A direct α-functionalization of simple aldehydes under N-Heterocyclic Carbene (NHC) catalysis and direct generation of ester enolate equivalents from nonfunctionalized aldehydes are disclosed. The catalysis involves selective enolate generation from an oxidatively generated NHC-bounded ester intermediate as a key step. The ester enolate intermediates undergo stereoselective reactions with enones and trifluoromethyl ketones.
The first chiral phosphine-catalyzed activation of acrylates for intramolecular formal [2 + 4] reactions with unsaturated imines is described. The catalytic reactions afford N-heterocycles with exceptionally high diastereo- and enantioselectivities. The [2 + 4] products are amenable for further transformations to useful molecules such as chiral piperidines and multicyclic structures.
Enantioselective Intramolecular Formal [2 + 4] Annulation of Acrylates and α,β-Unsaturated Imines Catalyzed by Amino Acid Derived Phosphines. -The title reaction allows a new, efficient, and highly stereoselective access to various chromenopyridinone derivatives. The latter can smoothly be converted into related compounds such as (IV), (V), and (VII). -(JIN, Z.; YANG, R.; DU, Y.; TIWARI, B.; GANGULY, R.; CHI*, Y. R.; Org. Lett. 14 (2012) 12, 3226-3229, http://dx.
Direct α-Functionalization of Simple Aldehydes via Oxidative N-Heterocyclic Carbene Catalysis. -The protocol applies a stoichiometric amount of quinone as an oxidant and proceeds via oxidative enolate formation to afford γ-lactones with high yields and complete enantioselectivity. Alternatively the products can be obtained using cheaper oxidant MnO2 and a catalytic amount of quinone [cf. (IIIa,b)]. Trifluoromethyl aryl ketones react under the reaction conditions to afford β-lactones (IX) in moderate yields and diastereoselectivity. -(MO, J.; YANG, R.; CHEN, X.; TIWARI, B.; CHI*, Y. R.; Org. Lett. 15 (2013) 1, 50-53, http://dx.
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