The legacy of Gilbert Newton Lewis (1875-1946) pervades the lexicon of chemical bonding and reactivity. The power of his concept of donor-acceptor bonding is evident in the eponymous foundations of electron-pair acceptors (Lewis acids) and donors (Lewis bases). Lewis recognized that acids are not restricted to those substances that contain hydrogen (Bronsted acids), and helped overthrow the "modern cult of the proton". His discovery ushered in the use of Lewis acids as reagents and catalysts for organic reactions. However, in recent years, the recognition that Lewis bases can also serve in this capacity has grown enormously. Most importantly, it has become increasingly apparent that the behavior of Lewis bases as agents for promoting chemical reactions is not merely as an electronic complement of the cognate Lewis acids: in fact Lewis bases are capable of enhancing both the electrophilic and nucleophilic character of molecules to which they are bound. This diversity of behavior leads to a remarkable versatility for the catalysis of reactions by Lewis bases.

Lewis Base Catalysis in Organic Synthesis

Laboratory for Advanced Materials and New Catalysis, School of Chemistry and Materials Science, Hubei University, Wuhan 430062, China,Laboratory of Natural Gas Utilization and Applied Catalysis, Dalian Institute of Chemical Physics of Chinese Academy of Sciences, Dalian 116023,China, and Jingmen Technological College, Jingmen 448000, ChinaReceived June 30, 2004

Advances in Homogeneous and Heterogeneous Catalytic Asymmetric Epoxidation

Synthetic Methods for Compounds Having CF3–S Units on Carbon by Trifluoromethylation, Trifluoromethylthiolation, Triflylation, and Related Reactions

Stereochemical Control in Organic-Synthesis Using Silicon-Containing Compounds

The use of chiral nonracemic onium salts and crown ethers as effective phase-transfer catalysts have been studied intensively primarily for enantioselective carbon-carbon or carbon-heteroatom bond-forming reactions under mild biphasic conditions. An essential issue for optimal asymmetric catalysis is the rational design of catalysts for targeted reaction, which allows generation of a well-defined chiral ion pair that reacts with electrophiles in a highly efficient and stereoselective manner. This concept, together with the synthetic versatility of phase-transfer catalysis, provides a reliable and general strategy for the practical asymmetric synthesis of highly valuable organic compounds.

Recent advances in asymmetric phase-transfer catalysis.

New methods and reagents in organic synthesis. 75. asymmetric synthesis of α-hydroxy ketones using chiral phase transfer catalysts

Chiral quarternary ammonium fluoride. A new reagent for catalytic asymmetric aldol reactions

Oxidation of benzylic and allylic alcohols with chemical manganese dioxide smoothly proceeded under mild reaction conditions to give the corresponding aldehydes and ketones, respectively, in high yields. It is well-known that activated manganese dioxide (MnO2) is a useful reagent both for selective oxidation of benzylic and allylic alcohols to aldehydes and ketones, respectively, and for dehydrogenation of heterocycles to heteroaromatics. 1 Although several methods for preparation of activated MnO2 have been reported, 2 preparations are very tedious and sometimes the oxidation efficiency lacks reproducibility. Commercially available activated MnO 2 can also be used, but again its activity varies widely. We have already reported that chemical manganese dioxide (CMD), 3 produced for dry battery manufacture, can be efficiently used for oxidation of some allylic alcohols 4 and for dehydrogenation of heterocycles such as thiazolines, 5 2,3- dihydrofurans, 6 3-pyrrolines, 7 and 2-pyrrolines. 8 Further investigations along this line have revealed that CMD is widely applicable to the selective oxidation of benzylic and allylic alcohols 1 to aldehydes and ketones 2, respectively, as shown in Scheme 1.

http://www.sciencemadness.org/talk/files.php?pid=34476&aid=502

Chemical Manganese Dioxide (CMD), an Efficient Activated Manganese Dioxide. Application to Oxidation of Benzylic and Allylic Alcohols

Enantioselective synthesis of β-hydroxy-α-methyl carbonyl compounds by aldol reaction

Reaction conditions for the enantioselective aldol reaction of 2, 2-dimethyl-3-pentanone (3) and benzaldehyde using the chiral lithium amide 1b as a chiral auxiliary were thoroughly investigated. All three procedures, that is, (1) the combined use of lithium diisopropylamide and the chiral lithium amide 1b, (2) the use of an excess of the chiral lithium amide 1b, and (3) the regeneration of the chiral lithium amide 1b, afforded the aldol 4 in about 90% yield and 70% enantiomeric excess (ee). Investigation of the effects of solvent by utilizing 1-naphthaldehyde revealed that in tetrahydrofuran, (S, S)-aldol 5 of 77% ee was obtained as the major product, while in ether (R, R)-5 became the major isomer (38% ee). Furthermore, addition of hexamethylphosphoric triamide caused a dramatic change of stereoselectivity, and (S, S)-5 of 70% ee was obtained in ether with 20 eq of hexamethylphosphoric triamid. The aldol 4 of 74% ee was obtained when the new chiral lithium amide 6b was used.

A. Ando

Papers

New methods and reagents in organic synthesis. 75. asymmetric synthesis of α-hydroxy ketones using chiral phase transfer catalysts

Chiral quarternary ammonium fluoride. A new reagent for catalytic asymmetric aldol reactions

Chemical Manganese Dioxide (CMD), an Efficient Activated Manganese Dioxide. Application to Oxidation of Benzylic and Allylic Alcohols

Enantioselective synthesis of β-hydroxy-α-methyl carbonyl compounds by aldol reaction

Studies on Reaction Conditions and New Entry to Chiral Ligands in the Chiral Lithium Amide-Mediated Enantioselective Aldol Reaction