Stereochemical Control in Organic-Synthesis Using Silicon-Containing Compounds
About: This article is published in Chemical Reviews.The article was published on 1997-10-01. It has received 715 citations till now. The article focuses on the topics: Organic synthesis.
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TL;DR: This review provides a comprehensive summary of organocatalysis in inert C-H bond functionalization over the past two decades as well as those activated benzylic, allylic, and C- H bonds alpha to the heteroatom such as nitrogen and oxygen.
Abstract: As two coexisting and fast-growing research fields in modern synthetic chemistry, the merging of organocatalysis and C–H bond functionalization is well foreseeable, and the joint force along this line has been demonstrated to be a powerful approach in making inert C–H bond functionalization more viable, predictable, and selective. In this review, we provide a comprehensive summary of organocatalysis in inert C–H bond functionalization over the past two decades. The review is arranged by types of inert C–H bonds including alkane C–H, arene C–H, and vinyl C–H as well as those activated benzylic C–H, allylic C–H, and C–H bonds alpha to the heteroatom such as nitrogen and oxygen. In each section, the discussion is classified by the explicit organocatalytic mode involved.
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TL;DR: A review of recent advances in hydrosilylation chemistry mainly published in the last decade can be found in this article, where the utility of catalysts with high selectivity and efficiency is discussed.
Abstract: This review covers the recent advances in hydrosilylation chemistry mainly published in the last decade. Hydrosilylation of olefins is an important reaction for the production of various organosilicon compounds such as industrially important silicone products. Although the utility of platinum catalysts, Speier's and Karstedt's catalysts, has been widely recognized in this field for decades, development of more efficient, selective, and cheaper catalyst systems are still desired for more economical production of organosilicon materials having superior properties. In these contexts, much progress has been made in recent years. In the platinum catalysis systems, continuous progress has been made to further improve selectivity and activity. Several non-precious metal catalysts, such as Fe and Ni catalysts, with good efficiency and selectivity have been developed. Furthermore, unique chemo- and regioselectivity have been achieved not only by precious metal catalysts but also by non-precious metal catalysts. The utility of non-transition metal catalysts including early main group metals, Lewis acidic alane, borane and phosphonium salts as well as N-heterocyclic carbenes has also been disclosed.
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TL;DR: The evolution of stereoselective Lewis-acid-mediated aldol-type addition up to the recent development of chiral Lewis acids is covered, which gives the main advantages in the Mukaiyama approach are the chemoselectivity of the reaction and the possibility of stereOSElective execution.
Abstract: The aldol addition is one of the most important methods for stereoselective construction of carboncarbon bonds. New and powerful variants of these classical reactions have been developed in recent years.1 Two classes were mainly used for asymmetric induction in these reactions: the use of asymmetric modified enolates or electrophiles2 and the use of chiral Lewis acids.3 The chiral enolate or electrophile approach is much more general and gives high stereoselectivities due to the highly ordered nature of transition structures (“closed” transition models). The chiral center has to be removed after the completed aldol addition. To avoid this additional reaction step, a stategy is employed whereby achiral enolates can be reacted with achiral carbonyl compounds in the presence of additional chiral auxiliaries. This method requires the careful use of a chiral auxiliary.4 Unfortunately, however, stoichiometric amounts of the chiral information are necessary. Up to now and apart from enzymatic transformations, the so-called Mukaiyama reaction has opened an enantioselective and catalytic approach using chiral Lewis acids. This review covers the evolution of stereoselective Lewis-acid-mediated aldol-type addition up to the recent development of chiral Lewis acids. Mukaiyama et al. found that silyl enol ether