Sequential Double α-Arylation of N-Allylureas by Asymmetric Deprotonation and N→C Aryl Migration
摘要:
On lithiation with lithium amides, N-allyl-N'-aryl ureas undergo rearrangement with transfer of the aryl ring from N to the allylic alpha carbon. From the alpha-arylated products, a further aryl transfer under the influence of a chiral lithium amide allows the enantioselective construction of 1,1-diarylallylamine derivatives. Stereoselectivity in these reactions results from the enantioselective formation of a planar chiral allyllithium under kinetic control.
Geometry-Selective Synthesis of E or ZN-Vinyl Ureas (N-Carbamoyl Enamines)
摘要:
N-Vinyl ureas are emerging as a valuable class of compounds with both nucleophilic and electrophilic reactivity. They may be made by capturing the enamine tautomer of an imine with an isocyanate, a reaction which in general leads to the E isomer of the vinyl urea. Deprotonation of such a vinyl urea, or of an allyl urea, generates a dipole stabilized Z-allyl anion which may be protonated to return the Z-vinyl urea. Isomerization of an allyl urea with a Ru complex provides an alternative route to E-vinyl ureas.