Chiral Sulfinamide/Achiral Sulfonic Acid Cocatalyzed Enantioselective Protonation of Enol Silanes

Abstract

The application of chiral sulfinamides and achiral sulfonic acids as a co-catalyst system for enantioselective protonation reactions is described. Structurally simple, easily accessible sulfinamides were found to induce moderate-to-high ee's in the formation of 2-aryl-substituted cycloalkanones from the corresponding trimethylsilyl enol ethers.

Redox Non‐Innocence of Coordinated 2‐(Arylazo) Pyridines in Iridium Complexes: Characterization of Redox Series and an Insight into Voltage‐Induced Current Characteristics

“…A combination of a chiral sulfinamide and an achiral sulfonic acid was recently proposed by Jacobsen and co‐workers in the form of the efficient chiral acidic catalyst 26 , able to achieve EP of silyl enolates derived from cyclohexanones 3 and cycloheptanones 4 with high yields and enantioselectivities (Scheme ) 22. In association with 2,6‐di‐ tert ‐butylphenol as stoichiometric proton source (1.1 equiv.)…”

Asymmetric Organocatalytic Protonation of Silyl Enolates Catalyzed by Simple and Original Betaines Derived from Cinchona Alkaloids

“…[15] After quaternization of the quinuclidine moiety, the betaine was obtained by treatment with ion-exchanged resin (Amberlyst A26 OH form; Scheme 1). Several other chiral quaternary ammonium aryloxide salts were tested at this temperature (Table 1, entries [5][6][7][8][9][10][11][12][13][14]. First, we ensured that in the absence of catalyst no conversion could be detected (Table 1, entry 1).…”

Chiral Sulfinamides as Highly Enantioselective Organocatalysts

“…A thorough mechanistic study was conducted using triflic acid as the co‐catalyst showed that the selectivity stems from tight hydrogen bond interactions between sulfonate, sulfinamido urea and the iminium ion. These findings were exploited by Jacobsen and co‐workers to develop the enantioselective protonation of prochiral silyl enol ethers ( 51 ) using different tert ‐butanesulfinamide‐based catalysts together with different proton sources (Scheme ) 17. Although 42 a catalyzed the reaction (>95 % yield, 67 % ee ), the much simpler catalysts 50 a – d worked equally good or even better with 50 b being the best (>95 % yield, 75 % ee ), which shows that the urea moiety is not crucial for the catalysis.…”