Preparation of 3-aza-Cope rearrangement of N-alkyl-N-allyl enamines
摘要:
The [3,3] charge-accelerated rearrangement of N-allyl-N-isobutyl enamine substrates to gamma,delta-unsaturated imine products and subsequent reduction to the corresponding N-alkyl delta,epsilon-unsaturated amines is reported. Several routes to the N-allyl-N-isobutyl enamines were established for the enamine prepared from isobutyraldehyde. With use of the most efficient route developed, enamines derived from butanal, 2-phenylpropanal, cyclohexanone, and cyclopentanone were prepared in 58 to 92% overall yield in three steps from allylamine. In the case of butanal, the E isomer was formed exclusively, while the enamine from 2-phenylpropanal was prepared with an E to Z selectivity of 86:14. Heating these N-allyl-N-isobutyl enamines in refluxing dioxane with 0.5 equiv of HCl produced [3,3] rearrangement for substrates derived from isobutyraldehyde, 2-phenylpropanal, and cyclohexanone; the enamines of n-butanal and cyclopentanone were found to react through alternate pathways.