Transition metal-free direct nucleophilic α-substitution of Morita–Baylis–Hillman alcohols with amines and thiols

An efficient transition metal-free allylic nucleophilic α-substitution of Morita–Baylis–Hillman alcohols with both aliphatic and aromatic amines in refluxing toluene, using activated molecular sieves as additives, is described herein. The reaction proceeded with exclusive α-regioselectivity in moderate to excellent yields with the formation of water as the sole by-product. Under the same conditions, upon treatment of some thiols with the title substrates, allylic sulfides were obtained in excellent yields and high regioselectivity.     

Gold(I)‐Catalysed Direct Thioetherifications Using Allylic Alcohols: an Experimental and Computational Study

A gold(I)‐catalysed direct thioetherification reaction between allylic alcohols and thiols is presented. The reaction is generally highly regioselective (S_N2′). This dehydrative allylation procedure is very mild and atom economical, producing only water as the by‐product and avoiding any unnecessary waste/steps associated with installing a leaving or activating group on the substrate. Computational studies are presented to gain insight into the mechanism of the reaction. Calculations indicate that the regioselectivity is under equilibrium control and is ultimately dictated by the thermodynamic stability of the products.     

Palladium(II)‐Catalyzed Allylic CH Oxidation of Hindered Substrates Featuring Tunable Selectivity Over Extent of Oxidation

The use of Oxone and a palladium(II) catalyst enables the efficient allylic C? H oxidation of sterically hindered α‐quaternary lactams which are unreactive under known conditions for similar transformations. This simple, safe, and effective system for C? H activation allows for unusual tunable selectivity between a two‐electron oxidation to the allylic acetates and a four‐electron oxidation to the corresponding enals, with the dominant product depending on the presence or absence of water. The versatile synthetic utility of both the allylic acetate and enal products accessible through this methodology is also demonstrated.     

Bacterial Synthesis of Unusual Sulfonamide and Sulfone Antibiotics by Flavoenzyme‐Mediated Sulfur Dioxide Capture

Sulfa drugs, such as sulfonilamide and dapsone, are classical antibiotics that have been in clinical use worldwide. Despite the relatively simple architectures, practically no natural products are known to feature such aromatic sulfonamide or diarylsulfone substructures. We report the unexpected discovery of three fully unprecedented, sulfonyl‐bridged alkaloid dimers (sulfadixiamycins A–C) from recombinant Streptomyces species harboring the entire xiamycin biosynthesis gene cluster. Sulfadixiamycins exhibit moderate antimycobacterial activities and potent antibiotic activities even against multidrug‐resistant bacteria. Gene inactivation, complementation, and biotransformation experiments revealed that a flavin‐dependent enzyme (XiaH) plays a key role in sulfadixiamycin biosynthesis. XiaH mediates a radical‐based, three‐component reaction involving two equivalents of xiamycin and sulfur dioxide, which is reminiscent of radical styrene/SO₂ copolymerization.     

The effect of hydrogen-fluorine defects on the conformational energy of polytrifluoroethylene chains

Conformational energy calculations were employed to determine the effect of hydrogen-fluorine defects on the conformation of the polytrifluoroethylene chain. It was determined that the 3₁ helix was energetically favored for all but the highly syndiotactic polymers, which favored the all-trans conformation. The incorporation of head-to-head linkages into the polymer chain increased the Conformational energy of the 3₁ helix while the Conformational energy of the all-trans form decreased. The energies of these two conformations did not equalize until the head-to-head concentration reached 20 to 30%, depending on the tacticity of the polymer. The trans, gauche, trans, gauche' conformation was also determined to be energetically favorable for the syndiotactic polymer, but both tacticity defects and head-to-head linkages caused a rapid increase in the Conformational energy. This was, therefore, concluded to be unlikely structure when chemical defects are incorporated into the polymer chain.     

Effect of Annealing Treatment on Meta-poly(arylene sulfide sulfone amide)

A useful annealing treatment above glass transition temperature of high molecular weight amorphous m-poly(arylene sulfide sulfone amide) (m-PASSA) was employed in this work. No crystalline or cross-link structures were formed according to X-ray diffraction, differential scanning calorimetry, and nuclear magnetic resonance results; nevertheless, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis results showed that the number of terminal carboxyl groups of annealed m-PASSA decreased after the annealing treatment. The volatiles formed in the decomposition of m-PASSA were investigated by combined thermogravimetric analysis and online FTIR. The initial volatile products in the decomposition experiments supported a process that involved the cleavage of an aromatic carboxyl group, followed by the emission of major volatile products—carbon dioxide, sulfur dioxide, and benzenthiol—released from the amide, sulfone, and diphenyl sulphide groups in m-PASSA. Annealed m-PASSA exhibited different thermal properties, as evidenced by thermogravimetric analysis, compared to the untreated polymer. The degradation activation energy increased from 154.4 kJ/mol to 173.6 kJ/mol after annealing treatment, and the lifetime was extended by more than 1000 times.     

A novel method for the synthesis of aryl trihalomethyl sulfones and their derivatization: the search for new sulfone fungicides

A novel method for the preparation of bioactive aryl trihalomethyl sulfones is reported. An iodination reaction with iodine bromide is applied for the synthesis of difluoroiodomethyl aryl sulfones. A series of difluoroiodomethylsulfonyl group bearing derivatives is afforded, including nitroanilines and benzimidazoles. Biological studies show high fungicidal activity for a number of the synthesized sulfones.