Synthesis of polycyclic heteroaromatic compounds via the intramolecular 4+2 cycloaddition of conjugated hetarenynes and alkynes

摘要

This dissertation describes studies of the feasibility and scope of intramolecular [4+2] cycloadditions of hetarenynes and alkynes as a method for the synthesis of polycyclic benzo[b]-fused five-membered heteroaromatic compounds. Only scattered reports of this transformation existed prior to our work and these were very limited in their scope. The research presented in this thesis demonstrates that the synthesis of benzo[b]-fused five-membered heteroaromatic compounds can be effectively carried out under relatively mild thermal conditions utilizing alkynylpyrroles, -thiophenes, or -furans tethered to alkynes. The hetarenyne cycloaddition substrates are readily prepared in 2-3 steps from commercially available or known 2- or 3-halohetarenes via Sonogashira coupling followed in most cases by a Mitsunobu reaction. In the majority of cases metalation of a terminal alkyne with a Grignard reagent and then reaction with various electrophilic reagents allows for the creation of a library of cycloaddition substrates. The scope of the hetarenyne cycloaddition was explored with respect to four major variables in the cycloaddition substrates: