Furans from pentoses: Pentose‐derived furfural is a commodity chemical produced from lignocellulose. A new route to furfural from renewable carbohydrates uses chromium catalysts under mild conditions to avail a chemical mechanism distinct from the usual acid catalysis. Applicable to both xylose and xylan, this new method offers an advantageous route to biomass‐derived chemicals.

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Olefin metathesis in aqueous solvents is sought for applications in green chemistry and with the hydrophilic substrates of chemical biology, such as proteins and polysaccharides. Most demonstrations of metathesis in water, however, utilize exotic complexes. We have examined the performance of conventional catalysts in homogeneous water-organic mixtures, finding that the second-generation Hoveyda-Grubbs catalyst has extraordinary efficiency in aqueous dimethoxyethane and aqueous acetone. High (71-95%) conversions are achieved for ring-closing and cross metathesis of a variety of substrates in these solvent systems.As a highly effective means for creating carbon-carbon bonds, olefin metathesis is a privileged reaction in the armamentarium of synthetic and polymer chemists. 1 Readily available and highly active ruthenium catalysts 1-4 have popularized metathesis chemistry in organic solvents ( Figure 1). 2,3 On the other hand, metathesis in aqueous solvents largely remains the domain of catalysts designed expressly for use in water (Figure 2). 4,5,6 Despite the allure of aqueous olefin metathesis for biological applications 7 and green chemistry, 8 the synthesis of these water-soluble ligands and complexes imposes barriers to their wider use. Developing aqueous reaction conditions suitable for catalysts such as 1-4 is an alternative approach. In the initial work with well-defined catalysts in aqueous systems, Grubbs and coworkers performed ring-openingmetathesis polymerization (ROMP) with 1 in aqueous emulsions, 9 a method that allowed Kiessling and coworkers to synthesize biologically active glycopolymers. 10 For ringclosing metathesis (RCM) and cross metathesis (CM), Blechert and coworkers employed commercially-available 2 and complex 6c, a relative of commercially-available 4, in watermethanol and water-DMF mixtures. 6 Although they achieved high conversion in the ringclosure of N-tosyldiallylamine (8) in 3:1 water/methanol and 3:1 water/DMF over an extended reaction time of 12 h, these reactions were not accomplished in homogenous systems: neither the substrate nor the catalyst was dissolved completely in the aqueous phase. In most cases raines@biochem.wisc.edu. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript detailed in their report, the ruthenium complex was only sparingly soluble in the aqueous reaction mixture.Metathesis in homogeneous aqueous systems would likely be faster and more versatile than in these heterogeneous systems. An effective system for metathesis with commercially available catalysts in homogeneous aqueous media would not only make this chemistry more accessible, but also highlight the limitations of the standard catalysts in water, informing catalyst-design efforts. Yet, reports of the use of common metathesis catalysts in an aqueous context are limited. For these reasons, we chose to test the capabilities of catalysts 1-4 in homogeneous aqueous media, and we report the results of our exploration herein. First, we screened various organic solvents as co-s...

Because of the elevated and sustained risk of postoperative thromboembolism, patients with IBD, especially ulcerative colitis, might benefit from extended thromboembolism prophylaxis similar to that of patients with colon cancer. See Video Abstract at http://links.lww.com/DCR/A544.

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