Multivalency as a key factor for high activity of selective supported organocatalysts for the Baylis-Hillman reaction.
The polystyrene-supported N-alkylimidazole-based dendritic catalysts for the Baylis-Hillman reaction exhibit one of the strongest beneficial effects of multivalent architecture ever reported for an organocatalyst. The yields in the model reaction of methyl vinyl ketone with p-nitrobenzaldehyde are more than tripled when a non-dendritic catalyst is replaced by a second- or third-generation analogue. Moreover, the reaction of the less active substrates will not occur with the non-dendritic catalyst and will proceed to a significant extent only with the analogous catalysts of higher generations. A substantial additional enhancement of the reaction yield could be achieved by increasing the content of water in the reaction solvent. The plausible cause of the dendritic effect is the assistance of the second, nearby imidazole moiety in the presumably rate-determining proton transfer in the intermediate adduct, after the first imidazole unit induced the formation of the new carbon-carbon bond.
School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel-Aviv University, Tel-Aviv 69978 (Israel); Current Address: Teva Pharmaceutical Industries Ltd, P.O.B. 3190, 2 Denmark Street, Petah Tikva (Israel).
Kerem
K
Goren
Jeny
J
Karabline-Kuks
Yael
Y
Shiloni
Einav
E
Barak-Kulbak
Scott J
SJ
Miller
Moshe
M
Portnoy
D002384:Catalysis; D050091:Dendrimers / Q000737:chemistry; D007659:Ketones / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D011137:Polystyrenes / Q000737:chemistry*
D050091:Dendrimers; D007659:Ketones; D011137:Polystyrenes
NMR spectroscopy; dendrimers; organocatalysis; polymers; supported catalysts