Chemoselective decarboxylation of higher aliphatic esters to diesel-range alkanes over the NiCu/Al2O3 bifunctional catalyst under mild reaction conditions

Previously, reagents such as sodium borohydride – boron trifluoride were shown to be capable of reducing typical aliphatic esters and lactones to the corresponding ether derivatives. Under the same reaction conditions, a variety of benzoate esters (Ib, IIb, III, and V) were essentially unaffected. Resistance to attack was illustrated by conversion, with sodium borohydride – boron trifluoride, of 3-oxo-17β-benzoyloxy-5α-androstane (III) into 3β-hydroxy-17β-benzoyloxy-5α-androstane (IV) and of reserpine (V) into alcohol VI. With aryl–carbon–oxygen bonds of the ketone VII or alcohol IXa type, reaction with sodium borohydride– boron trifluoride was shown, in general, to cause reductive fission of the benzyl–oxygen linkage (e.g. X → XI). An exception was noted in the case of tertiary benzyl alcohols containing an available β-hydrogen (e.g. IXc). Here, dehydration to yield, for example, olefin XIIb appears to be the more favorable reaction course. The marked difference in the reactivity of sodium borohydride – boron trifluoride toward benzoyl–oxygen vs. benzyl–oxygen bonds has been demonstrated.

Download Full-text

Chemo- and Regioselective Hydroformylation of Alkenes with CO2/H2 over a Bifunctional Catalyst

10.21203/rs.3.rs-85641/v1 ◽

2020 ◽

Author(s):

Kai HUA ◽

Fang Liu ◽

Yin Wei ◽

Long Shao ◽

Chao Deng ◽

...

Keyword(s):

Value Added ◽

Building Blocks ◽

Bifunctional Catalyst ◽

Basic Site ◽

Bidentate Ligands ◽

Mechanistic Studies ◽

Reaction Conditions ◽

Fast Release ◽

Value Added Products

Abstract Combining CO2 and H2 to prepare building blocks for high-value-added products is an attractive yet challenging approach. A general and selective rhodium-catalyzed hydroformylation of alkenes using CO2/H2 as a syngas surrogate is described here. With this protocol, the desired aldehydes can be obtained in up to 97% yield and 93/7 regioselectivity under mild reaction conditions (25 bar, 80 ºC). Key-to-success is the use of bifunctional Rh/PTA catalyst (PTA: 1,3,5-triaza-7-phosphaadamantane), which facilitates both CO2 hydrogenation and hydroformylation. Notably, monodentate PTA exhibited better activity and regioselectivity than common bidentate ligands, which might be ascribed to its built-in basic site and tris-chelated mode. Mechanistic studies indicate that the transformation proceeds through cascade steps, involving free HCOOH production through CO2 hydrogenation, fast release of CO, and rhodium-catalyzed conventional hydroformylation. Moreover, the unconventional hydroformylation pathway, in which HCOOAc acts as a direct C1 source, has also been proved feasible with superior regioselectivity than that of CO pathway.

Download Full-text

Highly active metal–acid bifunctional catalyst system for hydrogenolysis of glycerol under mild reaction conditions

Catalysis Communications ◽

10.1016/j.catcom.2005.06.006 ◽

2005 ◽

Vol 6 (10) ◽

pp. 645-649 ◽

Cited By ~ 171

Author(s):

Yohei Kusunoki ◽

Tomohisa Miyazawa ◽

Kimio Kunimori ◽

Keiichi Tomishige

Keyword(s):

Catalyst System ◽

Bifunctional Catalyst ◽

Reaction Conditions ◽

Highly Active ◽

Active Metal

Download Full-text

Undecagold labeling of tRNA

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100084521 ◽

1991 ◽

Vol 49 ◽

pp. 44-45

Author(s):

James F. Hainfeld ◽

Kyra M. Alford ◽

Mathias Sprinzl ◽

Valsan Mandiyan ◽

Santa J. Tumminia ◽

...

Keyword(s):

High Resolution ◽

Transmission Electron Micrograph ◽

Anticodon Loop ◽

Electron Micrograph ◽

Reaction Conditions ◽

Scanning Transmission Electron ◽

Transmission Electron ◽

Scanning Transmission

The undecagold (Au11) cluster was used to covalently label tRNA molecules at two specific ribonucleotides, one at position 75, and one at position 32 near the anticodon loop. Two different Au11 derivatives were used, one with a monomaleimide and one with a monoiodacetamide to effect efficient reactions.The first tRNA labeled was yeast tRNAphe which had a 2-thiocytidine (s2C) enzymatically introduced at position 75. This was found to react with the iodoacetamide-Aun derivative (Fig. 1) but not the maleimide-Aun (Fig. 2). Reaction conditions were 37° for 16 hours. Addition of dimethylformamide (DMF) up to 70% made no improvement in the labeling yield. A high resolution scanning transmission electron micrograph (STEM) taken using the darkfield elastically scattered electrons is shown in Fig. 3.

