Reversal of Diastereoselection in the Conjugate Addition of Cuprates to Unsaturated Lactams

We
report that the stereochemical outcome of the conjugate addition
of organocopper reagents to bicyclic α,β-unsaturated lactams
derived from pyroglutaminol is determined by the nature of the aminal
group. Bicyclic α,β-unsaturated lactams in which the aminal
is derived from a ketone have been found to afford products of syn conjugate addition. By contrast, bicyclic α,β-unsaturated
lactams in which the aminal is derived from an aldehyde afford products
of anti conjugate addition. These remarkably different
results obtained from very similar starting materials are unexpected.