Enantioselective Organocatalysis Using SOMO Activation
The asymmetric α-addition of relatively nonpolar hydrocarbon substrates, such as allyl and aryl groups, to aldehydes and ketones remains a largely unsolved problem in organic synthesis, despite the wide potential utility of direct routes to such products. We reasoned that well-established chiral amine catalysis, which activates aldehydes toward electrophile addition by enamine formation, could be expanded to this important reaction class by applying a single-electron oxidant to create a transient radical species from the enamine. We demonstrated the concept of singly occupied molecular orbital (SOMO) activation with a highly selective α-allylation of aldehydes, and we here present preliminary results for enantioselective heteroarylations and cyclization/halogenation cascades.
Additional Information© 2007 American Association for the Advancement of Science. 20 February 2007; Accepted 20 March 2007; Published online 29 March 2007. We thank R. A. Pascal for invaluable assistance in performing Gaussian DFT calculations and M. Amatore for a late-stage experimental contribution. Financial support was provided by NIH National Institute of General Medical Sciences (grant R01 GM078201-01-01) and by gifts from Amgen, Merck Research Laboratories, and the Astellas Foundation USA. T.D.B. is grateful for a Novartis predoctoral fellowship, J.-B.H. is grateful for a KRF postdoctoral fellowship, and K.A. is grateful for a Merck overseas postdoctoral fellowship.
Supplemental Material - Beeson-SOM.pdf