Alcohols can be temporarily converted into carbonyl compounds by the metal-catalysed removal of hydrogen. The carbonyl compounds are reactive in a wider range of transformations than the precursor alcohols and can react in situ to give imines, alkenes, and α-functionalised carbonyl compounds. The metal catalyst, which had borrowed the hydrogen, then returns it to the transformed carbonyl compound, leading to an overall process in which alcohols can be converted into amines, compounds containing CC bonds and β-functionalised alcohols.

Borrowing hydrogen in the activation of alcohols

Sequencing Reactions with Samarium(II) Iodide.

Microwave assisted synthesis – a critical technology overview

Polymer-Supported Organic Catalysts†

Catalytic asymmetric C-C bond-forming reactions using organometallic reagents are among the most important of organic transformations. Frequently, these transformations are key steps in the synthesis of complex biologically active molecules. The conjugate addition (CA) and allylic alkylation (AA) with organometallic compounds are especially versatile in asymmetric C-C bond-forming reactions. These transformations are complementary to the catalytic asymmetric allylic alkylation and the Michael addition, both based on soft carbon nucleophiles (Scheme 1A). For both CA and AA, the organic moiety of the organometallic reagent reacts with the sp carbon of an electron-deficient substrate, converting it to an sp carbon (Scheme 1B). In the case of CA, subsequent quenching of the enolate leads to the final product, whereas for the related AA an appropriate leaving group is expelled to form the chiral product. The organometallic compounds used most frequently for these transformations are organozinc, Grignard, organoaluminium, organolithium and cuprate reagents. Over the last three decades considerable effort has been directed toward the development of efficient catalytic systems for the asymmetric CA and AA reactions using organometallic reagents. Complexes derived from Cu salts and chiral ligands have provided the broadest scope in the catalyzed enantioselective CA and AA of organometallic reagents. Organozinc reagents have been the most successful of the organometallic reagents in this respect. Major contributions and progress in the field of asymmetric CA and AA based on organozinc reagents have been summarized in several reviews. Organomagnesium compounds were among the first organometallic compounds to be applied to synthetic organic chemistry and the use of Grignard reagents in Cu-catalyzed CA was first reported in 1941 by Kharash and Tawney. Achieving chemo-, regioand stereocontrol in both asymmetric conjugate addition (ACA) and asymmetric allylic alkylation (AAA), however, has proven to be challenging and has restricted the application of these transformations, in particular, to total synthesis. Typical selectivity issues pertain to 1,2versus 1,4-addition (Scheme 2A) and SN2versus SN2′-substitution (Scheme 2B). The challenge faced in the development of stereoselective C-C bond-forming reactions is apparent when one considers that, despite three decades of intensive research in this area, only recently has efficient Cu-catalyzed enantioselective CA of Grignard reagents been achieved. The earlier discovery of the highly enantioselective Cu-catalyzed CA of dialkylzinc reagents allowed for replacement of Grignard reagents in this asymmetric C-C bond-forming reaction. Dialkylzinc reagents offer distinct advantages over Grignard reagents in their low reactivity in noncatalyzed reactions and their high tolerance to functional groups both on the substrate and on the organozinc reagent itself. Nevertheless, there are several advantages to the use of common mono-alkylMg halide reagents, most importantly their widespread availability and the ability to transfer all of the alkyl groups of the organometallic compound. The synthetic potential of these asymmetric transformations has driven intensive research in this area, and over the past few years major breakthroughs have been realized in the enantioselective CA and AA of Grignard reagents. * Author for correspondence. E-mail: B.L.Feringa@rug.nl Chem. Rev. 2008, 108, 2824–2852 2824

Catalytic asymmetric conjugate addition and allylic alkylation with Grignard reagents.

The mechanistic study and synthetic applications of the base treatment in the ozonolytic reactions

Acetonyltriphenylphosphonium bromide and its polymer-supported analogues as catalysts in protection and deprotection of alcohols as alkyl vinyl ethers

Dibromomethane as one-carbon source in organic synthesis: microwave-accelerated α-methylenation of ketones with dibromomethane and diethylamine

Dibromomethane as one-carbon source in organic synthesis: a versatile methodology to prepare the cyclic and acyclic α-methylene or α-keto acid derivatives from the corresponding terminal alkenes

A Convenient and Efficient Workup of Ozonolysis Reactions Using Triethylamine

Yung-Son Hon

Papers

The mechanistic study and synthetic applications of the base treatment in the ozonolytic reactions

Acetonyltriphenylphosphonium bromide and its polymer-supported analogues as catalysts in protection and deprotection of alcohols as alkyl vinyl ethers

Dibromomethane as one-carbon source in organic synthesis: microwave-accelerated α-methylenation of ketones with dibromomethane and diethylamine

Dibromomethane as one-carbon source in organic synthesis: a versatile methodology to prepare the cyclic and acyclic α-methylene or α-keto acid derivatives from the corresponding terminal alkenes

A Convenient and Efficient Workup of Ozonolysis Reactions Using Triethylamine