Intramolecular Keto Lactam Condensation: A Convenient and Straightforward Approach to Bicyclic Vinylogous Lactams
Although the aldol condensation is a well-known reaction, the aza-type aldol condensation, namely, the intramolecular condensation of common keto lactams leading to bicyclic vinylogous lactams, is a highly demanding transformation, with potential applications in both organic synthesis and medicinal chemistry. The known methods for this type of cyclization require several steps. In this paper, we disclose a straightforward approach that consists of the in-situ formation of silyl enol ethers with tert-butyldimethylsilyl trifluoromethanesulfonate (TBDMSOTf), lactam activation with triflic anhydride (Tf2O), and a tandem cyclocondensation reaction. The reaction can be run in a one-pot manner or in a two-step fashion, both under mild conditions. The yields for the one-pot version were 52–80 %. In some cases, the two-step version gave higher overall yields (44–85 %) than the one-pot version.
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