Cascade Conjugate Research Articles

Formal [4 + 2] Annulation of Oxindole-Embedded ortho-Quinone Methides with 1,3-Dicarbonyls: Synthesis of Spiro[Chromen-4,3'-Oxindole] Scaffolds.

The oxindole-embedded ortho-quinone methides were employed as reactive intermediates in formal [4 + 2] annulation with 1,3-dicarbonyls, providing an efficient access to spiro[chromen-4,3'-oxindole] scaffolds via a cascade conjugate addition/ketalization/dehydration process. This protocol featured metal-free conditions, wide substrate scope, and excellent yields.

Organocatalytic Asymmetric Conjugate Addition and Cascade Acyl Transfer Reaction of α-Nitroketones

Organocatalytic asymmetric conjugate addition of α-nitroketones to β,γ-unsaturated α-keto esters has been developed. A pyrrolidine-based thiourea-tertiary amine was identified as the best catalyst. The reaction was found to proceed via cascade conjugate addition and acyl transfer reaction. A number of α-nitroketones and β,γ-unsaturated α-keto esters were examined in this transformation. 5-Nitro-2-acyloxypent-2-enoates were obtained in good yields (up to 99%) and enantioselectivities (up to 99% ee). The products could be hydrolyzed to provide 5-nitro-2-oxopentanoates, which are not available from the direct addition of nitromethane to β,γ-unsaturated α-keto esters.

Organocatalytic Conjugate Addition of Malononitrile to Conformationally Restricted Dienones

Organocatalytic conjugate addition of malononitrile to conformationally restricted dienones has been studied. A series of chiral primary and tertiary amine catalysts were screened. A piperidine-based thiourea-tertiary amine was found to be the efficient catalyst. Chiral pyran derivatives were obtained in excellent yields and enantioselectivities via a cascade conjugate addition-intramolecular cyclization pathway. The reaction is remarkably different for the corresponding reaction of conformationally flexible dienones.

Chemoselective Suzuki Cross-Coupling Reactions of Chiral Pyrrolizines

Recently, we reported that the enantio- and diastereo-selective organocatalytic cascade conjugate addition-aldol re-actions of a series of 2-trifluoroacetylpyrroles to α,β-unsaturated aldehydes afford highly functionalized chiral pyrrolizines that bear a trifluoromethyl group at the stereogenic center in good yields, high enantioselectivities, and excellent diastereoselec-tivities.

ChemInform Abstract: Organocatalytic Asymmetric Synthesis of Chiral Pyrrolizines by Cascade Conjugate Addition—Aldol Reactions.

As the first N-centered heteroaromatic nucleophile for organocatalytic cascade reactions, pyrroles underwent the enantio- and diastereoselective organocatalytic cascade conjugate addition-aldol reactions of α,β-unsaturated aldehydes that afford the highly functionalized chiral pyrrolizines bearing three consecutive stereocenters in good yields, high enantioselectivities (90-98% ee), and excellent diastereoselectivities (>20:1 dr in all cases).

Organocatalytic Asymmetric Synthesis of Chiral Pyrrolizines by Cascade Conjugate Addition−Aldol Reactions

As the first N-centered heteroaromatic nucleophile for organocatalytic cascade reactions, pyrroles underwent the enantio- and diastereoselective organocatalytic cascade conjugate addition-aldol reactions of α,β-unsaturated aldehydes that afford the highly functionalized chiral pyrrolizines bearing three consecutive stereocenters in good yields, high enantioselectivities (90-98% ee), and excellent diastereoselectivities (>20:1 dr in all cases).

Total Synthesis of (−)-Lycorine and (−)-2-epi-Lycorine by Asymmetric Conjugate Addition Cascade

Total syntheses of (-)-lycorine and (-)-2-epi-lycorine were accomplished using chiral ligand-controlled asymmetric cascade conjugate addition methodology, which enables the formation of two C-C bonds and three stereogenic centers in one pot to give synthetically useful chiral cyclohexane derivatives.

A cascadic conjugate gradient algorithm for mass conservative, semi‐implicit discretization of the shallow water equations on locally refined structured grids

AbstractA semi‐implicit, mass conservative discretization scheme is applied to the two‐dimensional shallow water equations on a hierarchy of structured, locally refined Cartesian grids. Different resolution grids are fully interacting and the discrete Helmholtz equation obtained from the semi‐implicit discretization is solved by the cascadic conjugate gradient method. A flux correction is applied at the interface between the coarser and finer discretization grids, so as to ensure discrete mass conservation, along with symmetry and diagonal dominance of the resulting matrix. Two‐dimensional idealized simulations are presented, showing the accuracy and the efficiency of the resulting method. Copyright © 2002 John Wiley & Sons, Ltd.

The cascadic multigrid method for elliptic problems

The paper deals with certain adaptive multilevel methods at the confluence of nested multigrid methods and iterative methods based on the cascade principle of [10]. From the multigrid point of view, no correction cycles are needed; from the cascade principle view, a basic iteration method without any preconditioner is used at successive refinement levels. For a prescribed error tolerance on the final level, more iterations must be spent on coarser grids in order to allow for less iterations on finer grids. A first candidate of such a cascadic multigrid method was the recently suggested cascadic conjugate gradient method of [9], in short CCG method, whichused the CG method as basic iteration method on each level. In [18] it has been proven, that the CCG method is accurate with optimal complexity for elliptic problems in 2D and quasi-uniform triangulations. The present paper simplifies that theory and extends it to more general basic iteration methods like the traditional multigrid smoothers. Moreover, an adaptive control strategy for the number of iterations on successive refinement levels for possibly highly non-uniform grids is worked out on the basis of a posteriori estimates. Numerical tests confirm the efficiency and robustness of the cascadic multigrid method.