Catalyst-free inverse-electron-demand aza-Diels-Alder reaction of 4,4-dicyano-2-methylenebut-3-enoates and 1,3,5-triazinanes: access to polysubstituted tetrahydropyridines

An inverse-electron-demand aza-Diels-Alder reaction between 4,4-dicyano-2-methylenebut-3-enoates and 1,3,5-triazinanes under catalyst-free and additive-free conditions was developed, which provided a highly convenient and straightforward method to construct a series of polyfunctionalized tetrahydropyridines in high yields. This strategy features numerous advantages, including high efficiency, good functional group tolerance, broad substrate scope, and environmentally friendly conditions.

Functionalized Cyclopentenes via the Formal [4+1] Cycloaddition of Photogenerated Siloxycarbenes from Acyl Silanes

This work describes the first formal cycloaddition reaction of photogenerated nucleophilic carbenes derived from acylsilanes with electrophilic dienes. The resulting transient donor-acceptor cyclopropane rearranges to its stable and highly functionalized cyclopentene isomer in an unprecedented metal-free process. The cyclopropanation-vinyl cyclopropane rearrangement sequence was corroborated by computational calculations. The cyclopropane formation corresponds to a higher energetic barrier, and the vinylcyclopropane-cyclopentene rearrangement proceeds through different mechanisms, although of comparable energies, depending on the stereochemistry of the cyclopropane.

Phosphine-catalyzed divergent reactivity of alkynoates with acid anhydrides: chemo- and stereoselective synthesis of polysubstituted olefins and dienes

Unprecedented phosphine-catalyzed chemoselective acylesterification, tandem addition and Michael type reaction between alkynoates and acid anhydrides have been developed, enabling efficient synthesis of either the polysubstituted olefins or the multifunctional dienes.

Benchmarking the inversion barriers in σ3λ3-phosphorus compounds: a computational study

Benchmark study of three mechanisms for inversion at phosphorus, including parametric criteria for classification and analysis of factors affecting barriers.

Phosphine Organocatalysis

The hallmark of nucleophilic phosphine catalysis is the initial nucleophilic addition of a phosphine to an electrophilic starting material, producing a reactive zwitterionic intermediate, generally under mild conditions. In this Review, we classify nucleophilic phosphine catalysis reactions in terms of their electrophilic components. In the majority of cases, these electrophiles possess carbon-carbon multiple bonds: alkenes (section 2), allenes (section 3), alkynes (section 4), and Morita-Baylis-Hillman (MBH) alcohol derivatives (MBHADs; section 5). Within each of these sections, the reactions are compiled based on the nature of the second starting material-nucleophiles, dinucleophiles, electrophiles, and electrophile-nucleophiles. Nucleophilic phosphine catalysis reactions that occur via the initial addition to starting materials that do not possess carbon-carbon multiple bonds are collated in section 6. Although not catalytic in the phosphine, the formation of ylides through the nucleophilic addition of phosphines to carbon-carbon multiple bond-containing compounds is intimately related to the catalysis and is discussed in section 7. Finally, section 8 compiles miscellaneous topics, including annulations of the Hüisgen zwitterion, phosphine-mediated reductions, iminophosphorane organocatalysis, and catalytic variants of classical phosphine oxide-generating reactions.

Direct β-selectivity of α,β-unsaturated γ-butyrolactam for asymmetric conjugate additions in an organocatalytic manner

The β-selective asymmetric addition of γ-butyrolactam with cyclic imino esters catalyzed by a bifunctional chiral tertiary amine has been developed, which provides an efficient access to optically active β-position functionalized pyrrolidin-2-one derivatives in both high yield and enantioselectivity (up to 78% yield and 95 : 5 er). This is the first catalytic method to access chiral β-functionalized pyrrolidin-2-one via a direct organocatalytic approach.

