Density functional theory study of the mechanism of the proline-catalyzed intermolecular aldol reaction

Density functional study of the l-proline-catalyzed α-aminoxylation of aldehydes reaction: The reaction mechanism and selectivity

“…Many reports [19] proposed that the enantioselectivity was induced by the addition of chiral enamine 5 to carbonyl compound and nitroso compound in the proline-catalyzed asymmetric reaction. Houk [19e] and Armando [19f] have reported different transition structures to explain the selectivity in proline-catalyzed asymmetric reaction.…”

Towards an Understanding of the Polar Diels–Alder Reactions of Nitrosoalkenes with Enamines: A Theoretical Study

“…Our interest in organocatalysis [19] prompted us to carry out a theoretical investigation of the DA reaction involved in the pyrrolidine-catalyzed reaction of nitrosoalkenes studied recently by Jorgensen and co-workers. [13] Two DA reactions have been studied.…”

A revisit to proline-catalyzed amination under basic conditions: Insight into the key intermediates and stereocontrolling transition state models for the reversal of enantioselectivity

“…In accordance with the experimental proposals [2,[4][5][6][7][8][9][10][11][12] and the theoretical studies of the enamine-mediated reactions [13][14][15][16][17][18][19][20][21][22][23][24][25], the representation to differentiate the nucleophilic intermediates and various stereochemical channels in the CAN bond forming step have been illustrated in Scheme 2. The different combinations of the s-cis or s-trans-conformations, the (E)-or (Z)-configurations of the enamine intermediates, and the anti-or syn-attacking modes of the electrophile to the enamine intermediates constitute the various stereochemical possibilities of the TSs in the CAN bond forming step.…”

“…Although various organocatalysts have been developed to reach high level of efficiencies and to widen the scope of substrates, proline, owing to its good performance in a broad range of asymmetric transformations such as aldol [4], Mannich [5], and amination reactions [6] etc., has been identified as a universal catalyst and is still the hot topic in the field of organocatalysis [1][2][3][4][5][6][7][8][9][10][11][12]. For the enamine-mediated process in proline catalysis, the widely accepted Houk-List transition state model (TSA in Scheme 1), which underlines that the proton of the enamine carboxylic acid (intermediate I in Scheme 2) plays an essential role in directing the electrophile approaching the above face of s-trans-enamine in the stereocontrolling addition step, has been successfully employed to rationalize the stereoselectivity of various reactions [2,[13][14][15][16][17][18][19][20][21][22][23][24][25]. Recently, several experimental evidences have shown that the reactivity and selectivity of the proline-catalyzed transformations are sensitive to the basic additives [7][8][9]11,12].…”