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1. Reactivity of Biomass‐Derived Olefins with Elemental Sulfur: Mechanistic Insight

   https://doi.org/10.1002/ejoc.202301269  

   Kapuge_Dona, Nawoda_L; Maladeniya, Charini_P; Smith, Rhett_C (March 2024, European Journal of Organic Chemistry)

   Abstract Lignocellulosic biomass remains underutilized despite its annual production in gigaton quantities. Sulfur is another vastly underutilized waste product of fossil fuel refining. New mechanistic insight into the reactions of sulfur unveiled since 2020 suggest a rich and hitherto unexplored chemistry between biomass‐derived olefins and elemental sulfur. In this study, four biomass‐derived olefins (eugenol (1), 4‐allyl‐2,6‐dimethoxyphenol (2),o‐eugenol (3), and 2‐allyl‐6‐methylphenol(4)) were reacted with elemental sulfur to elucidate the S−C bond‐forming and other reactivity of these compounds. Each of the compounds was reacted with elemental sulfur in three sulfur : organic reactant ratios (2 : 1, 4 : 1 and 9 : 1) and at two temperatures (180 °C or 230 °C). Product mixtures were characterized using¹H NMR spectrometry and GC‐MS analysis. Products resulting from a range of mechanisms were unveiled, including inverse vulcanization, S−C_{allylic/benzylic}bond formation, S−C_arylbond formation, intramolecular cyclization, C−C σ‐bond scission, and C−O σ‐bond scission. It is anticipated that the insights from this study will support further synergy between the critical sustainability goals of biomass and sulfur utilization. 

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2. Single-Step Replacement of an Unreactive C–H Bond by a C–S Bond Using Polysulfide as the Direct Sulfur Source in the Anaerobic Ergothioneine Biosynthesis

   https://doi.org/https://doi.org/10.1021/acscatal.0c01809  

   Ronghai Cheng, Lian Wu (July 2020, ACS catalysis)

   null (Ed.)

   Ergothioneine, a natural longevity vitamin and antioxidant, is a thiol-histidine derivative. Recently, two types of biosynthetic pathways were reported. In the aerobic ergothioneine biosyntheses, non-heme iron enzymes incorporate a sulfoxide into an sp2 C–H bond from trimethyl-histidine (hercynine) through oxidation reactions. In contrast, in the anaerobic ergothioneine biosynthetic pathway in a green-sulfur bacterium, Chlorobium limicola, a rhodanese domain containing protein (EanB), directly replaces this unreactive hercynine C–H bond with a C–S bond. Herein, we demonstrate that polysulfide (HSSnSR) is the direct sulfur source in EanB catalysis. After identifying EanB’s substrates, X-ray crystallography of several intermediate states along with mass spectrometry results provide additional mechanistic details for this reaction. Further, quantum mechanics/molecular mechanics (QM/MM) calculations reveal that the protonation of Nπ of hercynine by Tyr353 with the assistance of Thr414 is a key activation step for the hercynine sp2 C–H bond in this trans-sulfuration reaction. 

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3. Syntheses and crystal structures of the anhydride 4-oxatetracyclo[5.3.2.0 ^2,6 .0 ^8,10 ]dodec-11-ene-3,5-dione and the related imide 4-(4-bromophenyl)-4-azatetracyclo[5.3.2.0 ^2,6 .0 ^8,10 ]dodec-11-ene-3,5-dione

   https://doi.org/10.1107/S2056989020009512  

   Hulsman, Andrew; Lorenzana, Isabel; Schultz, Theodore; Squires, Breezy; Stenfors, Brock A.; Tolonen, Mason; Staples, Richard J.; Biros, Shannon M.; Winchester, William R. (August 2020, Acta Crystallographica Section E Crystallographic Communications)

   null (Ed.)

