Unsaturated Amino Alcohols via Cyclization of Allylic Bistrichloroacetimidates

Abstract

In intramolecular allylic substitution of bistrichloroacetimidates, one of the imidate groups can serve as a N-nucleophile while the other can serve as a leaving group, leading to 2-vinyloxazolines. Two approaches based on different mechanisms for allylic substitution can be applied to achieve cyclization of the bisimidates. The reaction, catalyzed by palladium(II), presumably involves aminometalation of the double bond followed by deoxypalladation. Enantioenriched products can be obtained using chiral palladium(II) catalysts as demonstrated for the cyclization of achiral bisimidates derived from (E/Z)-butene-1,4-diol. Allylic substitution can proceed via a competing mechanism that involves carbenium ion formation from a metal-complexed imidate. This enables the use of Lewis acids as nonexpensive and less toxic alternative to palladium catalysts. Regioselectivity of Lewis acid catalyzed bisimidate cyclization is controlled by formation of the most stable carbenium ion as proposed intermediate. This approach provides an efficient access to vinylglycinols, butadienylglycinol, and C-quaternary vinylglycinols.