Bio-Derived Furanic Compounds with Natural Metabolism: New Sustainable Possibilities for Selective Organic Synthesis

Biomass-derived C6-furanic compounds have become the cornerstone of sustainable technologies. The key feature of this field of chemistry is the involvement of the natural process only in the first step, i.e., the production of biomass by photosynthesis. Biomass-to-HMF (5-hydroxymethylfurfural) conversion and further transformations are carried out externally with the involvement of processes with poor environmental factors (E-factors) and the generation of chemical wastes. Due to widespread interest, the chemical conversion of biomass to furanic platform chemicals and related transformations are thoroughly studied and well-reviewed in the current literature. In contrast, a novel opportunity is based on an alternative approach to consider the synthesis of C6-furanics inside living cells using natural metabolism, as well as further transformations to a variety of functionalized products. In the present article, we review naturally occurring substances containing C6-furanic cores and focus on the diversity of C6-furanic derivatives, occurrence, properties and synthesis. From the practical point of view, organic synthesis involving natural metabolism is advantageous in terms of sustainability (sunlight-driven as the only energy source) and green nature (no eco-persisted chemical wastes)

CF ₃-Ph reductive elimination from [(Xantphos)Pd(CF ₃)(Ph)]

CF 3-Ph reductive elimination from [(Xantphos)Pd(Ph)(CF 3)] (1) and [(i-Pr-Xantphos)Pd(Ph)(CF 3)] (2) has been studied by experimental and computational methods. Complex 1 is cis in the solid state and predominantly cis in solution, undergoing degenerate cis-cis isomerization (ΔG * exp = 13.4 kcal mol -1; ΔG * calc = 12.8 kcal mol -1 in toluene) and slower cis-trans isomerization (ΔG calc = +0.9 kcal mol -1; ΔG * calc = 21.9 kcal mol -1). In contrast, 2 is only trans in both solution and the solid state with trans-2 computed to be 10.2 kcal mol -1 lower in energy than cis-2. Kinetic and computational studies of the previously communicated (J. Am. Chem. Soc. 2006, 128, 12644), remarkably facile CF 3-Ph reductive elimination from 1 suggest that the process does not require P-Pd bond dissociation but rather occurs directly from cis-1. The experimentally determined activation parameters (ΔH * = 25.9 ± 2.6 kcal mol -1; ΔS * = 6.4 ± 7.8 e.u.) are in excellent agreement with the computed data (ΔH * calc = 24.8 kcal mol -1; ΔG * calc = 25.0 kcal mol -1). ΔG * calc for CF 3-Ph reductive elimination from cis-2 is only 24.0 kcal mol -1; however, the overall barrier relative to trans-2 is much higher (ΔG * calc = 34.2 kcal mol -1) due to the need to include the energetic cost of trans-cis isomerization. This is consistent with the higher thermal stability of 2 that decomposes to PhCF 3 only at 100 °C and even then only in a sluggish and less selective manner. The presence of excess Xantphos has a minor decelerating effect on the decomposition of 1. A steady slight decrease in k obs in the presence of 1 and 2 equiv of Xantphos then plateaus at [Xantphos]:1 = 5, 10, and 20. Specific molecular interactions between 1 and Xantphos are not involved in this kinetic effect (NMR, T 1 measurements). A deduced kinetic scheme accounting for the influence of extra Xantphos involves the formation of cis-[(η 1- Xantphos) 2Pd(Ph)(CF 3)] that, by computation, is predicted to access reductive elimination of CF 3-Ph with ΔG * calc = 22.8 kcal mol -1.</p

CF3-Ph reductive elimination from [(Xantphos)Pd(CF3)(Ph)]