reacts with carbonyl compounds in the presence of Lewis acids to give aldol products (for initial studies, see ref 5). The main advantages in the Mukaiyama approach are the chemoselectivity of the reaction and the possibility of stereoselective execution. Since the mid-1970s, the Mukaiyama reaction has become a useful method for chemoand regioselective carboncarbon bond formation.6 About 10 years later, investigations into stereochemical aspects of these reactions were initiated,7 and at the end of the 1980s, the development of chiral Lewis acids and thus the development of catalytic, enantioselective versions of the Mukaiyama reaction started.8 The reaction mechanism has not been explained yet. The most important fact is that Lewis acid enolates are not involved in this reaction.7 No transmetalation occurs. In this reaction, the Lewis acids coordinate with the carbonyl function leading to its activation.9 Two works published by Carreira and Shibasaki suggest the involvement of chiral metal enolates during the aldol addition (for copper enolates, see ref 10; for palladium enolates, see ref 11). Moreover, there is a marked stereochemical differRainer Mahrwald obtained his M.S. degree in chemistry from the MartinLuther-University, Halle, in 1973. In 1975 he joined the Institute “Manfred von Ardenne”, Dresden, where he obtained his Ph.D. in 1979 in the field of the synthesis of nuclesides. In 1980 he joined the Academy of Sciences in Berlin. There he worked in the field of total synthesis of prostaglandins. He pursued his formation as a postdoctoral fellow at Philipps-University, Marburg, in the group of Prof. M. T. Reetz (1991). Since 1994 he has been a lecturer at the Humbold-University. His main research interests have been associated with the development of catalytic stereoselective C−C bond formation. 1095 Chem. Rev. 1999, 99, 1095−1120
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TL;DR: In this article, the authors present a model for controlling dyadic add-ion reactions to double-branched double-bond reactions, including the following: 1.3-Strain Control of Dlastereoselective Intermolecular Addhion Reactions InvoMng Heteroallyl Systems 10.5.
Abstract: 5. Stereoselective Intermolecular Addhion Reactions to Double Bonds Controlled by Allylic 1,bStrain 5.1. Hydrogenation 5.2. Hydroboration 5.3. Epoxldation and Cycbpropanation 8. Diastereoselecthre Enolate Alkylations Controlled by Allyllc 1.3-Strain 7. Chirality Transfer in Reactions of Allylsilanes and Allylboronates 8. Nucleophilic AddRion to Double Bonds Controlled by Allylic 1.3-Strain 9. Reactions of Benzylic Systems Controlled by Allylic 1,3-Strain 10. Allylic 1 ,bStrain Control of Dlastereoselecthre Reactions InvoMng Heteroallyl Systems 10.1. 2-Azaallyl Systems 10.2. 2-Oxonlaallyl Systems 10.3. Ntrones 10.4. Other Azaallyllc Systems 10.5. Vinyl Sulfoxides 11. Conformational Control around Bonds to Three-Membered Rings Related to Allylic 1.3-Strain 12. Epilogue
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TL;DR: Mukaiyama et al. as mentioned in this paper showed that with the addition of titanium tetrachloride, silyl enol ethers can react with either aldehydes or ketones forming crossed aldol products.
Abstract: Synopsis: With the addition of titanium tetrachloride, silyl enol ethers can react with either aldehydes or ketones forming crossed aldol products. The carbonyl group of the aldehyde or ketone is activated by titanium tetrachloride, allowing for nucleophilic attack by a silyl enol ether at the carbonyl carbon (a titanium chelate forms as an intermediate). This addition reaction is dependent upon the metal salt, solvent, and temperature used. Critique: The fact that various reaction conditions were studied to find optimal reaction conditions that gave the highest yield of cross-aldol addition products strengthened the findings in this paper. Mukaiyama and coworkers concluded first that titanium chloride was best for this reaction compared to boron trifluoride etherate and stannic chloride. Secondly, it was observed that methylene chloride gave cross-aldol products in good yield while no reaction was observed in both diethyl ether and THF. Finally, reaction with aldehydes is favored at -78 o C while ketone reaction is favored at room temperature. It was also interesting to see that the use of unsymmetric ketones allows for regiospecific addition reactions at the olefinic position on the silyl enol ether.
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