Photoredox-Catalyzed Synthesis of Alkylaryldiazenes: Formal Deformylative C-N Bond Formation with Alkyl Radicals.

Diazenes are valuable compounds that have found broad applicability because of their optical and biological properties. We report the synthesis of alkylaryldiazenes via formal, photoredox-catalyzed, deformylative C-N bond formation. The procedure employs dihydropyridines for the generation of alkyl radicals, which are then trapped by diazonium salts and reduced to the corresponding diazenes. Control experiments were performed to confirm the involvement of radicals in the mechanism. The reaction can be carried out at room temperature and employs readily available reagents; the mild conditions allowed the use of highly functionalized substrates. There was no observed tautomerization of the diazenes to the corresponding arylhydrazones.

Hydrogen Bonding: Regulator for Nucleophilic Fluorination.

The recent advances in nucleophilic fluorination, regulated through hydrogen bonding interactions are summarized. Two main categories of fluorine nucleophiles are discussed. Alkali-metal fluorides are widely used in various fluorination transformations because they are inexpensive and safe nucleophilic fluorine sources. But the non-controllable nucleophilicity and strong basicity of some of them cause undesired side reactions, which led to the introduction of hydrogen bonding to fine tune their nucleophilicity and basicity. In contrast, an HF-based fluorine nucleophile, HF/DMPU, is in some aspects superior to the conventional HF/pyridine (Olah's reagent) or HF/Et3 N because of the higher hydrogen bond basicity of DMPU. It has been used in several nucleophilic fluorinations such as fluorination of alkynes, fluoro-Prins reaction and fluorination of aziridines.

Bromofluorination of Unsaturated Compounds using DMPU/HF as a Fluorinating Reagent.

Bromofluorination reactions were performed by treating of a variety of unsaturated compounds with N-bromosuccinimide (NBS) and DMPU/HF as the fluorinating reagent. The DMPU/HF complex showed to be an efficient fluorinating reagent to convert alkenes into their corresponding bromofluoro compounds. It showed to have high reactivity and the process afforded bromofluorinated products with good Markovnikov regioselectivity. These fluorinated compounds are useful starting materials and serve as building blocks for many fluorinated biologically active molecules.

Synthesis of Alkyl Halides from Aldehydes via Deformylative Halogenation.

An unprecedented deformylative halogenation of aldehydes to alkyl halides is presented. Under oxidative conditions, 1,4-dihydropyridine (DHP), derived from an aldehyde, generated a C(sp3)- radical that coupled with a halogen radical that was generated from inexpensive and atom-economical halogen sources (NaBr, NaI, or HCl), to yield an alkyl halide. Because of the mild conditions, a wide range of functional groups were tolerated, and excellent site selectivity was achieved.

Metal-free Regioselective Hydrochlorination of Unactivated Alkenes via a Combined Acid Catalytic System.

A combined acid HCl/DMPU-acetic acid catalytic system was used in the hydrochlorination of a wide range of unactivated alkenes. This hydrochlorination strategy is remarkably greener than previous reported methods in terms of high atom efficiency, no toxic waste generated and metal-free process. The higher efficiency, compared with other commercially available HCl reagents, was augmented by the good regioselectivity and functionality tolerance found. A stepwise mechanism for this hydrochlorination process was proposed based on kinetic studies.

A Chlorinating Reagent Yields Vinyl Chlorides with High Regioselectivity under Heterogeneous Gold Catalysis.

A novel chlorinating reagent with a high concentration of HCl has enabled the highly regioselective hydrochlorination of unactivated alkynes using a commercial nanogold catalyst. No overchlorination or hydration products were formed, and various functional groups were tolerated. This hydrochlorination method could be conducted under open air.

Chloride-Tolerant Gold(I)-Catalyzed Regioselective Hydrochlorination of Alkynes.

We have developed a highly regioselective homogeneous gold(I)-catalyzed anti-hydrochlorination of unactivated alkynes at room temperature. We have overcome the incompatibility between conventional cationic gold catalysts and chloride by using a hydrogen-bonding activation of the Au-Cl bond. This approach is scalable, exhibits excellent functional group tolerance, and can be conducted in open air.

Supported gold nanoparticles catalyzed cis-selective semihydrogenation of alkynes using ammonium formate as the reductant.

TiO2 supported gold nanoparticles with low loading (0.5 mol%) are able to semihydrogenate non-fluorinated and gem-difluorinated alkynes to cis-alkenes with high selectivity, using cost-effective and easy-to-handle ammonium formate as the reductant. No over-reduction was observed. The good recyclability of Au/TiO2 allows for "green" semireduction of alkynes. A difluorinated pyran and α,ß-unsaturated δ-lactone were easily prepared from the obtained gem-difluoro alkene building blocks.

Efficient hydration of alkynes through acid-assisted Brønsted acid catalysis.

The combined acid catalyzed hydration of alkynes is an efficient one-step synthesis of carbonyl compounds. This atom-economical method is effective with a wide range of substrates, and the products are obtained in very good yields with low catalyst loading (0.2%). Furthermore, solid acids like Nafion were also efficient and could be easily recycled multiple times without loss of reactivity.

Supported gold nanoparticle-catalyzed hydration of alkynes under basic conditions.

TiO2-supported nanosize gold particles catalyze the hydration of alkynes using morpholine as a basic cocatalyst. Unlike most homogeneous cationic gold catalysts, the TiO2-Au/morpholine system is weakly basic and is compatible with acid-sensitive functional groups (e.g., silyl ethers, ketals) or with a strongly coordinating group such as pyridine. What's more, this gold catalyst can be recycled by simple filtration and works well in flow reactors.

Synthesis, characterization and in vitro antiproliferative activities of new 13-cis-retinoyl ferrocene derivatives.

In order to improve biological behavior of the retinoyl derivatives, monoarylferrocenyl alcohols 9a and 9b were synthesized by an improved Suzuki cross-coupling method and their 13-cis-retinoic acid analogues were prepared in moderate to good yields via the Mitsunobu reaction. Their structures were confirmed by IR, (1)H NMR, (13)CNMR, MS spectra and element analysis and their antiproliferative activities were determined in vitro using human cancer cell lines. The results of bioassay showed that these organometallic analogues exhibited higher antiproliferative activities than parent 13-cis-retinoic acid and other retinoyl derivatives.