This Microreview illustrates the conceptual evolution of Pauson-Khand-type reactions and the recent advancements in catalyst design and applications. Intra-and intermolecular Pauson-Khand-type reactions, as well as their enantioselec-

Aryl mesylates are found to be applicable as electrophiles in organosilicon-mediated coupling reactions. The catalyst system comprising 2 mol % of Pd(OAc)(2) and CM-phos supporting ligand is highly effective in catalyzing Hiyama cross-coupling of various aryl and heteroaryl mesylates. Interesting acid additive effects show that the presence of 0.25-0.50 equiv of acetic acid efficiently suppresses the mesylate decomposition and generally promotes the coupling product yields.

Here, a novel colorimetric sensing platform for highly selective detection of Fe 3+ in aqueous solutions was developed based on zero-dimensional Zn-MOF-74 [Zn 2 (DOBDC), DOBDC = 2,5-dihydroxyterephthalic acid] nanodots. The first ultrasmall Zn-MOF-74 nanodots with the average size within 10 nm were successfully synthesized by manipulating the initial conditions with a diluted material system. It was found that the ultrasamll MOF nanodots had a highly selective interaction with Fe 3+ and showed a specific blue colorimetric change in aqueous solution. The highly dispersive nature in aqueous solution and high surface-to-volume ratio help MOF-74 nanodots closely interact with the targeted Fe 3+ ions with a low limit of detection of 1.04 μM and a fast response within seconds. Finally, we demonstrate that the selective Fe 3+ sensing mechanism of Zn-MOF-74 nanodots is due to the selective framework disruption and the formation of Fe-DOBDC salt complex with blue color. It is the first report of nanoscale MOF based colorimetric Fe 3+ sensor with low limit of detection (LOD) comparable even to fluorescent MOF based Fe 3+ sensors, which could be easily observed by naked-eye without expensive fluorescence apparatuses. The good colorimetric stability in aqueous environment, low limit of detection, rapid response, and nanosize nature enable this MOF nanodot to be a good Fe 3+ sensing probe for biological and environmental sensing applications.

They make a good couple: Catalysts generated from Pd(OAc)2 and indolylphosphine ligands are highly effective in the titanium‐mediated coupling of aryl halides. Catalyst loadings as low as 0.05 mol % Pd can be used. The mild reaction conditions also allow the coupling of aryl sulfonyl chlorides with aryl titanium reagents to generate diaryl sulfones.

We describe highly enantioselective synthesis of ␤-amino acid derivatives (1a-c) using asymmetric hydrogenation of ␣-aminomethylacrylates (2a-c), which contain a free basic NOH group, as the key step. The ␣-aminomethylacrylates (2a-c) were prepared using the BaylisHillman reaction of an appropriate aldehyde with methyl acrylate followed by acetylation of the resulting allylic alcohols (4a-b) and S N2 -type amination of the allylic acetates (3a-b).asymmetric catalysis ͉ Baylis-Hillman reaction I n recent years, ␤-amino acids have received increasing attention as constituents of molecules with interesting biological and pharmacological activities (1-5) such as hypoglycemic and ketogenic activities. They are key moieties of a number of bioactive molecules, such as in taxol and in peptidic natural products with various enzyme inhibiting activities. Nonpeptidic ␤-amino acids are found in well known ␤-lactams. Considering their importance, asymmetric synthesis of enantiomerically pure ␤-amino acids has become an important challenge for organic chemists. The synthesis of enantiopure ␤-amino acids has been extensively studied (6-9). However, the known methods are mostly for the synthesis of ␤-substituted ␤-amino acids, and their preparation still suffers from a long synthetic sequence, low product yields, and laborious execution (10-14). For example, a recently reported synthesis of 1a involved nine steps from 3-phenylpropanoic acid (15-18). Peptide deformylase (PDF, EC 3.5.1.31), a metallopeptidase found in prokaryotic organisms, is essentially required for bacterial growth (19)(20)(21). Certain N-formyl hydroxylamine compounds were recently revealed to have good antibacterial function by means of their PDF-inhibiting capabilities. Chiral compounds 1, ␣-substituted ␤-amino acid derivatives, are key intermediates in the synthesis of this kind of compounds (15)(16)(17)(18)22). Their prochiral dehydroprecursors 2 could be prepared in high yields via a synthetic process shown in Scheme 1. Asymmetric hydrogenation of these substrates 2 is the simplest and most direct route to synthesize 1 because of its inherent efficiency and atom economy. In contrast to the great progress in the synthesis of ␤-substituted ␤-amino acids and derivatives via enantioselective hydrogenations (23-38), reports on the synthesis of ␣-substituted ␤-amino acids with this protocol are very limited. To the best of our knowledge, only one exceptional example has been given, very recently by Zheng and coworkers (38), using Rh-monophosphorus catalyst system for the hydrogenation of ␤-phthalimide acrylates. However, the activity of the catalyst was not high, and only E-isomers of substituted ␤-phthalimide acrylates were investigated. In fact, compounds 2 were a mixture of E-and Z-isomers formed in the synthesis, and they were not always easy to separate into single isomers. Generally, it is also difficult to achieve high activity and enantioselectivity for the system containing both isomers (23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33). In light of the suc...