones or tetrasubstituted tetrahydrofurans in good yields. These transformations proceed by a tandem aldol dimerization/Nazarov reaction or a tandem aldol dimerization/Prins cyclization

Catalytic Nazarov Cyclization: The State of the Art

“…[74] The 4p electron conrotation of the azirine in the iminium form (34) generates a cation that is trapped by water. Further protonation of the trapped adduct (35) promotes ring expansion to eventually afford a piperidone (38) in an enantiomeric ratio of 99:1. The reaction does not work in the absence of a b-aryl group that polarizes the enone.…”

The iso-Nazarov reaction

“…Scheme 21. A rearrangement involving an iso-Nazarov reaction.Heck and co-workers developed a domino double-aldol-condensation/iso-Nazarov cycloisomerization for the synthesis of cyclopentenones (Scheme 22) 43,44. Both propionaldehyde and butyraldehyde (106 with R Me and Et, respectively) were found to undergo self-trimerization when treated with equimolar amounts of dibromotriphenylphosphorane reagent (PPh3Br2) to afford the corresponding cyclopentenones 108a/b in moderate yields.…”

Recent Progress in the Synthetic Assembly of 2-Cyclopentenones

“…163 Finally, an unprecedented cyclotrimerization of α-monosubstituted aldehydes induced by dibromotriphenylphosphine has been described (Scheme 75). 164 The proposed mechanism consisted of a series of Lewis acid mediated aldol condensations going via a propenal to give a pentadienal, which isomerized before cyclizing via a Nazarovtype process to give the 2,3,5-trisubstituted 2-cyclopent-enone products 257. On this postulate, mixed condensations of aldehydes and enals were carried out using the same conditions to give the expected products 258.…”