Nucleophilic additions to (4S)-1-alkylidene-2,4-dihydro-1H-pyrazino[2,1-b]quinazoline-3,6-diones

Investigation of the title compounds as didehydro amino acid templates showed their lack of reactivity against amines or Grignard reagents under copper(I) catalysis, but efficient additions to the exocyclic double bond took place with mercaptides or stabilized carbanions. Regio- and diastereoselective addition of organometallic reagents occurred at the C(3)-position and, in 1-methylene derivatives, these reactions were followed by a rearrangement of the intermediate oxy-anion to give pyrido[2,1-b]quinazolines.