Reactions of Cyclopropyl Aryl Ketones with Sulfonamides Mediated by Zr(OTf)₄: Cascade Preparation of 5-Aryl-3,4-dihydro-2H-pyrrole

Abstract

We found that the Lewis acid Zr(OTf)₄ can effectively promote the ring-opening reaction of cyclopropyl aryl ketones with sulfonamides. By controlling the reaction conditions, we could obtain the ring-opened products 3 and the cyclized products 5 in moderate to good yields. This process provides a novel and efficient route for the synthesis of 5-aryl-3,4-dihydro-2H-pyrrole in the presence of a Lewis acid.

Key words

cyclopropyl aryl ketones - Lewis acid - Zr(OTf)₄ - ring-opening reaction - sulfonamides - cyclization - 5-aryl-3,4-dihydro-2H-pyrrole

References

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3

In the presence of catalytic amount of Zr(OTf)₄, a prolonged reaction time was required. During a prolonged reaction time, this reaction accompanied the cyclized product 5. In order to accelerate the reaction rate and let the reaction complete within a short time to give the ring-opened compound 3 as a major product, Zr(OTf)₄ (100 mol%) was employed.

4

A variety of Lewis acids and solvent have been tested in this reaction (unpublished results from our laboratory). As a result of these investigations, we found that Zr(OTf)₄ is the best Lewis acid for this reaction.