Synthesis and Evaluation of Enantiopure HMPA Analogs in Samarium‐Diiodide‐Promoted Dearomatizations of N‐Acylated Indole Derivatives

A series of (S)-proline-based enantiopure phosphorus triamide derivatives were prepared and evaluated as HMPA alternative in samarium diiodide cyclization reactions N-acylated indole derivatives. The expected tricyclic indoline generally obtained good to excellent yields, however, the induced enantioselectivities at best moderate. In our model reaction, derivative with a (dimethyl)hydroxymethyl group stereogenic center provided product almost quantitative yield an enantiomeric excess approximately 24 %. No separate proton source is required by applying this chiral Lewis base which was recovered 93 % yield. Bulkier substituents did not furnish improved results. Although preliminary study only low moderate could be achieved, observed fast conversions high yields demonstrate basic suitability pyrrolidine-based phosphoramide bases samarium(II)-induced reactions.