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1. Formic acid catalyzed isomerization and adduct formation of an isoprene-derived Criegee intermediate: experiment and theory

   https://doi.org/10.1039/d0cp05018k  

   Vansco, Michael F. ; Caravan, Rebecca L. ; Pandit, Shubhrangshu ; Zuraski, Kristen ; Winiberg, Frank A. ; Au, Kendrew ; Bhagde, Trisha ; Trongsiriwat, Nisalak ; Walsh, Patrick J. ; Osborn, David L. ; et al ( December 2020 , Physical Chemistry Chemical Physics)

   null (Ed.)

   Isoprene is the most abundant non-methane hydrocarbon emitted into the Earth's atmosphere. Ozonolysis is an important atmospheric sink for isoprene, which generates reactive carbonyl oxide species (R 1 R 2 CO + O − ) known as Criegee intermediates. This study focuses on characterizing the catalyzed isomerization and adduct formation pathways for the reaction between formic acid and methyl vinyl ketone oxide (MVK-oxide), a four-carbon unsaturated Criegee intermediate generated from isoprene ozonolysis. syn -MVK-oxide undergoes intramolecular 1,4 H-atom transfer to form a substituted vinyl hydroperoxide intermediate, 2-hydroperoxybuta-1,3-diene (HPBD), which subsequently decomposes to hydroxyl and vinoxylic radical products. Here, we report direct observation of HPBD generated by formic acid catalyzed isomerization of MVK-oxide under thermal conditions (298 K, 10 torr) using multiplexed photoionization mass spectrometry. The acid catalyzed isomerization of MVK-oxide proceeds by a double hydrogen-bonded interaction followed by a concerted H-atom transfer via submerged barriers to produce HPBD and regenerate formic acid. The analogous isomerization pathway catalyzed with deuterated formic acid (D 2 -formic acid) enables migration of a D atom to yield partially deuterated HPBD (DPBD), which is identified by its distinct mass ( m / z 87) and photoionization threshold. In addition, bimolecular reaction of MVK-oxide with D 2 -formic acid forms a functionalized hydroperoxide adduct, which is the dominant product channel, and is compared to a previous bimolecular reaction study with normal formic acid. Complementary high-level theoretical calculations are performed to further investigate the reaction pathways and kinetics. 

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2. Ligand control in chemo, regio-and enantioselective cycloaddition of alkynes and 1,3-dienes

   Singh, D. ; Parsutkar, M. M. ; RajanBabu, T. V. ( March 2022 , Abstract of Papers, ACS Spring National Meeting, , March 20-24, 2022. Abstract: CAPlus AN: 2022:2171183)

   Asymmetric synthesis of substituted 1,4 cyclohexadienes and cyclobutenes has received great attention in recent years. Strategies such as base metal catalyzed cycloaddition bypass the need of harsh reaction conditions which are often required for synthesis of such motifs. These strategies using base-metals as catalysts are also valuable in constructing substituted cyclic motifs from readily available and inexpensive materials such as dienes and alkynes. Such reactions can be cost effective and environmentally friendly. In past decade, low valent cobalt has shown promising reactivity in forming new C-C and C-X (e. g., X= Si, B, N) bonds in high stereoselectivity. Through our studies, we found that cationic cobalt(I) complexes can catalyze intermolecular cycloaddition reactions of alkyne and 1,3-dienes in regio-and enantioselective manner. We also discovered that the involvement of 4 pi electrons or 2 pi electrons of 1,3-dienes can be controlled by the judicious choice of ligands employed on cobalt leading to [4+2] and [2+2] cycloaddition products respectively in high regio- and stereoselectivity. This excellent selectivity complimented with moderate to good yields provided us with broadly applicable protocol for synthesis of diversely substituted enantiopure cyclic motifs with enantiomeric excesses upto 99%. The scope of this method has been expanded over simple aliphatic and aromatic 1,3-dienes and alkynes bearing various functional groups. The methodical development of this transformation along with the ligand effects and possible mechanisms will be discussed in detail. 

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3. Ligand control in chemo, regio-and enantioselective cycloaddition of alkynes and 1,3-dienes

   Singh, D. ; Parsutkar, M. M. ; RajanBabu, T. V. ( March 2022 , Abstracts of papers American Chemical Society)

   Asymmetric synthesis of substituted 1,4 cyclohexadienes and cyclobutenes has received great attention in recent years. Strategies such as base metal catalyzed cycloaddition bypass the need of harsh reaction conditions which are often required for synthesis of such motifs. These strategies using base-metals as catalysts are also valuable in constructing substituted cyclic motifs from readily available and inexpensive materials such as dienes and alkynes. Such reactions can be cost effective and environmentally friendly. In past decade, low valent cobalt has shown promising reactivity in forming new C-C and C-X (e. g., X= Si, B, N) bonds in high stereoselectivity. Through our studies, we found that cationic cobalt(I) complexes can catalyze intermolecular cycloaddition reactions of alkyne and 1,3-dienes in regio-and enantioselective manner. We also discovered that the involvement of 4-pi electrons or 2-pi electrons of 1,3-dienes can be controlled by the judicious choice of ligands employed on cobalt leading to [4+2] and [2+2] cycloaddition products respectively in high regio- and stereoselectivity. This excellent selectivity complimented with moderate to good yields provided us with broadly applicable protocol for synthesis of diversely substituted enantiopure cyclic motifs with enantiomeric excesses upto 99%. The scope of this method has been expanded over simple aliphatic and aromatic 1,3-dienes and alkynes bearing various functional groups. The methodical development of this transformation along with the ligand effects and possible mechanisms will be discussed in detail. 

