Synthesis of α-(aminoethyl)-α,ß-enones via alkyne aza-Prins cyclization and their synthetic application to pyrrolidines.

We developed a synthetic method for α-(aminoethyl)-α,ß-enones from aryl-substituted homopropargyl sulfonamides and aldehydes, representing the first synthesis of conjugated enones via alkyne aza-Prins cyclization. These products could be converted into pyrrolidines by a formal 5-endo-trig cyclization.

Alkyne aza-Prins cyclization of N-(hexa-3,5-diynyl)tosylamides with aldehydes using triflic acid and a binuclear aluminum complex.

The alkyne aza-Prins cyclization of 3,5-diynyl amides and various aldehydes was developed using TfOH with/without (Me2AlO)2SO2. This method, which could be applied to homopropargyl amides, provides TfO-substituted pyrrolidines with E-selectivities and exclusive regioselectivities. This work represents a first example of the aza-Prins cyclization with the introduction of TfO groups.