Here we report the use of the hexadehydro-Diels-Alder (HDDA) reaction for the de novo construction of a benzenoid ring in fused polycyclic heteroaromatic carbazole (i.e., [2,3]-benzoindole) skeletons. The strategy allows creation of highly substituted benzenoids. We also describe the HDDA-enabled chemical synthesis of the natural product alkaloids mahanimbine and koenidine. Trapping of the intermediate carbazolyne with a conjugated enal, proceeding through formal [2+2] cycloaddition, 4π-electrocyclic ring opening, and 6π-electrocyclic ring-closing events, constitutes a robust method for producing pyranocarbazoles.
Bibliographical noteFunding Information:
This research was supported by the National Institutes of Health (GM65597). NMR spectral data were collected with instrumentation acquired through the NIH Shared Instrumentation Grant program (S10OD011952). T.W. received support from a Wayland E. Noland Fellowship and a University of Minnesota Graduate School Doctoral Dissertation Fellowship.
© 2016 American Chemical Society.