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4. Alkylation of poly-substituted aromatics to probe effects of mesopores in hierarchical zeolites with differing frameworks and crystal sizes

   https://doi.org/10.1039/D1ME00062D  

   Adawi, Hayat I. ; Odigie, Florence O. ; Sarazen, Michele L. ( November 2021 , Molecular Systems Design & Engineering)

   This study examines how the inherent diffusion constraints of MFI (3D, pore-limiting diameter (PLD) = 0.45 nm), BEA (3D, PLD = 0.60 nm), and MOR (1D, PLD = 0.65 nm) zeolite architectures, at both nanocrystal (nMFI, nBEA, nMOR; d crystal < 0.5 μm) and microcrystal (μBEA, μMOR; d crystal > 0.5 μm) scales, impact functions of mesopores in their hierarchical analogs. Reactivities, deactivation rates, and product selectivities were compared among zeolites, as well as to a mesoporous aluminosilicate control (Al-MCM-41; PLD = 6.2 nm), during Friedel–Crafts alkylation of 1,3,5-trimethylbenzene (TMB; d vdW = 0.72 nm) with benzyl alcohol (BA; d vdW = 0.58 nm) to form 1,3,5-trimethyl-2-benzylbenzene (TM2B; d vdW = 0.75 nm). Operation in the neat liquid phase ([TMB] 0  : [BA] 0 = 35 : 1, 393 K) ensured that the parallel BA self-etherification to yield dibenzyl ether (DBE; d vdW = 0.58 nm) occurred only at the expense of TM2B production when the alkylation reaction was impeded due to hindered access of TMB to confined protons. Investigation of secondary TM2B formation from reaction of DBE with TMB at low [BA]/[DBE] indicates an additional route of selectivity control for hierarchical zeolites that can achieve high BA conversion ( X BA > 0.9) with no DBE cofeed. These findings highlight a compounding advantage of increased diffusivity in mesopores that alter rates, extend lifetimes, and subsequently permit secondary reactions that enable significant shifts in product distribution. Fundamental insights into hierarchical zeolite reaction–diffusion–deactivation for alkylation of poly-substituted aromatics, as detailed here, can be applied broadly to reactions of other bulky species, including biomass-derived oxygenates, for more atom-efficient chemical and fuel production. 

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5. Three-step cascade over a single catalyst: synthesis of 5-(ethoxymethyl)furfural from glucose over a hierarchical lamellar multi-functional zeolite catalyst

   https://doi.org/10.1039/C8TA01242C  

   Bai, Yuanyuan ; Wei, Lu ; Yang, Mengfei ; Chen, Huiyong ; Holdren, Scott ; Zhu, Guanghui ; Tran, Dat T. ; Yao, Chunli ; Sun, Runcang ; Pan, Yanbo ; et al ( January 2018 , Journal of Materials Chemistry A)

   The synthesis of hierarchical lamellar zeolites with a controlled meso-/microporous morphology and acidity is an expanding area of research interest for a wide range of applications. Here, we report a one-step synthesis of a hierarchical meso-/microporous lamellar MFI–Sn/Al zeolite ( i.e. , containing both Lewis acidic Sn- and Al-sites and a Brønsted acidic Al–O(H)–Si site) and its catalytic application for the conversion of glucose into 5-(ethoxymethyl)furfural (EMF). The MFI–Sn/Al zeolite was prepared with the assistance of a diquaternary ammonium ([C 22 H 45 –N + (CH 3 ) 2 –C 6 H 12 –N + (CH 3 ) 2 –C 6 H 13 ]Br 2− , C 22-6-6 ) template in a composition of 100SiO 2 /5C 22-6-6 /18.5Na 2 O/ x Al 2 O 3 / y SnO 2 /2957H 2 O ( x = 0.5, 1, and 2; y = 1 and 2, respectively). The MFI–Sn/Al zeolites innovatively feature dual meso-/microporosity and dual Lewis and Brønsted acidity, which enabled a three-step reaction cascade for EMF synthesis from glucose in ethanol solvent. The reaction proceeded via the isomerization of glucose to fructose over Lewis acidic Sn sites and the dehydration of fructose to 5-hydroxymethylfurfural (HMF) and then the etherification of HMF and ethanol to EMF over the Brønsted acidic Al–O(H)–Si sites. The co-existence of multiple acidities in a single zeolite catalyst enabled one-pot cascade reactions for carbohydrate upgrading. The dual meso-/microporosity in the MFI–Sn/Al zeolites facilitated mass transport in processing of bulky biomass molecules. The balance of both types of acidity and meso-/microporosity realized an EMF yield as high as 44% from the glucose reactant. 

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