Diastereoselective Conjugate Addition of α-Lithiodithioacetals to the α,β-Unsaturated Lactam Unit of 5,6-Dihydropyrrolo[2,1-a]isoquinolinones

Abstract

Diastereoselective conjugate addition of α-lithiodithioacetals to α,β-unsaturated bicyclic lactams is described. Typical yields of the resulting tetrahydropyrrolo[2,1-a]isoquinolinones ranged 60-90% with facial diasteeoselectivities of > 95 : 5, when there is a bulky butyl group at the α-position to the nitrogen atom. Cis or trans isomers could be obtained exclusively by using 1,3-dithianyllithium or bis(phenylthio)methyllithium as nucleophiles, respectively. The presence of a methyl group at the 10b position of the heterocyclic system diminished the stereoselectivity. In selected diastereomeric byciclic lactams the acyl group was unmasked.