   The syntheses and crystal structures of the two title compounds, C 11 H 10 O 3 ( I ) and C 17 H 14 BrNO 2 ( II ), both containing the bicyclo[2.2.2]octene ring system, are reported here [the structure of I has been reported previously: White & Goh (2014). Private Communication (refcode HOKRIK). CCDC, Cambridge, England]. The bond lengths and angles of the bicyclo[2.2.2]octene ring system are similar for both structures. The imide functional group of II features carbonyl C=O bond lengths of 1.209 (2) and 1.210 (2) Å, with C—N bond lengths of 1.393 (2) and 1.397 (2) Å. The five-membered imide ring is nearly planar, and it is positioned exo relative to the alkene bridgehead carbon atoms of the bicyclo[2.2.2]octene ring system. Non-covalent interactions present in the crystal structure of II include a number of C—H...O interactions. The extended structure of II also features C—H...O hydrogen bonds as well as C—H...π and lone pair–π interactions, which combine together to create supramolecular sheets. 

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4. Crystal structures of 2-bromo-1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)trisilane and 2-bromo-1,1,1,3,3,3-hexaisopropyl-2-(triisopropylsilyl)trisilane

   https://doi.org/10.1107/S2056989018009696  

   Gulotty, Eva M.; Staples, Richard J.; Biros, Shannon M.; Gaspar, Peter P.; Rath, Nigam P.; Winchester, William R. (August 2018, Acta Crystallographica Section E Crystallographic Communications)

   The synthesis and crystal structures of two tris(trialkylsilyl)silyl bromide compounds, C 9 H 27 BrSi 4 ( I , HypSiBr) and C 27 H 63 BrSi 4 ( II , TipSiBr), are described. Compound I was prepared in 85% yield by free-radical bromination of 1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)trisilane using bromobutane and 2,2′-azobis(2-methylpropionitrile) as a radical initiator at 333 K. The molecule possesses threefold rotational symmetry, with the central Si atom and the Br atom being located on the threefold rotation axis. The Si—Br bond distance is 2.2990 (12) Å and the Si—Si bond lengths are 2.3477 (8) Å. The Br—Si—Si bond angles are 104.83 (3)° and the Si—Si—Si bond angles are 113.69 (2)°, reflecting the steric hindrance inherent in the three trimethylsilyl groups attached to the central Si atom. Compound II was prepared in 55% yield by free-radical bromination of 1,1,1,3,3,3-hexaisopropyl-2-(triisopropylsilyl)trisilane using N -bromosuccinimide and 2,2′-azobis(2-methylpropionitrile) as a radical initiator at 353 K. Here the Si—Br bond length is 2.3185 (7) Å and the Si—Si bond lengths range from 2.443 (1) to 2.4628 (9) Å. The Br—Si—Si bond angles range from 98.44 (3) to 103.77 (3)°, indicating steric hindrance between the three triisopropylsilyl groups. 

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5. Crystal structure of N -butyl-2,3-bis(dicyclohexylamino)cyclopropeniminium chloride benzene monosolvate

   https://doi.org/10.1107/S2056989022008076  

   Muñoz Sánchez, Gaby M.; Zdilla, Michael J. (September 2022, Acta Crystallographica Section E Crystallographic Communications)

   N -Butyl-2,3-bis(dicyclohexylamino)cyclopropenimine ( 1 ) crystallizes from benzene and hexanes in the presence of HCl as a monobenzene solvate of the hydrochloride salt, [ 1 H]Cl·C 6 H 6 or C 31 H 54 N 3 + ·Cl − ·C 6 H 6 , in the P 2 1 / n space group. The protonation of 1 results in the generation of an aromatic structure based upon the delocalization of the cyclopropene double bond around the cyclopropene ring, giving three intermediate C—C bond lengths of ∼1.41 Å, and the delocalization of the imine-type C—N double bond, giving three intermediate C—N bond lengths of ∼1.32 Å. Ion–ion and ion–benzene packing interactions are described and illustrated. 

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