Download Full-text

Dimensionally-Controlled Hydrothermal Tm3+-doped Oxidic Nanocrystals and Their Photoluminescence Properties

MRS Proceedings ◽

10.1557/proc-1247-c04-15 ◽

2010 ◽

Vol 1247 ◽

Author(s):

Rocío Calderón-Villajos ◽

Carlos Zaldo ◽

Concepción Cascales

Keyword(s):

Single Crystals ◽

Fluorescence Lifetimes ◽

Photoluminescence Properties ◽

Reaction Conditions ◽

Hydrothermal Processes ◽

Bulk Single Crystals ◽

Template Free ◽

Reaction Media

AbstractControlled reaction conditions in simple, template-free hydrothermal processes yield Tm-Lu2O3 and Tm-GdVO4 nanocrystals with well-defined specific morphologies and sizes. In both oxide families, nanocrystals prepared at pH 7 reaction media exhibit photoluminescence in ∼1.95 μm similar to bulk single crystals. For the lowest Tm3+ concentration (0.2 % mol) in GdVO4 measured 3H4 and 3F4 fluorescence lifetimes τ are very near to τrad.

Download Full-text

Urea-Catalyzed Functionalization of Unactivated C–H Bonds

10.26434/chemrxiv.11886789.v1 ◽

2020 ◽

Cited By ~ 2

Author(s):

Alex L. Bagdasarian ◽

Stasik Popov ◽

Benjamin Wigman ◽

Wenjing Wei ◽

woojin lee ◽

...

Keyword(s):

Hydrogen Bonding ◽

Organic Synthesis ◽

High Energy ◽

Acid Catalysts ◽

Potential Utility ◽

New Paradigm ◽

Lewis Acid Catalysts ◽

Reaction Conditions ◽

Highly Active ◽

Acidic Nature

Herein we report the 3,5bistrifluoromethylphenyl urea-catalyzed functionalization of unactivated C–H bonds. In this system, the urea catalyst mediates the formation of high-energy vinyl carbocations that undergo facile C–H insertion and Friedel–Crafts reactions. We introduce a new paradigm for these privileged scaffolds where the combination of hydrogen bonding motifs and strong bases affords highly active Lewis acid catalysts capable of ionizing strong C–O bonds. Despite the highly Lewis acidic nature of these catalysts that enables triflate abstraction from sp<sup>2</sup> carbons, these newly found reaction conditions allow for the formation of heterocycles and tolerate highly Lewis basic heteroaromatic substrates. This strategy showcases the potential utility of dicoordinated vinyl carbocations in organic synthesis.<br>

Download Full-text

Urea-Catalyzed Functionalization of Unactivated C–H Bonds

10.26434/chemrxiv.11886789 ◽

2020 ◽

Author(s):

Alex L. Bagdasarian ◽

Stasik Popov ◽

Benjamin Wigman ◽

Wenjing Wei ◽

woojin lee ◽

...

Keyword(s):

Hydrogen Bonding ◽

Organic Synthesis ◽

High Energy ◽

Acid Catalysts ◽

Potential Utility ◽

New Paradigm ◽

Lewis Acid Catalysts ◽

Reaction Conditions ◽

Highly Active ◽

Acidic Nature

Herein we report the 3,5bistrifluoromethylphenyl urea-catalyzed functionalization of unactivated C–H bonds. In this system, the urea catalyst mediates the formation of high-energy vinyl carbocations that undergo facile C–H insertion and Friedel–Crafts reactions. We introduce a new paradigm for these privileged scaffolds where the combination of hydrogen bonding motifs and strong bases affords highly active Lewis acid catalysts capable of ionizing strong C–O bonds. Despite the highly Lewis acidic nature of these catalysts that enables triflate abstraction from sp<sup>2</sup> carbons, these newly found reaction conditions allow for the formation of heterocycles and tolerate highly Lewis basic heteroaromatic substrates. This strategy showcases the potential utility of dicoordinated vinyl carbocations in organic synthesis.<br>

Download Full-text

Direct Cyclization of Alkenyl Thioester via Transition Metal‐hydrogen Atom Transfer/radical‐polar Crossover Mechanism

10.26434/chemrxiv.10247813.v1 ◽

2019 ◽

Author(s):

Shiori Date ◽

Kensei Hamasaki ◽

Karen Sunagawa ◽

Hiroki Koyama ◽

Chikayoshi Sebe ◽

...

Keyword(s):

Natural Products ◽

Hydrogen Atom ◽

Transition Metal ◽

Hydrogen Atom Transfer ◽

Synthetic Method ◽

Atom Transfer ◽

Reaction Conditions ◽

Hydride Hydrogen ◽

Sulfur Heterocycles ◽

One Step

<div>We report here a catalytic, Markovnikov selective, and scalable synthetic method for the synthesis of saturated sulfur heterocycles, which are found in the structures of pharmaceuticals and natural products, in one step from an alkenyl thioester. Unlike a potentially labile alkenyl thiol, an alkenyl thioester is stable and easy to prepare. The powerful Co catalysis via a cobalt hydride hydrogen atom transfer and radical-polar crossover mechanism enabled simultaneous cyclization and deprotection. The substrate scope was expanded by the extensive optimization of the reaction conditions and tuning of the thioester unit.</div>

Download Full-text