Cascade (domino) reactions have an unparalleled ability to generate molecular complexity from relatively simple starting materials; these transformations are particularly appealing when multiple rings are forged during this process. In this tutorial review, we cover recent highlights in cascade polycyclizations as applied to natural product synthesis, including pericyclic, heteroatom-mediated, cationic, metal-catalyzed, organocatalytic, and radical sequences.

The stereochemical role of the phosphoramidite ligand in the asymmetric conjugate addition of alkylzirconium species to cyclic enones has been established through experimental and computational studies. Systematic, synthetic variation of the modular ligand established that the configuration of the binaphthol backbone is responsible for absolute stereocontrol, whereas modulation of the amido substituents leads to dramatic variations in the level of asymmetric induction. Chiral amido substituents are not required for enantioselectivity, leading to the discovery of a new family of easily synthesized phosphoramidites based on achiral amines that deliver equal levels of selectivity to Feringa's ligand. A linear correlation between the length of the aromatic amido groups and experimentally determined enantioselectivity was uncovered for this class of ligand, which, following an optimisation, leading to the highly selective ligands (up to 94% ee) with naphthyl rather than phenyl groups. An electronic effect of sterically similar aromatic substituents was investigated through NMR and DFT studies, showing that electron rich aryl groups allow better Cu-coordination. An interaction between the metal center and an aromatic group is responsible for this enhanced affinity and leads to a more tightly-coordinated transition structure leading to the major enantiomer. These studies illustrate the use of parametric quantitative structure-selectivity relationships to generate mechanistic models for asymmetric induction and catalyst structures that may be further probed by experiment and computation. This integrated approach leads to the rational modification of chiral ligands to achieve enhanced levels of selectivity.

A new asymmetric conjugate addition method was developed for β-substituted cyclopentenones to form quaternary centres using alkylzirconocene nucleophiles giving up to 97% yield and 92% ee.

Understanding how catalytic asymmetric reactions with racemic starting materials can operate would enable new enantioselective cross coupling reactions giving chiral products. Here we propose a catalytic cycle for the highly enantioselective Rh(I)-catalysed Suzuki-Miyaura coupling of boronic acids and racemic allyl halides. Natural abundance 13 C kinetic isotope effects provide quantitative information about the transition state structures of two key elementary steps in the catalytic cycle -transmetalation and oxidative addition. Experiments using configurationally stable, deuterium labelled substrates reveal oxidative addition can happen via syn-or antipathways which controls diastereoselectivity. DFT calculations attribute the extremely high enantioselectivity to reductive elimination from a common Rh complex formed from both allyl halide enantiomers. Our conclusions are supported by analysis of the reaction kinetics. These insights into the sequence of bond-forming steps and their transition state structures will contribute to understanding asymmetric Rh-allyl chemistry and enable the discovery and application of asymmetric reactions with racemic substrates.

Psoralen derivatives are well known for their unique phototoxicity and also exhibits promising anti-breast cancer activity both in the presence and the absence of UVA irradiation. However, the structure–activity relationship on this scaffold remains lacking. Herein, a series of psoralen derivatives with various C-5 substituents were synthesized and evaluated for their in vitro dark and light-activated cytotoxicity against three breast cancer cell lines: MDA-MB-231, T47-D, and SK-BR-3. The type of substituents dramatically impacted the activity, with the 4-bromobenzyl amide derivative (3c) exhibiting the highest dark cytotoxicity against T47-D (IC50 = 10.14 µM), with the activity comparable to those of the reference drugs (doxorubicin, 1.46 µM; tamoxifen citrate, 20.86 µM; lapatinib 9.78 µM). On the other hand, the furanylamide 3g exhibits the highest phototoxicity against SK-BR-3 cells with the IC50 of 2.71 µM, which is almost tenfold increase compared to the parent compound, methoxsalen. Moreover, these derivatives showed exceptional selectivity towards HER2+ (SK-BR-3) over the HER2− (MDA-MB-231) breast cancer cell lines, which correlates well with the results from the molecular docking study, revealing that 3g formed favorable interactions within the active site of the HER2. Additionally, the cell morphology of SK-BR-3 cells suggested that the significant phototoxicity was related to induction of cell apoptosis. Most of the synthesized psoralen derivatives possess acceptable physicochemical properties and are suitable for being further developed as a novel anti-breast cancer agent in the future.

A mechanism for Rh(I)-catalyzed asymmetric Suzuki-Miyaura coupling with racemic allyl halides is proposed based on a combination of experimental studies and quantum chemical calculations. <br>

No abstract

A mechanism for Rh(I)-catalyzed asymmetric Suzuki-Miyaura coupling with racemic allyl halides is proposed based on a combination of experimental studies and quantum chemical calculations. <br>