Hydrogenation for C  C Bond Formation

Abstract

The formation of chemical bonds between carbon atoms is of fundamental significance. A major goal in the emerging field of green chemistry involves the design of by-product-free chemical processes, especially CÀC bond-forming processes applicable to renewable feedstocks [1]. This objective is aligned with longstanding economic and aesthetic forces that have shaped the field of chemical synthesis and which have given rise to such concepts as atom-economy [2], step-economy and the ideal synthesis [3]. As revealed by the E-factor (kilogram of waste generated per kilograms of product) [4], it is not surprising that an inverse correlation between process volume and waste generation exists in the chemical industry. For largevolume processes, where minute improvements in efficiency confer significant economic return, by-product-free chemical processes are desirable as they mitigate costs associated with waste disposal and product isolation. Here, fiscal natural selection mandates the practice of green chemistry. In contrast, the fine chemical and pharmaceutical industrial segments often engage in multi-step syntheses where the value of late-stage intermediates can easily exceed the cost of waste stream disposal or product separation, undermining motivation to develop by-product-free protocols (Table 8.1).Must waste production generally increase with increasing molecular complexity? What transformations would be practiced on a vast scale if only efficient by-productfree variants were developed? In the specific case of CÀC bond-forming processes, especially those involving non-stabilized carbanions and their equivalents, a significant cause of waste production resides in the use of stoichiometrically preformed organometallic reagents, which give rise to equimolar quantities of chemical byproducts in the form of metal salts. For example, the vinylation and allylation of carbonyl compounds and imines, which are core reactions in synthetic organic chemistry, uniformly employ preformed vinylmetal and allylmetal reagents. The Green Catalysis, Volume 1: Homogeneous Catalysis. Edited by Robert H. Crabtree

The Radio Light Curve of the Gamma-Ray Nova in V407 Cyg: Thermal Emission From the Ionized Symbiotic Envelope, Devoured From Within by the Nova Blast

“…Additional radio continuum data were published by Nestoras et al (2010), Gawronski et al (2010), Pooley (2010), and Bower et al (2010) in Astronomer's Telegrams. Unfortunately, the facilities and frequencies used for these measurements are heterogeneous, so they are difficult to integrate into our VLA light curve and are not used in our analysis (although a spectral index from the Nestoras et al data is listed in Table 2).…”

“…This paper presents complementary radio continuum observations of the 2010 outburst, obtained between 1-45 GHz with the Karl G. Jansky Very Large Array (VLA; Perley et al 2011). Before the 2010 outburst, no radio detections of V407 Cyg had ever been reported (although, see Section 7), but shortly after the nova explosion, V407 Cyg was strongly detected across the centimeter and millimeter bands (Nestoras et al 2010;Gawronski et al 2010;Pooley 2010;Bower et al 2010;Krauss et al 2010). In Section 2, we present our data and describe the radio light curve.…”

Catalytic Carbonyl Addition through Transfer Hydrogenation: A Departure from Preformed Organometallic Reagents

“…In preliminary studies, a chiral iridium complex modified by ( R )-C3-TUNEPHOS was found to promote the coupling of 1,1-dimethylallene to p -nitrobenzyl alcohol in 55% isolated yield and 76% enantiomeric excess. [17] Erosion of enantiomeric excess is not observed under the coupling conditions, indicating that the product of carbonyl allylation, a secondary alcohol, is not subject to redox equilibration.…”

E-EVN observations of the first gamma-ray nova V407 Cyg

“…A fair amount of extended emission was also present, but impossible to image or model fit reliably with the spatial frequencies available to VLBI. We note that the Allen Telescope Array measured a flux density of 5.8 ± 0.9 mJy at the same frequency just two days earlier [2], clearly indicating that the majority of the flux density at this epoch and frequency is emitted on larger angular scales.…”