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
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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4 A variety of Lewis acids and solvent have been tested in this reaction (unpublished results from our laboratory).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.
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