Advancing the Morita–Baylis–Hillman Chemistry of 1‐Formyl‐β‐carbolines for the Synthesis of Indolizino‐indole Derivatives

The chemistry of the Morita–Baylis–Hillman adducts of 1‐formyl‐β‐carbolines has been extended for obtaining indolizino‐indole derivatives which mimic the harmicine and homofascaplysin frameworks. Adducts of N ‐substituted methyl 1‐formyl‐9 H ‐β‐carboline‐3‐carboxylate yield indolizino‐indole derivatives upon bromination followed by aqueous workup. On the other hand, N ‐substituted 1‐formyl‐9 H ‐β‐carbolines give rise to similar products in a one‐pot DABCO‐promoted reaction of activated alkenes. Alternatively, the DMAP‐mediated Morita–Baylis–Hillman reaction of N ‐substituted methyl 1‐formyl‐9 H ‐β‐carboline‐3‐carboxylate with cycloalkenones yields adducts that cyclize intramolecularly in the presence of PBr 3 to yield compounds with the homofascaplysin framework. In contrast, the DMAP‐mediated reaction of N ‐substituted 1‐formyl‐β‐carboline with cyclohexenone directly gives a product with similar framework in a single step.