PALLADIUM-CATALYSED CYCLISATION OF ENANTIOPURE ALLENIC LACTAMS PREPARED FROM A PYROGLUTAMIC ACID DERIVED ORGANOZINC REAGENT

A route for the synthesis of enantiopure allene-substituted lactams has been developed. The key-step involves the copper(I) mediated SN2’ substitution of propargylic tosylates by a (S)pyroglutamic acid derived organozinc reagent. Pd-catalysed reaction of these allenes with iodobenzene afforded enantiopure bicyclic enamides. Furthermore the unexpected formation of an interesting diene is reported. Palladium-catalysed reaction of heteroatom nucleophiles with allenes provides access to a manifold of interesting compounds.1-3 In most examples the nucleophile attacks one of the sp2-carbon atoms of the allene.4 Recently, we showed that in the palladium-catalysed reaction between iodobenzene and allenic lactams 1 an unprecedented process occurs in which the allenic tether is attacked by nitrogen at the central sp-carbon atom, leading to cyclic enamides 2 (eq 1).5,6