Asymmetric Organocatalytic One-Pot, Two-Step Sequential Process to Synthesize Chiral Acetal-Containing Polycyclic Derivatives from Cyclic Hemiacetals and Enones

We have developed an efficient one-pot, two-step sequential process to synthesize biologically and synthetically important chiral acetal-containing polycyclic derivatives. This novel protocol had been proved to proceed via Michael-lactolization-oxocarbenium ion ring-closing sequence, which was initiated by a key reactive enamine intermediate and interrupted the previously established reaction pathway of two different enones used in this work, and generated the corresponding cycloadducts with excellent stereoselectivity bearing up to seven continuous stereocenters. Both chiral and racemic starting cyclic hemiacetals worked well in this strategy. The synthetic applications of the obtained polycyclic products have also been demonstrated.

Asymmetric cycloaddition reactions catalysed by diarylprolinol silyl ethers

Organocatalysis as a paint palette for asymmetric cycloaddition reactions.

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.

Catalytic asymmetric β,γ activation of α,β-unsaturated γ-butyrolactams: direct approach to β,γ-functionalized dihydropyranopyrrolidin-2-ones

Skeleton in the closet: The title reaction enables the development of the first catalytic β,γ-selective Diels-Alder [4+2] annulation of α,β-unsaturated γ-butyrolactams (see scheme; Boc=tert-butoxycarbonyl, Ts=4-toluenesulfonyl). This process provides a direct method for the enantioselective construction of bi- or tricyclic dihydropyranopyrrolidin-2-one skeletons in only one step.

Organocatalytic asymmetric annulation of 1,3-bis(alkoxycarbonyl)buta-1,3-dienes and aldehydes

Asymmetric organocatalytic annulation of E/Z isomeric mixtures of bis(alkyl carboxylate)buta-1,3-dienes and aldehydes has been realized via enamine catalysis. In the presence of α,α-diphenyl-2-pyrrolidinemethanol trimethylsilyl ether, excellent stereo- and enantioselectivities were achieved for a broad spectrum of substrates.

Aminocatalytic asymmetric Diels-Alder reactions via HOMO activation

In the first successful catalytic asymmetric Diels-Alder reaction in 1979, Koga and colleagues used a chiral aluminum complex as a Lewis acid catalyst, but since then, researchers have developed numerous catalytic systems for these reactions. By 2000, several chiral organic compounds, such as the salts of imidazolidinones or TADDOLs, emerged as robust catalysts in the asymmetric Diels-Alder reactions. According to frontier molecular orbital theory, most of these catalysts employ a LUMO-lowering strategy as a means of activating electron-deficient dienophiles. Only rarely do chiral catalysts take advantage of the alternative strategy of activating the HOMO. In this Account we will discuss the development of asymmetric Diels-Alder reactions based on the HOMO-raising effects of chiral amines. First, we show that enamine intermediates formed in situ between an amine catalyst and enolizable aliphatic aldehydes can act as electron-rich dienophiles in inverse-electron-demand Diels-Alder reactions. We describe the preparation of a variety of oxygen- or nitrogen-containing heterocycles with high optical purity. Then, we demonstrate that the dienamine species from α,β-unsaturated aldehydes can act either as electron-rich dienes in normal-electron-demand Diels-Alder reactions or as dienophiles in inverse-electron-demand Diels-Alder reactions. These reactions generally occur with high chemo-, regio-, and stereoselectivity. Finally, we introduce a new activation mode for Diels-Alder reactions, in which reactive trienamine intermediates derived from 2,4-dienals or even 2,4-dienones play a key role. Notably, we observe remarkable β,ε-regioselectivity and obtain excellent stereocontrol even at the very remote ε-reactive center-up to seven bonds away from the chiral center of the amine catalyst. These results demonstrate that a HOMO-activation strategy via aminocatalysis could become a significant tool in asymmetric Diels-Alder reactions. In addition, these reactions using enamine, dienamine, or trienamine intermediates produce a diverse array of densely functionalized cyclic scaffolds, which may serve as valuable structures in drug discovery and natural product synthesis.