LongLarf

Going for a ′SPIN′: The enantioselective synthesis of a series of 3,3′‐diarylated 1,1′‐spirobiindane‐7,7′‐diols (3,3′‐diaryl‐SPINOLs) was developed using a sequential Rh‐catalyzed twofold asymmetric conjugate arylation/BF₃‐promoted diastereoselective spirocyclization. Some phosphoramidite ligands were prepared from the 3,3′‐Ph‐SPINOL and applied to several catalytic asymmetric reactions, and the 3,3′‐diarylated ligands showed higher enantioselectivities than the privileged nonsubstituted ligands.

Abstract

The enantioselective synthesis of a series of C₂‐symmetric 3,3′‐diarylated 1,1′‐spirobiindane‐7,7′‐diols (3,3′‐diaryl‐SPINOLs) was developed by sequential Rh‐catalyzed twofold asymmetric conjugate arylation/BF₃‐promoted diastereoselective spirocyclization (>20:1 d.r. and >99 % ee for all examples). Some phosphoramidite ligands were prepared from the 3,3′‐Ph‐SPINOL and applied to several catalytic asymmetric reactions, and the 3,3′‐diarylated ligands showed higher enantioselectivities than the privileged nonsubstituted ligands.

Publication date: 22 February 2019

Source: Tetrahedron, Volume 75, Issue 8

Author(s): Jun Xiong, Xiao Wei, Yu-Chen Wan, Ming-Wu Ding

Graphical abstract

Publication date: 1 March 2019

Source: Tetrahedron, Volume 75, Issue 9

Author(s): Yingying Wang, Yang Zhou, Min Lei, Jinjun Hou, Qinghao Jin, Dean Guo, Wanying Wu

Graphical abstract

Synlett
DOI: 10.1055/s-0037-1611699

Organophosphonate analogues are important structural motifs that are present in bioactive natural products, pharmaceuticals, and agrochemicals. Because they are useful in a broad range of applications, much effort has focused on developing efficient synthetic methods that enable access to organophosphonates and their derivatives. However, currently available synthetic procedures rely on harsh reaction conditions and are limited to a narrow substrate scope. Our lab has recently made important advances in leveraging inert phosphonates/phosphates into functional phosphorus compounds such as mixed phosphonates, phosphates, and mixed aryl phosphate derivatives. Presented herein is an overview of recent achievements in the synthesis of phosphonate/phosphate derivatives and a summary of our recent accomplishments in Tf2O-promoted activating strategy of phosphonate analogues.1 Introduction2 Direct Activating Strategy of Phosphonate Analogues3 Late-stage Phosphonylation of Natural Compounds4 Potential Applications5 Summary
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© Georg Thieme Verlag Stuttgart · New York

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Synlett
DOI: 10.1055/s-0037-1611958

Whereas two equivalents of base are typically required to prepare carboxylate (CO2 –) ylides [Ph3P+C–(H)-alk-CO2 –] (alk = alkanediyl) from carboxy (CO2H) phosphonium salts [(Ph3PCH2-alk-CO2H)+] X–, we reveal, for the first time, that carboxy ylides [Ph3P+C–(H)-alk-CO2H] can be generated with one equivalent of NaHMDS at 0 °C, and that the Wittig reaction of simple aliphatic aldehydes (1 equiv) with these carboxy ylides (1.5–2 equiv) in THF at –95 to –90 °C for one hour, then at warming temperatures to 0 °C over two hours affords (Z)-alkenoic acids. Phosphonium salts containing (CH2) n alkanediyl chains (n = 2–5) showed adequate reactivity and high Z-selectivity, whereas shorter or longer alkanediyl chains resulted in a low Z-selectivity and/or a low yield. On the basis of these results with different (CH2) n chains and that obtained with a rigid methylene group, we propose that a rapid equilibrium between Ph3PCH 2-alk-CO2 – and Ph3P+C–(H)-alk-CO2 H, through an intramolecular hydrogen exchange, accounts for the success of the Wittig reaction.
[...]

© Georg Thieme Verlag Stuttgart · New York

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Synlett
DOI: 10.1055/s-0037-1611976

Wittig reactions using carboxy (CO2H) ylides derived from a carboxylic phosphonium salt and NaN(TMS)2 (NaHMDS) in a 1:1 ratio were applied to the synthesis of 8-HEPE and 10-HDoHE, which are metabolites of eicosapentaenoic acid and docosahexaenoic acid, respectively. The attempted Wittig reaction of 3-(TBS-oxy)pentadeca-4E,6Z,9Z,12Z-tetraenal with the carboxy ylide (2 equiv) derived from Br– Ph3P+(CH2)4CO2H and NaHMDS (1:1) competed with the elimination of the TBS-oxy group at C3 to give a mixture of the Wittig product and the elimination product in 45–50% and 30–40% yields, respectively. The elimination was suppressed completely by using three equiv of the carboxy ylides in THF/HMPA (7–8:1), and the subsequent desilylation gave 8-HEPE in (R)- and (S)-forms. Similarly, both enantiomers of 10-HDoHE were synthesized.
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© Georg Thieme Verlag Stuttgart · New York

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Oat field: A method for electrophilic sulfenylation by organophosphorus‐catalyzed deoxygenative O‐atom transfer (OAT) from sulfonyl chlorides is reported. This C−S bond‐forming reaction is catalyzed by 1 (phosphetane) in conjunction with a hydrosilane terminal reductant to afford sulfenyl electrophiles, including valuable trifluoromethyl, perfluoroalkyl, and heteroaryl derivatives.

