Abstract
Highly selective palladium-catalyzed transformations involving organoboranes, silanes, stannanes and selenides were developed by employment of pincer-complex catalysts. A novel catalytic transformation was designed for allylation of aldehyde and imine electrophiles using allylstannanes and allylboranes. These reactions proceed under mild and neutral conditions to afford homoallyl alcohols and amines with a high level of functional group tolerance. The regio- and stereoselectivity of the transformations is very high, and promising levels of enantioselectivity could be obtained by application of chiral pincer complexes. The rest of the presented reactions involve synthesis of allylstannanes, allylboranes, allenyl stannanes/silanes and organoselenides using various dimetallic reagents. Most of the presented pincer-complex-catalyzed reactions are not amenable with traditional palladium(0) catalysis. The employed mild and neutral reaction conditions allow the isolation of stereo- and regiodefined organometallic species, which are useful building blocks in advanced organic synthesis and in natural product synthesis. The mechanistic studies have revealed some important differences between the mechanism of pincer-complex-catalyzed and palladium(0)-catalyzed processes.
1 Introduction
2 General Reactivity of Pincer-Complex Catalysts in Organometallic Chemistry
3 Electrophilic Allylic Substitution of Electrophiles
3.1 Pincer-Complex-Catalyzed Electrophilic Allylation of Aldehyde and Imine Substrates with Allylstannanes
3.2 Allylation of Sulfonimines with Trifluoro(allyl)borate Substrate
3.3 Asymmetric Allylation of Sulfonimines with Chiral Pincer-Complex Catalysts
4 Synthesis of Organometallic Compounds by Pincer-Complex-Catalyzed Transformations
4.1 Synthesis of Allylstannanes Using Pincer-Complex Catalysts
4.2 Allylic Boronation Using Tetrahydroxydiboron
4.3 Trimethyltin Substitution of Propargylic Substrates
4.4 Synthesis of Allenylsilanes from Propargyl Chlorides
4.5 Phenylselenation of Organohalides
5 Cross-Coupling of Vinyl Epoxides and Aziridines with Organoboronic Acids
6 Mechanistic Aspects of the Pincer-Complex-Catalyzed Transformations
6.1 Mechanism of the Electrophilic Allylation Reactions
6.2 Transfer of the Trimethylstannyl Group to Allyl or Propargyl Substrates
7 Conclusions
Key words
allylations - boron - catalysis - palladium - tin
