Event Information
Stereochemistry and Mechanism of the Brønsted Acid-Catalyzed Intramolecular Hydrofunctionalization of Unactivated Alkenes
- Abstract:
The addition of O-H or N-H bonds across the C=C bond (hydrofunctionalization) of alkenes that are not electronically activated is especially useful in the target synthesis of heterocyclic natural products and in industrial synthetic processes. It has recently been shown that many hydrofunctionalization reactions purported to be catalyzed by metal triflates may be catalyzed by triflic acid generated in situ. The assumption that a Brønsted acid-catalyzed addition across an alkene will exhibit poor to no stereoselectivity due to the formation of a carbocation intermediate is commonly used as a basis for supporting transition metal catalysis. Herein is reported that intramolecular, trflic acid catalyzed hydrofunctionalization of deuterium labeled -alkenyl sulfonamides and alcohols and -alkenyl carboxylic acids efficiently and exclusively (≥95%) forms anti-addition products. Likewise, N-deuterated sulfonamide cyclizes solely via anti-addition and shows no evidence of deuterium scrambling due to carbocation formation. An AdE3–type mechanism is proposed and supported by stereochemical and kinetic analyses.
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