Aza-annulation
of novel 1,2,3,4-tetrahydro-β-carboline derived
enaminones and nitroenamines with various 1,2- and 1,3-bis electrophiles,
such as oxalyl chloride, maleic anhydride, 1,4-benzoquinone, 3-bromopropionyl
chloride, itaconic anhydride, and imines (from formaldehyde and primary
amines), has been investigated. These methodologies provide simple
one-step pathways for efficient construction of highly functionalized
tetrahydro-β-carboline 1,2-fused, five- and six-membered heterocyclic
frameworks, such as indolizino[8,7-b]indoles, pyrido[1,2-a:3,4-b′]diindoles,
indolo[2,3-a]quinolizidines, and pyrimido[1′,6′:1,2]pyrido[3,4-b]indoles, which are core structures of many naturally occurring
indole alkaloids with diverse bioactivity.