Direct Catalytic Asymmetric Aldol Reaction:  Synthesis of Either syn- or anti-α,β-Dihydroxy Ketones  [J. Am. Chem. Soc. 2001, 123, 2466−2467].

Abstract

As the title states, this book describes the chemistry of inhibitors, chemical species that reduce the rate of certain chemical reactions or that prevent or delay the oxidative decomposition of organic compounds and materials. In the latter case, the "inhibitor" is more commonly referred to as an antioxidant. In the instances discussed, the mechanism of inhibition involves intercepting a reactive free radical intermediate, and thus, the text also provides an overview of free radical chain processes.The text has three parts. The first deals with "straight chain reactions", characterized by elementary steps that consume and produce a reactive free radical (propagation steps) to sustain the chain process. This section discusses the general kinetic characteristics of such processes, including the effect of inhibitors on rate, and treats a number of important topics, including free radical polymerization and the oxidation of hydrocarbons. In addition, important classes of inhibitors (antioxidants), such as phenols and aromatic amines, are discussed separately in considerable detail. The second part of the book covers degenerate chain branching reactions. These are reactions in which the initially formed products provide new pathways for the production of free radicals. This section deals mostly with autoxidation of organic compounds and materials and the chemistry of hydroperoxides (ROOH) and peroxyl radicals (ROO • ). The last section of the book deals with branching chain processes, which are characterized by elementary steps that generate more radicals than they consume. Accordingly, this section considers the effect of inhibitors on ignition, combustion, and explosion.The reactions are discussed in terms of their kinetics and, to a somewhat lesser extent, their thermodynamics. Many of the reactions of inhibitors with radicals involve atom transfer, typically hydrogen atom transfer. There is an excellent presentation and application of a theory that expresses the activation energy as a function of the bond strengths of the pertinent chemical species, triplet repulsion in the transition state, etc., enabling the reader to achieve a good appreciation of the factors that govern the rate of these reactions. The text, however, does not go into great detail describing the molecular basis for radical reactivity, structural effects, applications of MO theory, etc. and should not be viewed as a comprehensive treatise on free radical chemistry. To get the most out of the text, the reader will need to be fairly comfortable with chemical kinetics, as most of the reaction mechanisms are discussed in terms of moderately complicated rate equations.The book is translated from Russian but does not read like a translation, in that the text flows smoothly and is free of grammatical errors. The material is certainly up-to-date, but most of the references predate 1990, partly reflecting the maturity of the field. There are some modern topics discussed, including the effect of hydrogen bonding on the reactivity of phenols as radical tr...

Enantioselective ProPhenol-Catalyzed Addition of 1,3-Diynes to Aldehydes to Generate Synthetically Versatile Building Blocks and Diyne Natural Products

“…Although ethyl acetate and ethylene carbonate gave only modest improvements in the selectivity of the diyne addition (entries 4 and 5, respectively), they proved that a catalytic additive could enhance the reaction. The Trost10a,11 and Shibasaki12 groups previously demonstrated that oxidized phosphines could significantly impact both the reactivity and diastereoselectivity, respectively, of dinuclear zinc-catalyzed aldol reactions. Moreover, Shibasaki and coworkers have repeatedly exploited this phenomenon for 1,2-additions of various nucleophiles to aldehydes with polymetallic catalysts 13.…”

“Designer Acids”: Combined Acid Catalysis for Asymmetric Synthesis

“…The LLB catalyst also works well for the direct aldol reaction of aldehydes with a-hydroxy ketones to provide 1,2-dihydroxyketones with high enantiomeric excess. [29] A practical and efficient Michael addition for the largescale synthesis of enantiomerically pure (R)-3-[bis(methoxycarbonyl)methyl]cyclohexanones in the presence of an (R)-Al-Li-bis(binaphthoxide) complex ((R)-ALB) [30] was developed (Scheme 21). [31] The Michael reaction of 2-cyclohexeScheme 19.…”

Hoch effiziente asymmetrische Katalyse durch doppelte Aktivierung von Nucleophil und Elektrophil

“…Carreira et al demonstrierten die Nützlichkeit chiraler Kom- [64] 33 bewährt sich auch bei der direkten Aldolreaktion von Aldehyden mit a-Hydroxyketonen und liefert 1,2-Dihydroxyketone mit hohen Enantiomerenüberschüssen. [65] Der chirale Et 2 Zn/35-Komplex mit einem 3--Molekularsieb fördert schon bei 0.1 Mol-% von 35 und 0.4 Mol-% Et 2 Zn effizient direkte Aldolreaktionen und führt zu Diolen in guten Ausbeuten (bis zu 97 %) mit hohen Stereoselektivitäten (bis zu 98:2 d.r. und 97 % ee).…”