CF 3-Ph reductive elimination from [(Xantphos)Pd(Ph)(CF 3)] (1) and [(i-Pr-Xantphos)Pd(Ph)(CF 3)] (2) has been studied by experimental and computational methods. Complex 1 is cis in the solid state and predominantly cis in solution, undergoing degenerate cis-cis isomerization (ΔG * exp = 13.4 kcal mol -1; ΔG * calc = 12.8 kcal mol -1 in toluene) and slower cis-trans isomerization (ΔG calc = +0.9 kcal mol -1; ΔG * calc = 21.9 kcal mol -1). In contrast, 2 is only trans in both solution and the solid state with trans-2 computed to be 10.2 kcal mol -1 lower in energy than cis-2. Kinetic and computational studies of the previously communicated (J. Am. Chem. Soc. 2006, 128, 12644), remarkably facile CF 3-Ph reductive elimination from 1 suggest that the process does not require P-Pd bond dissociation but rather occurs directly from cis-1. The experimentally determined activation parameters (ΔH * = 25.9 ± 2.6 kcal mol -1; ΔS * = 6.4 ± 7.8 e.u.) are in excellent agreement with the computed data (ΔH * calc = 24.8 kcal mol -1; ΔG * calc = 25.0 kcal mol -1). ΔG * calc for CF 3-Ph reductive elimination from cis-2 is only 24.0 kcal mol -1; however, the overall barrier relative to trans-2 is much higher (ΔG * calc = 34.2 kcal mol -1) due to the need to include the energetic cost of trans-cis isomerization. This is consistent with the higher thermal stability of 2 that decomposes to PhCF 3 only at 100 °C and even then only in a sluggish and less selective manner. The presence of excess Xantphos has a minor decelerating effect on the decomposition of 1. A steady slight decrease in k obs in the presence of 1 and 2 equiv of Xantphos then plateaus at [Xantphos]:1 = 5, 10, and 20. Specific molecular interactions between 1 and Xantphos are not involved in this kinetic effect (NMR, T 1 measurements). A deduced kinetic scheme accounting for the influence of extra Xantphos involves the formation of cis-[(η 1- Xantphos) 2Pd(Ph)(CF 3)] that, by computation, is predicted to access reductive elimination of CF 3-Ph with ΔG * calc = 22.8 kcal mol -1.</p

Design of a Bimetallic Au/Ag System for Dechlorination of Organochlorides: Experimental and Theoretical Evidence for the Role of the Cluster Effect

The experimental study of dechlorination activity of a Au/Ag bimetallic system has shown formation of a variety of chlorinated bimetallic Au/Ag clusters with well-defined Au:Ag ratios from 1:1 to 4:1. It is the formation of the Au/Ag cluster species that mediated C–Cl bond breakage, since neither Au nor Ag species alone exhibited a comparable activity. The nature of the products and the mechanism of dechlorination were investigated by ESI-MS, GC-MS, NMR, and quantum chemical calculations at the M06/6-311G­(d)&SDD level of theory. It was revealed that formation of bimetallic clusters facilitated dechlorination activity due to the thermodynamic factor: C–Cl bond breakage by metal clusters was thermodynamically favored and resulted in the formation of chlorinated bimetallic species. An appropriate Au:Ag ratio for an efficient hydrodechlorination process was determined in a joint experimental and theoretical study carried out in the present work. This mechanistic finding was followed by synthesis of molecular bimetallic clusters, which were successfully involved in the hydrodechlorination of CCl₄ as a low molecular weight environment pollutant and in the dechlorination of dichlorodiphenyl­trichloroethane (DDT) as an eco-toxic insecticide. High activity of the designed bimetallic system made it possible to carry out a dechlorination process under mild conditions at room temperature

CF₃–Ph Reductive Elimination from [(Xantphos)Pd(CF₃)(Ph)]

