Triflic Acid-Catalyzed Enynes Cyclization: A New Strategy beyond Electrophilic π-Activation

The cyclization of enynes, catalyzed by a transition metal, represents a powerful tool to construct an array of cyclic compounds through electrophilic π-activation. In this paper, we disclose a new and efficient strategy for enynes cyclization catalyzed by triflic acid. The salient features of this transformation includes a broad substrate scope, metal free synthesis, open flask and mild conditions, good yields, ease of operation, low catalyst loading, and easy scale-up to gram scale. A preliminary mechanism study demonstrated that the activation model of the reaction was σ-activation, which is different from the transition-metal-catalyzed enynes cyclization. Our strategy affords a complementary method to the traditional strategies, which use transition-metal catalysts.

Synthesis of 4H-chromenes by an unexpected, K3PO4-mediated intramolecular Rauhut–Currier type reaction

The K₃PO₄-mediated intramolecular Rauhut-Currier type reaction of chalcones having an enoate moiety leading to the formation of 4H-chromenes in moderate to good yields is demonstrated.

Aza-Morita–Baylis–Hillman reactions catalyzed by a cyclopropenylidene

Catalysis using a bis(dialkylamino)cyclopropenylidene (BAC) has been developed, which relies on a formal umpolung activation of Michael acceptor pro-nucleophiles.

Morita-Baylis-Hillman Reaction of β,β-Disubstituted Enones: An Enantioselective Organocatalytic Approach for the Synthesis of Cyclopenta[b]annulated Arenes and Heteroarenes

The first enantioselective organocatalytic intramolecular Morita-Baylis-Hillman (MBH) reaction of sterically highly demanding β,β-disubstituted enones is presented. The MBH reaction of β,β-disubstituted-α,β-unsaturated electron-withdrawing systems was previously considered to be unfeasible. Towards this end, designer substrates, which under simple and practical reaction conditions generate a variety of cyclopenta[b]annulated arenes and heteroarenes in excellent enantiopurities and near-quantitative yields in remarkably short reaction times, are described. The reason for the unusually facile nature of this reaction is attributed to the synergy guided and entropically favored intramolecular reaction. Further, this strategy provides easy access to a substantial number of bioactive natural products and pharmaceutically significant compounds.