8.4.5. Nitromercuration Reactions 3878 9. Hydroamination of Alkenes and Alkynes under Microwave Irradiation 3878 * To whom correspondence should be addressed. Phone: +49 241 8

Hydroamination: direct addition of amines to alkenes and alkynes.

The advent of well-defined catalysts for olefin metathesis which combine high activity, durability, and excellent tolerance towards polar functional groups has revolutionized the field. The past decade has seen the rapid embrace of these reagents as tools for advanced organic and polymer chemistry and the success of this development is witnessed by a plethora of elegant applications to the synthesis of natural and nonnatural products. This review article provides an overview of these developments and intends to familiarize the reader with some very recent advances which hold the promise to expand the scope of the reaction even further. Moreover, the positive impact of metathesis on the fundamental logic of retrosynthetic planning is demonstrated by means of typical examples. Finally, it will be shown that metathesis is by no means restricted to alkenes as substrates, and some comments on metathesis reactions following unconventional mechanistic pathways will also be presented.

Olefin Metathesis and Beyond

2.2.1. Polyisocyanates 6117 2.2.2. Polysilanes 6118 2.2.3. Polyacetylenes 6120 2.3. Foldamer-Based Helical Polymers 6124 2.3.1. Click Polymerization 6126 2.3.2. Ring-Closing Reaction 6126 2.4. Other Types of Helical Polymers 6127 2.4.1. π-Conjugated Helical Polymers 6127 2.4.2. Metallosupramolecular Helical Polymers 6128 2.5. Induced Helical Polymers 6130 2.5.1. Induced Helical Polyacetylenes 6130 2.5.2. Other Induced Helical Polymers and Oligomers 6132

Helical polymers: synthesis, structures, and functions

Recent developments in the synthesis and utilization of chiral sulfoxides.

Enantioselective catalytic aziridinations and asymmetric nitrene insertions into CH bonds.

The development of methodologies for efficient asymmetric synthesis is one of the most important areas of synthetic organic chemistry.1 The syntheses of biologically relevant natural and unnatural organic molecules in optically pure form are of central interest in medicinal chemistry and related disciplines. Variations in the stereochemistry of molecular probes for a target enzyme or receptor sites very often display dramatic differences in their binding properties and biological activities. For meaningful biological studies it is important, if not mandatory, to synthesize such agents in enantiomerically pure form. Recent advances in molecular biology and modern instrumentation techniques have led to a better understanding of many complex human diseases at the molecular level. Concurrent with these remarkable achievements have come new challenges and opportunities for asymmetric synthesis. Thus, from the design of enzyme inhibitors to the synthesis of receptor agonists or antagonists and bioactive natural products, asymmetric synthesis is of fundamental significance in biology and medicine.

The advances in asymmetric synthesis have now reached the point that many organic molecules can be prepared with near complete enantioselectivity. This technology is particularly sophisticated in the generation of new stereogenic centers in the presence of existing chiral centers. A number of asymmetric catalysts or so called ‘abiological catalysts’ are approaching an efficiency and selectivity comparable to enzymes such as in the asymmetric hydrogenation of dehydroamino acids utilizing chiral bisphosphine–rhodium complexes,2 asymmetric isomerization of allylic amines with rhodium(I)–BINAP complexes,3 asymmetric epoxidation of allylic alcohols,4 asymmetric epoxidation of unfunctionalized olefins,5 asymmetric reductions with chiral oxazaborolidenes6 and asymmetric dihydroxylation reactions.7 The advantage of abiological catalysts, however, is the availability of either enantiomer of the catalyst which enables one to synthesize either enantiomer of the target molecule. Today there is enormous emphasis on the design and development of efficient chiral catalysts for enantioselective synthesis and this field has become one of the most intense areas of organic chemical research.

In recent years, C2-symmetric chiral bis(oxazoline) ligand–metal complexes have received a great deal of attention through their use in various catalytic process.1c The bis(oxazoline) ligands are structurally related to C2-symmetric semicorrins pioneered by Pfaltz and co-workers.8a–c The inception of bis(oxazoline) ligands, however, added a new dimension in terms of flexibility in ligand design, convenient synthesis and availability of ligands in both enantiomeric forms. Since the early 1990s, many impressive enantioselective carbon–carbon bond forming reactions, aziridination reactions, hydrosilylations, oxidations and reductions have been recorded using bis(oxazoline)–metal complexes. The present review is intended to focus on the recent developments of bis(oxazoline) ligand–metal catalyzed asymmetric reactions and their applications in organic synthesis. The authors do not intend to provide an exhaustive review of this area since earlier developments have been reviewed by Pfaltz8a–c and Bolm.9 Applications of mono- and tris(oxazoline) ligand–metal complex catalyzed reactions are not included in this review.

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C2-Symmetric chiral bis(oxazoline)-metal complexes in catalytic asymmetric synthesis.

Ring-closing metathesis strategy to unsaturated γ- and δ-lactones: Synthesis of hydroxyethylene isostere for protease inhibitors

Conformationally constrained bis(oxazoline) derived chiral catalyst: A highly effective enantioselective Diels-Alder reaction

Synthetic studies of antitumor macrolide laulimalide: enantioselective synthesis of the c3-c14 segment by a catalytic hetero diels-alder strategy.

Asymmetric hetero Diels-Alder reactions of Danishefsky's diene and glyoxylate esters catalyzed by bis(oxazoline)-metal complex afforded the corresponding aldol adduct which upon treatment with trifluoroacetic acid furnished the hetero Diels-Alder product in 72% enantiomeric excess and 70% isolated yield.

/pdf/asymmetric-hetero-diels-alder-reactions-of-danishefsky-s-2aioqe64a9.pdf

John Cappiello

Papers

C2-Symmetric chiral bis(oxazoline)-metal complexes in catalytic asymmetric synthesis.

Ring-closing metathesis strategy to unsaturated γ- and δ-lactones: Synthesis of hydroxyethylene isostere for protease inhibitors

Conformationally constrained bis(oxazoline) derived chiral catalyst: A highly effective enantioselective Diels-Alder reaction

Synthetic studies of antitumor macrolide laulimalide: enantioselective synthesis of the c3-c14 segment by a catalytic hetero diels-alder strategy.

Asymmetric hetero diels-alder reactions of danishefsky's diene and glyoxylate esters catalyzed by chiral bisoxazoline derived catalysts.