CF₃–Ph reductive elimination from [(Xantphos)­Pd­(Ph)­(CF₃)] (<b>1</b>) and [(<i>i</i>-Pr-Xantphos)­Pd­(Ph)­(CF₃)] (<b>2</b>) has been studied by experimental and computational methods. Complex <b>1</b> is cis in the solid state and predominantly cis in solution, undergoing degenerate cis–cis isomerization (Δ<i>G</i>^≠_exp = 13.4 kcal mol^–1; <i>Δ<i>G</i></i>^≠_calc = 12.8 kcal mol^–1 in toluene) and slower cis–trans isomerization (<i>Δ<i>G</i></i>_calc = +0.9 kcal mol^–1; <i>Δ<i>G</i></i>^≠_calc = 21.9 kcal mol^–1). In contrast, <b>2</b> is only trans in both solution and the solid state with <b>trans-2</b> computed to be 10.2 kcal mol^–1 lower in energy than <b>cis-2</b>. Kinetic and computational studies of the previously communicated (<i>J. Am. Chem. Soc</i>. <b>2006</b>, <i>128</i>, 12644), remarkably facile CF₃–Ph reductive elimination from <b>1</b> suggest that the process does not require P–Pd bond dissociation but rather occurs directly from <b>cis-1</b>. The experimentally determined activation parameters (Δ<i>H</i>^≠ = 25.9 ± 2.6 kcal mol^–1; <i>Δ<i>S</i></i>^≠ = 6.4 ± 7.8 e.u.) are in excellent agreement with the computed data (Δ<i>H</i>^≠_calc = 24.8 kcal mol^–1; Δ<i>G</i>^≠_calc = 25.0 kcal mol^–1). Δ<i>G</i>^≠_calc for CF₃–Ph reductive elimination from <b>cis-2</b> is only 24.0 kcal mol^–1; however, the overall barrier relative to <b>trans-2</b> is much higher (Δ<i>G</i>^≠_calc = 34.2 kcal mol^–1) due to the need to include the energetic cost of trans–cis isomerization. This is consistent with the higher thermal stability of <b>2</b> that decomposes to PhCF₃ only at 100 °C and even then only in a sluggish and less selective manner. The presence of excess Xantphos has a minor decelerating effect on the decomposition of <b>1</b>. A steady slight decrease in <i>k</i>_obs in the presence of 1 and 2 equiv of Xantphos then plateaus at [Xantphos]:<b>1</b> = 5, 10, and 20. Specific molecular interactions between <b>1</b> and Xantphos are not involved in this kinetic effect (NMR, <i>T</i>₁ measurements). A deduced kinetic scheme accounting for the influence of extra Xantphos involves the formation of <i>cis</i>-[(η¹-Xantphos)₂Pd­(Ph)­(CF₃)] that, by computation, is predicted to access reductive elimination of CF₃–Ph with Δ<i>G</i>^≠_calc = 22.8 kcal mol^–1

CF₃–Ph Reductive Elimination from [(Xantphos)Pd(CF₃)(Ph)]

CF₃–Ph reductive elimination from [(Xantphos)­Pd­(Ph)­(CF₃)] (<b>1</b>) and [(<i>i</i>-Pr-Xantphos)­Pd­(Ph)­(CF₃)] (<b>2</b>) has been studied by experimental and computational methods. Complex <b>1</b> is cis in the solid state and predominantly cis in solution, undergoing degenerate cis–cis isomerization (Δ<i>G</i>^≠_exp = 13.4 kcal mol^–1; <i>Δ<i>G</i></i>^≠_calc = 12.8 kcal mol^–1 in toluene) and slower cis–trans isomerization (<i>Δ<i>G</i></i>_calc = +0.9 kcal mol^–1; <i>Δ<i>G</i></i>^≠_calc = 21.9 kcal mol^–1). In contrast, <b>2</b> is only trans in both solution and the solid state with <b>trans-2</b> computed to be 10.2 kcal mol^–1 lower in energy than <b>cis-2</b>. Kinetic and computational studies of the previously communicated (<i>J. Am. Chem. Soc</i>. <b>2006</b>, <i>128</i>, 12644), remarkably facile CF₃–Ph reductive elimination from <b>1</b> suggest that the process does not require P–Pd bond dissociation but rather occurs directly from <b>cis-1</b>. The experimentally determined activation parameters (Δ<i>H</i>^≠ = 25.9 ± 2.6 kcal mol^–1; <i>Δ<i>S</i></i>^≠ = 6.4 ± 7.8 e.u.) are in excellent agreement with the computed data (Δ<i>H</i>^≠_calc = 24.8 kcal mol^–1; Δ<i>G</i>^≠_calc = 25.0 kcal mol^–1). Δ<i>G</i>^≠_calc for CF₃–Ph reductive elimination from <b>cis-2</b> is only 24.0 kcal mol^–1; however, the overall barrier relative to <b>trans-2</b> is much higher (Δ<i>G</i>^≠_calc = 34.2 kcal mol^–1) due to the need to include the energetic cost of trans–cis isomerization. This is consistent with the higher thermal stability of <b>2</b> that decomposes to PhCF₃ only at 100 °C and even then only in a sluggish and less selective manner. The presence of excess Xantphos has a minor decelerating effect on the decomposition of <b>1</b>. A steady slight decrease in <i>k</i>_obs in the presence of 1 and 2 equiv of Xantphos then plateaus at [Xantphos]:<b>1</b> = 5, 10, and 20. Specific molecular interactions between <b>1</b> and Xantphos are not involved in this kinetic effect (NMR, <i>T</i>₁ measurements). A deduced kinetic scheme accounting for the influence of extra Xantphos involves the formation of <i>cis</i>-[(η¹-Xantphos)₂Pd­(Ph)­(CF₃)] that, by computation, is predicted to access reductive elimination of CF₃–Ph with Δ<i>G</i>^≠_calc = 22.8 kcal mol^–1

