Enantio‐ and Diastereoselective Michael Reaction of 1,3‐Dicarbonyl Compounds to Nitroolefins Catalyzed by a Bifunctional Thiourea.

Abstract

Enantioselective syntheses O 0031Enantio-and Diastereoselective Michael Reaction of 1,3-Dicarbonyl Compounds to Nitroolefins Catalyzed by a Bifunctional Thiourea. -The title reagent OATU is found to be a highly efficient catalyst for asymmetric Michael reaction of various 1,3-dicarbonyl compounds with nitroolefins. It allows the generation of a quaternary carbon center with excellent diastereo-and enantioselectivity (to be continued). -(OKINO, T.; HOASHI, Y.; FURUKAWA, T.; XU, X.; TAKEMOTO*, Y.; J. Am.

C2‐symmetric sulfonamides as homogeneous and heterogeneous organocatalysts that mimic enzymes in enantioselective Michael additions

“…Enantiomeric excesses were determined by HPLC, and the absolute configuration was assigned by comparing t R with literature values …”

“…Heterogeneous catalysis: After 120 hours, the immobilized organocatalyst is separated by filtration; the filtrate was evaporated under reduced pressure to afford the products. The enantiomeric excesses were determined by HPLC, and the absolute configuration was assigned by comparing the retention time ( t R ) with literature values . For the products of addition of acetone to β‐nitrostyrene, t R for enantiomers S and R are: t R (minor) = 29.5, t R (mayor) = 42.7 minutes, respectively; for cyclohexanone to β‐nitrostyrene, t R for enantiomers SS , RR , RS , and S R are: t R (minor) = 12.1, t R (mayor) = 18.0, t R (minor) = 17.9, t R (mayor) = 18.1 minutes, respectively; for isobutyraldehyde to β‐nitrostyrene, t R for enantiomers S and R are: t R (minor) = 11.9, t R (mayor) = 13.9 minutes, respectively.…”

Synthesis of 2‐(3‐(3,5‐bis(trifluoromethyl)phenyl)thioureido)‐3‐((dimethylamino)methyl)camphor organocatalysts

“…Compounds 7 , 8 , 9 , 19 / 19 ’ have been evaluated as organocatalysts in a model reaction of Michael addition of dimethyl malonate to trans ‐β‐nitrostyrene (Table ). An equivalent of trans ‐β‐nitrostyrene ( 21 ), 2 equivalents of dimethyl malonate ( 20 ), and 10% of catalyst in toluene were used . Borneol derivatives 19 / 19 ’ gave no traces of the corresponding product 22 because of the lack of the basic functionality in the catalyst (Entry 1).…”

“…Characterization of Michael addition product ( 22 ): HPLC analysis: CHIRALPAK AD‐H, n ‐Hexane/ i ‐PrOH = 80:20, flow rate: 1.0 ml/min, 25 °C, UV: λ = 210 nm, t (minor) = 11 min, t (major) = 13 min. Absolute configuration was determined by comparing the relative retention time of the HPLC analysis with the reported data …”

“…Bifunctional (thio)urea derivatives comprise the bulk of noncovalent organocatalysts, which can achieve electrophile and nucleophile binding and activation through hydrogen‐bonding interactions. The preferred substituent is the electron‐poor 3,5‐bis(trifluoromethyl)phenyl‐group attached through thiourea functionality to a suitable chiral scaffold . Concerning the camphor‐derived noncovalent organocatalysts, the vast majority represent the pyrrolidinyl–camphor‐derived bifunctional organocatalysts, where both camphor and pyrrolidine chiral frameworks, connected with an appropriate linker, act in synergy (Fig.…”