Development of a New Lewis Acid Catalyzed [3,3]‐Sigmatropic Rearrangement: The Allenoate‐Claisen Rearrangement.

Abstract

A new Lewis acid-catalyzed Claisen rearrangement has been developed that allows the stereoselective construction of β-amino-α,β,e,ζ-unsaturated-γ,δ-disubstituted esters from simple allylic amines and allenoate esters. This reaction, which is contingent upon the use of Lewis acid, can be conducted with a range of metal salts (Yb(OTf)3, AlCl3, Sn(OTf)2, Cu(OTf)2, MgBr2·Et2O, FeCl3, Zn(OTf)2) with catalyst loadings as low as 5 mol %. This catalytic process provides access to a diverse range of β-amino-α,β,e,ζ-unsaturated-γ,δ-disubstituted esters in high yield and with excellent levels of diastereoselectivity for a series of allyl pyrrolidines (R1 = H, Me, i-Pr, Ph, NR2 = pyrrolidine, piperidine, NMe2; ≥81% yield, ≥94:6 syn:anti) and allenoate esters (R2 = H, Me, i-Pr, Ph, allyl, NPht, Cl; ≥75% yield, ≥91:9 syn:anti). The capacity of this new Claisen rearrangement to provide catalytic access to elusive structural motifs has also been demonstrated in the stereospecific formation of quaternary carbon bearing fr...