Development of Enantioselective Halogen-Catalyzed Reactions
Final Report Abstract
Initially, our approach started with the latter one employing styrene as the substrate and using the well known iodine(III) compound prepared first by Ishihara and coworkers. Through screening of different reaction conditions, including the terminal oxidant, additive and solvent(-mixture), we have been able to identify the best suitable reaction conditions, affording the diacetoxylated styrene in both good yield and enantioselectivity. A subsequent screening of different in situ generated hypervalent iodine(III) compounds demonstrated that our new hypervalent iodine(III) reagents, bearing an adamantyl moiety, proved to be very efficient catalysts. Under the optimal reaction conditions more than 20 different styrenes, including para-, meta-, ortho- and higher substitution pattern, could be converted into the corresponding diacetoxylated products with good yields and good enantioselectivities. The scope of the reaction could also be extended to the substrate class of internal alkenes. Cinnamyl alcohol and its derivatives underwent diacetoxylation in good to very good diastereoselectivities as well as enantioselectivities. Based on our optimization studies and several control experiments a mechanistic proposal explains the outcome of the intermolecular catalysis. Both, the Prèvost- on the one hand and the Woodward-mechanism on the other hand are conceivable pathways. Furthermore, we conducted initial experiments to realize the corresponding intermolecular diamination reaction, without any success yet. Several attempts to identify suitable reaction conditions under hypervalent iodine(III) catalysis failed. As oxidative diamination reactions are one of the main research interests, the Muñiz group will undertake further efforts to accomplish the intermolecular diamination of alkenes under chiral hypervalent iodine(III) catalysis.
Publications
- Review – Vicinal Difunctionalization of Alkenes with I(III) Reagents and Catalysts. Chem. Asian J. 2014, 9, 972–983
R. M. Romero, T. H. Wöste, K. Muñiz
(See online at https://doi.org/10.1002/asia.201301637)
