Using an optimised carbohydrate-based bis(oxazoline) ligand and
copper(I) triflate, unactivated aliphatic alkenes were cyclopropanated with
simple ethyl diazoacetate, giving the corresponding products in
good yields and high stereoselectivities. The trans-disubstituted
cyclopropyl carboxylic acid ester derived from 1-nonene was subsequently
used as the key intermediate for the synthesis of the (+)-enantiomer
of the natural product (-)-grenadamide. The efficient and
high-yielding approach towards grenadamide reported here is the
first to utilise asymmetric cyclopropanation for the construction
of the chiral cyclopropyl unit.
carbohydrates - ligand design - asymmetric
catalysis - natural products - cyclopropanation
