Metal-free oxidative cross-coupling of diazirines with arylboronic acids

Reactions of Frustrated Lewis Pairs with Chloro-Diazirines: Cleavage of N=N Double Bonds

The reactions of FLPs with diazomethanes leads to the rapid loss of N2 . In contrast, in this work, we reported reactions of phosphine/borane FLPs with chlorodiazirines which led to the reduction of the N=N double bond, affording linked phosphinimide/amidoborate zwitterions of the general form R3 PNC(Ar)NR'BX(C6 F5 )2 . A detailed DFT mechanistic study showed that these reactions proceed via FLP addition to the N=N bond, followed by subsequent group transfer reactions to nitrogen and capture of the halide anion.

Biocatalytic Carbene Transfer Using Diazirines

Biocatalytic carbene transfer from diazo compounds is a versatile strategy in asymmetric synthesis. However, the limited pool of stable diazo compounds constrains the variety of accessible products. To overcome this restriction, we have engineered variants of Aeropyrum pernix protoglobin (ApePgb) that use diazirines as carbene precursors. While the enhanced stability of diazirines relative to their diazo isomers enables access to a diverse array of carbenes, they have previously resisted catalytic activation. Our engineered ApePgb variants represent the first example of catalysts for selective carbene transfer from these species at room temperature. The structure of an ApePgb variant, determined by microcrystal electron diffraction (MicroED), reveals that evolution has enhanced access to the heme active site to facilitate this new-to-nature catalysis. Using readily prepared aryl diazirines as model substrates, we demonstrate the application of these highly stable carbene precursors in biocatalytic cyclopropanation, N-H insertion, and Si-H insertion reactions.

Base Mediated Diazirination via Iodine(III) Reagents

Herein, we described an efficient method for the construction of highly functionalized diazirines from the carbohydrazide and diazo-substituted hypervalent iodine reagents. Unambiguous transformation has been designed with user applicable and easy practicable conditions. Remarkably, d-glucose, menthol, aspirin, proline, and lithocholic acid were efficiently diazirinated. Furthermore, the method is mild, robust, and highly selective, which successfully converted a variety of aryl, alkyl, benzyl, and heterocyclic hydrazides into the corresponding diazirine derivatives.

Brønsted acid-catalyzed homogeneous O–H and S–H insertion reactions under metal- and ligand-free conditions

The economical and accessible CF₃SO₃H successfully catalyzed homogeneous O–H and S–H bond insertion reactions between hydroxyl compounds, thiols and diazo compounds under metal- and ligand-free conditions.

Iodonitrene in Action: Direct Transformation of Amino Acids into Terminal Diazirines and 15N2-Diazirines and Their Application as Hyperpolarized Markers

A one-pot metal-free conversion of unprotected amino acids to terminal diazirines has been developed using phenyliodonium diacetate (PIDA) and ammonia. This PIDA-mediated transformation occurs via three consecutive reactions and involves an iodonitrene intermediate. This method is tolerant to most functional groups found on the lateral chain of amino acids, it is operationally simple, and it can be scaled up to provide multigram quantities of diazirine. Interestingly, we also demonstrated that this transformation could be applied to dipeptides without racemization. Furthermore, ¹⁴N₂ and ¹⁵N₂ isotopomers can be obtained, emphasizing a key trans-imination step when using ¹⁵NH₃. In addition, we report the first experimental observation of ¹⁴N/¹⁵N isotopomers directly creating an asymmetric carbon. Finally, the ¹⁵N₂-diazirine from l-tyrosine was hyperpolarized by a parahydrogen-based method (SABRE-SHEATH), demonstrating the products' utility as hyperpolarized molecular tag.

Reducing Limitation in Probe Design: The Development of a Diazirine-Compatible Suzuki-Miyaura Cross Coupling Reaction

Access to high quality photoaffinity probe molecules is often constrained by synthetic limitations related to diazirine installation. A survey of recently published photoaffinity probe syntheses identified the Suzuki-Miyaura (S-M) coupling reaction, ubiquitous in drug discovery, as being underutilized to incorporate diazirines. To test whether advances in modern cross-coupling catalysis might enable efficient S-M couplings tolerant of the diazirine moiety, a fragment-based screening approach was employed. A model S-M coupling reaction was screened under various conditions in the presence of an aromatic diazirine fragment. This screen identified reaction conditions that gave good yields of S-M coupling product while minimally perturbing the diazirine reporter fragment. These conditions were found to be highly scalable and exhibited broad scope when applied to a chemistry informer library of 24 pharmaceutically relevant aryl boron pinacol esters. Furthermore, these conditions were used to synthesize a known diazirine-containing probe molecule with improved synthetic efficiency.