CF₃–Ph Reductive Elimination from [(Xantphos)Pd(CF₃)(Ph)]

CF₃–Ph reductive elimination from [(Xantphos)­Pd­(Ph)­(CF₃)] (<b>1</b>) and [(<i>i</i>-Pr-Xantphos)­Pd­(Ph)­(CF₃)] (<b>2</b>) has been studied by experimental and computational methods. Complex <b>1</b> is cis in the solid state and predominantly cis in solution, undergoing degenerate cis–cis isomerization (Δ<i>G</i>^≠_exp = 13.4 kcal mol^–1; <i>Δ<i>G</i></i>^≠_calc = 12.8 kcal mol^–1 in toluene) and slower cis–trans isomerization (<i>Δ<i>G</i></i>_calc = +0.9 kcal mol^–1; <i>Δ<i>G</i></i>^≠_calc = 21.9 kcal mol^–1). In contrast, <b>2</b> is only trans in both solution and the solid state with <b>trans-2</b> computed to be 10.2 kcal mol^–1 lower in energy than <b>cis-2</b>. Kinetic and computational studies of the previously communicated (<i>J. Am. Chem. Soc</i>. <b>2006</b>, <i>128</i>, 12644), remarkably facile CF₃–Ph reductive elimination from <b>1</b> suggest that the process does not require P–Pd bond dissociation but rather occurs directly from <b>cis-1</b>. The experimentally determined activation parameters (Δ<i>H</i>^≠ = 25.9 ± 2.6 kcal mol^–1; <i>Δ<i>S</i></i>^≠ = 6.4 ± 7.8 e.u.) are in excellent agreement with the computed data (Δ<i>H</i>^≠_calc = 24.8 kcal mol^–1; Δ<i>G</i>^≠_calc = 25.0 kcal mol^–1). Δ<i>G</i>^≠_calc for CF₃–Ph reductive elimination from <b>cis-2</b> is only 24.0 kcal mol^–1; however, the overall barrier relative to <b>trans-2</b> is much higher (Δ<i>G</i>^≠_calc = 34.2 kcal mol^–1) due to the need to include the energetic cost of trans–cis isomerization. This is consistent with the higher thermal stability of <b>2</b> that decomposes to PhCF₃ only at 100 °C and even then only in a sluggish and less selective manner. The presence of excess Xantphos has a minor decelerating effect on the decomposition of <b>1</b>. A steady slight decrease in <i>k</i>_obs in the presence of 1 and 2 equiv of Xantphos then plateaus at [Xantphos]:<b>1</b> = 5, 10, and 20. Specific molecular interactions between <b>1</b> and Xantphos are not involved in this kinetic effect (NMR, <i>T</i>₁ measurements). A deduced kinetic scheme accounting for the influence of extra Xantphos involves the formation of <i>cis</i>-[(η¹-Xantphos)₂Pd­(Ph)­(CF₃)] that, by computation, is predicted to access reductive elimination of CF₃–Ph with Δ<i>G</i>^≠_calc = 22.8 kcal mol^–1