Abstract

A method for electrophilic sulfenylation by organophosphorus‐catalyzed deoxygenative O‐atom transfer from sulfonyl chlorides is reported. This C−S bond‐forming reaction is catalyzed by a readily available small‐ring phosphine (phosphetane) in conjunction with a hydrosilane terminal reductant to afford a general entry to sulfenyl electrophiles, including valuable trifluoromethyl, perfluoroalkyl, and heteroaryl derivatives that are otherwise difficult to access. Mechanistic investigations indicate that the twofold deoxygenation of the sulfonyl substrate proceeds by the intervention of an off‐cycle resting state thiophosphonium ion. The catalytic method represents an operationally simple protocol using a stable phosphine oxide as a precatalyst and exhibits broad functional‐group tolerance.

A comprehensive metabolic map for production of bio-based chemicals

A comprehensive metabolic map for production of bio-based chemicals, Published online: 14 January 2019; doi:10.1038/s41929-018-0212-4

Production of industrial chemicals from renewable biomass feedstock plays an important role in addressing limited fossil fuel resources, climate change and environmental problems. This Review provides a comprehensive overview of biological and chemical routes for the synthesis of industrial chemicals derived from key precursor metabolites of central carbon metabolic pathways, and visualizes the results in a global bio-based chemicals map.

Synlett
DOI: 10.1055/s-0037-1611958

Whereas two equivalents of base are typically required to prepare carboxylate (CO2 –) ylides [Ph3P+C–(H)-alk-CO2 –] (alk = alkanediyl) from carboxy (CO2H) phosphonium salts [(Ph3PCH2-alk-CO2H)+] X–, we reveal, for the first time, that carboxy ylides [Ph3P+C–(H)-alk-CO2H] can be generated with one equivalent of NaHMDS at 0 °C, and that the Wittig reaction of simple aliphatic aldehydes (1 equiv) with these carboxy ylides (1.5–2 equiv) in THF at –95 to –90 °C for one hour, then at warming temperatures to 0 °C over two hours affords (Z)-alkenoic acids. Phosphonium salts containing (CH2) n alkanediyl chains (n = 2–5) showed adequate reactivity and high Z-selectivity, whereas shorter or longer alkanediyl chains resulted in a low Z-selectivity and/or a low yield. On the basis of these results with different (CH2) n chains and that obtained with a rigid methylene group, we propose that a rapid equilibrium between Ph3PCH 2-alk-CO2 – and Ph3P+C–(H)-alk-CO2 H, through an intramolecular hydrogen exchange, accounts for the success of the Wittig reaction.
[...]

© Georg Thieme Verlag Stuttgart · New York

Article in Thieme eJournals:
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Long‐lived replacements: Ruthenium complexes with polypyridine ligands are very popular choices for applications in photophysics and photochemistry, but ruthenium is rare and expensive, whereas iron is comparatively abundant and cheap. Key concepts to obtain long‐lived charge‐transfer excited states in iron complexes (see figure) are discussed and recent conceptual breakthroughs are highlighted.

Abstract

Ruthenium complexes with polypyridine ligands are very popular choices for applications in photophysics and photochemistry, for example, in lighting, sensing, solar cells, and photoredox catalysis. There is a long‐standing interest in replacing ruthenium with iron because ruthenium is rare and expensive, whereas iron is comparatively abundant and cheap. However, it is very difficult to obtain iron complexes with an electronic structure similar to that of ruthenium(II) polypyridines. The latter typically have a long‐lived excited state with pronounced charge‐transfer character between the ruthenium metal and ligands. These metal‐to‐ligand charge‐transfer (MLCT) excited states can be luminescent, with typical lifetimes in the range of 100 to 1000 ns, and the electrochemical properties are drastically altered during this time. These properties make ruthenium(II) polypyridine complexes so well suited for the abovementioned applications. In iron(II) complexes, the MLCT states can be deactivated extremely rapidly (ca. 50 fs) by energetically lower lying metal‐centered excited states. Luminescence is then no longer emitted, and the MLCT lifetimes become much too short for most applications. Recently, there has been substantial progress on extending the lifetimes of MLCT states in iron(II) complexes, and the first examples of luminescent iron complexes have been reported. Interestingly, these are iron(III) complexes with a completely different electronic structure than that of commonly targeted iron(II) compounds, and this could mark the beginning of a paradigm change in research into photoactive earth‐abundant metal complexes. After outlining some of the fundamental challenges, key strategies used so far to enhance the photophysical and photochemical properties of iron complexes are discussed and recent conceptual breakthroughs are highlighted in this invited Concept article.

Siloxanes unraveled! Oligosiloxanes with polycyclic and asymmetric cage structures have been synthesized by the hydrolysis and intramolecular condensation of alkoxysilylated cyclosiloxanes (see scheme). These oligosiloxanes are attractive as nanobuilding blocks for the construction of a variety of siloxane‐based nanomaterials.

Abstract

The controlled synthesis of oligosiloxanes with well‐defined structures is important for the bottom‐up design of siloxane‐based nanomaterials. This work reports the synthesis of various polycyclic and cage siloxanes by the hydrolysis and intramolecular condensation of monocyclic tetra‐ and hexasiloxanes functionalized with various alkoxysilyl groups. An investigation of monoalkoxysilylated cyclosiloxanes revealed that intramolecular condensation occurred preferentially between adjacent alkoxysilyl groups to form new tetrasiloxane rings. The study of dialkoxy‐ and trialkoxysilylated cyclotetrasiloxanes revealed multistep intramolecular condensation reactions to form cubic octasiloxanes in relatively high yields. Unlike conventional methods starting from organosilane monomers, intramolecular condensation enables the introduction of different organic substituents in controlled arrangements. So‐called Janus cubes have been successfully obtained, that is, Ph₄R₄Si₈O₁₂, in which R=Me, OSiMe₃, and OSiMe₂Vi (Vi=vinyl). These findings will enable the creation of siloxane‐based materials with diverse functions.