Porous heterogeneous catalysts play a pivotal role in the chemical industry. Herein a new Hf-based metal–organic framework (Hf-NU-1000) incorporating Hf6 clusters is reported. It demonstrates high catalytic efficiency for the activation of epoxides, facilitating the quantitative chemical fixation of CO2 into five-membered cyclic carbonates under ambient conditions, rendering this material an excellent catalyst. As a multifunctional catalyst, Hf-NU-1000 is also efficient for other epoxide activations, leading to the regioselective and enantioretentive formation of 1,2-bifuctionalized systems via solvolytic nucleophilic ring opening.

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A hafnium-based metal-organic framework as an efficient and multifunctional catalyst for facile CO2 fixation and regioselective and enantioretentive epoxide activation.

An efficient Mn-catalyzed aerobic oxidative hydroxyazidation of olefins for synthesis of β-azido alcohols has been developed. The aerobic oxidative generation of azido radical employing air as the terminal oxidant is disclosed as the key process for this transformation. The reaction is appreciated by its broad substrate scope, inexpensive Mn-catalyst, high efficiency, easy operation under air, and mild conditions at room temperature. This chemistry provides a novel approach to high value-added β-azido alcohols, which are useful precursors of aziridines, β-amino alcohols, and other important N- and O-containing heterocyclic compounds. This chemistry also provides an unexpected approach to azido substituted cyclic peroxy alcohol esters. A DFT calculation indicates that Mn catalyst plays key dual roles as an efficient catalyst for the generation of azido radical and a stabilizer for peroxyl radical intermediate. Further calculation reasonably explains the proposed mechanism for the control of C-C bond cleavage or for the formation of β-azido alcohols.

Mn-Catalyzed Highly Efficient Aerobic Oxidative Hydroxyazidation of Olefins: A Direct Approach to β-Azido Alcohols

Direct oxidative conversion of aldehydes and alcohols to 2-imidazolines and 2-oxazolines using molecular iodine

Tandem catalytic systems, often inspired by biological systems, offer many advantages in the formation of highly functionalized small molecules. Herein, a new metal-organic framework (MOF) with porphyrinic struts and Hf6 nodes is reported. This MOF demonstrates catalytic efficacy in the tandem oxidation and functionalization of styrene utilizing molecular oxygen as a terminal oxidant. The product, a protected 1,2-aminoalcohol, is formed selectively and with high efficiency using this recyclable heterogeneous catalyst. Significantly, the unusual regioselective transformation occurs only when an Fe-decorated Hf6 node and the Fe-porphyrin strut work in concert. This report is an example of concurrent orthogonal tandem catalysis.

A Hafnium-Based Metal-Organic Framework as a Nature-Inspired Tandem Reaction Catalyst.

The Lewis acid-promoted reactions of alkyl azides with ketones can afford several products. Chief among these result from a Schmidt-like insertion of the azide into the carbon−carbon bond adjacent to the carbonyl group. Alternatively, an acid-promoted rearrangement of the azide to an iminium species can occur, mostly with benzylic azides; the iminium species can then be trapped by the enol of the carbonyl compound in a variation of the Mannich reaction. The scope of each of these reactions, the dependence of the observed products upon azide and ketone structure, and the nature of acid promotion are discussed. In broad strokes, cyclohexanones and other cyclic ketones react in the presence of TiCl4 to afford insertion products, whereas the Mannich route predominates when benzyl azide and triflic acid are used. The features that lead to each reaction type and possible mechanistic implications are discussed.

Reactions of Alkyl Azides and Ketones as Mediated by Lewis Acids: Schmidt and Mannich Reactions Using Azide Precursors

The reactions of 1,2- and 1,3-hydroxy azides with aldehydes under acidic conditions were examined. A variety of Lewis acids were examined, of which BF3·OEt2 was found the most convenient. Trimethylsilyl ether derivatives of the alcohols could also be reacted using trimethylsilyl triflate as the promoter. Twenty-five examples that proceed in moderate to quantitative yields are reported.

Jennifer G. Badiang

Papers

One-Step Conversion of Aldehydes to Oxazolines and 5,6-Dihydro-4H-1,3-oxazines Using 1,2- and 1,3-Azido Alcohols

One-Step Conversion of Aldehydes to Oxazolines and 5,6-Dihydro-4H-1,3- oxazines Using 1,2- and 1,3-Azido Alcohols.