One-pot asymmetric synthesis of a hexahydrophenanthridine scaffold containing five stereocenters via an organocatalytic quadruple-cascade reaction

An organocatalytic enantioselective aza-Michael-Michael-Michael/aldol cyclization quadruple-cascade reaction of 2-amino-β-nitrostyrenes and α,β-unsaturated aldehydes has been developed for the construction of fully substituted hexahydrophenanthridine.

Achieving Molecular Complexity via Stereoselective Multiple Domino Reactions Promoted by a Secondary Amine Organocatalyst

In the last two decades, organocatalysis has emerged as an intensively investigated and rapidly growing area of research facilitating many known and many new transformations to provide efficient novel entries to complex molecules of high stereochemical purity. The organocatalysts have not only shown their efficiency for catalyzing the reactions in which one bond is formed, but they have also been effectively exploited in various versions of one-pot reactions. Domino reactions are one of the most important classes of one-pot reactions, where the target structure can be obtained in one pot without changing any reaction conditions while each reaction occurs as a consequence of the intermediates generated in previous steps. Owing to the synthetic importance and operational advantages associated with the use of organocatalysts and the development of domino reactions, various asymmetric transformations leading to a complex structure of choice have been explored. The early era of organocatalysis exhibits a limited growth in the development of asymmetric domino reactions with special emphasis on two reactions occurring one after the other. In 2006, our group made a step forward to develop more complex domino reactions catalyzed by a secondary amine organocatalyst, wherein three reactions take place in one pot to provide cyclohexene carbaldehydes bearing four stereogenic centers with excellent stereocontrol. This triggered our interest to develop new organocatalytic domino sequences, especially for multiple domino reactions. After our seminal contribution, domino reactions catalyzed by secondary amine organocatalysts not only became more popular, but they also could be catalyzed by other classes of organocatalysts, such as bifunctional hydrogen bonding catalysts, chiral Brønsted acids, and N-heterocyclic carbenes. The mode of activation in this triple domino reaction relied on the sequential generation of enamine and iminium intermediates using a proline-based chiral secondary amine organocatalyst. By employing this strategy, we have developed several triple domino reactions leading to the formation of carbo- and heterocyclic structures bearing multiple stereogenic centers with excellent levels of stereoselectivities. The applications of the secondary amine organocatalysts have been further extended to more complex quadruple domino sequences. Moreover, these multiple domino sequences have been combined successfully with other transformations in one pot to create densely functionalized polycyclic compounds. This Account gives an overview of our research in the area of organocatalytic asymmetric multiple domino reactions with special emphasis on the secondary amine catalyzed triple and quadruple domino reactions via a sequential generation of enamine and iminium intermediates. The multiple cascade reactions assisted by di- and tri-iminium and -enamine species as well as other types of organocatalysts have been excluded from the scope of this Account.

Efficient construction of biologically important functionalized polycyclic spiro-fused carbocyclicoxindoles via an asymmetric organocatalytic quadruple-cascade reaction

A cascade organocatalysis has been developed for the asymmetric synthesis of a highly functionalized polycyclic spiro-fused carbocyclicoxindoles containing five contiguous stereogenic centers with good diastereoselectivity and high enantioselectivity.

α,α-Dicyanoolefins: versatile substrates in organocatalytic asymmetric transformations

α,α-Dicyanoolefins have emerged as versatile reactants, finding use as vinylogous nucleophiles, Michael acceptors and dienophiles in a variety of organic reactions.

Enantioselective Synthesis of Functionalized Polycarbocycles via a Three-Component Organocascade Quadruple Reaction

An efficient organocascade quadruple reaction was conducted to synthesize a functionalized spiropolycyclic scaffold in high chemical yields (43-80%) and excellent levels of stereoselectivity (up to >19:1 dr and 99% ee). The quadruple reaction proceeded smoothly between 1,3-indanedione and aromatic aldehydes with concomitant desymmetrization of prochiral 4-substituted cyclohexanones through the Knoevenagel/Michael/aldol/aldol reaction sequence catalyzed by a bifunctional thiourea catalyst. Two of the formed products were transformed into spirocyclic epoxides containing four contiguous quaternary centers.

Asymmetric synthesis of highly functionalized tetrahydropyrans via a one-pot organocatalytic Michael/Henry/ketalization sequence

A diastereo- and enantioselective Michael/Henry/ketalization sequence to functionalized tetrahydropyrans is described. The multicomponent cascade reaction uses acetylacetone or β-keto esters, β-nitrostyrenes, and alkynyl aldehydes as substrates affording tetrahydropyrans with five contiguous stereocenters. Employing a bifunctional quinine-based squaramide organocatalyst, the title compounds are obtained in moderate to good yields (27-80%), excellent enantiomeric excesses (93-99% ee), and high diastereomeric ratios (dr > 20:1) after one crystallization.