Substituent Effects in the Aliphatic Claisen Rearrangements of Substituted (1-Methyl-3-oxahexa-1,5-dienyl)amines: Synthesis of Substituted 2-Aminopent-4-enals. Alternative -Sigmatropic Shifts in Related Aromatic Systems.

Article abstract of DOI:10.1021/jo00232a024

The series of substituted β-allyloxy enamines 4 was allowed to undergo Claisen rearrangement.The reaction proved to be faster for enamines derived from aliphatic than those from aromatic amines, the general substituent effects fitting Gajewski's oxaallyl-allyl radical model for these processes.The high stereoselectivity observed in these reactions leading to the 2-aminopent-4-enals 5 was assumed to occur via the more stable chairlike transition state.A different <1,3>-sigmatropic course, leading to the 2-amino-2-methylpropanals 20, was observed when the allylic double bond is part of an aromatic system.