A new stereocontrolled approach to fused polycyclic compounds containing a diketopiperazine ring

Representative (1S)- and (4S)-alkyl-1,4-dihydropyrazino[2,1-b]quinazoline-3,6-dione lactim ethers were regio- and diastereoselectively alkylated after metallation to give the corresponding 1,4-trans-isomers with retention of the stereocentres. The results were compared with the previously studied lactams. The (1R,4S)-dialkyl derivatives obtained by C(1)-alkyation with bifunctional reagents were lately cyclized to complex polycyclic compounds through a second N(2)-alkylation promoted by sodium iodide.