The rhodium-catalyzed 1,4-addition of boronic acids (Hiyashi-Miyaura reaction) has become one of the most efficient enantioselective carbon-carbon bond-forming reactions (see Review below). The use of α,α,β-trisubstituted alkenes is still exceedingly rare. The authors show that, by using a chiral sulfinamide/alkene hybrid ligand, chiral racemic Morita-Baylis-Hillman adducts could undergo a rhodium-catalyzed conjugate addition-kinetic resolution.
The Nazarov cyclization is an excellent reaction for preparing substituted cyclopentenones. Many methods have been developed recently to modify the types of products that can be obtained (see Review below). In the present communication, the authors utilize atypical dienyl diketone starting materials. The addition of a stoichiometric nucleophile in the presence of a Lewis acid catalyst promotes a domino conjugate addition-Nazarov cyclization to provide α-hydroxycyclopentenones in high yields and complete diastereoselectivity.
Incorporation of fluorine into molecules has many effects, such as altering solubility, conformation, and reactivity. In the preparation of simple vinyl fluorides, controlling E/Z selectivity can be remarkably difficult. The authors prepare a range of vinyl fluorides starting from monofluorovinyl tosylate building blocks. Suzuki coupling of the tosylate group gives the arylated products in good yield and stereoselectivity.
Transition-metal-mediated cycloadditions are a highly efficient family of reactions for accessing medium-sized rings. Cycloheptatriene is a common 6π component, capable of reacting with various 2π partners. Based on previous work with cobalt-mediated cycloadditions with alkynes (M. Achard, A. Tenaglia, G. Buono Org. Lett. 2005, 7, 2353), the authors present a stereoselective [6+2] cycloaddition between cycloheptatriene and allenes.
Diazo compounds are excellent precursors for the generation of reactive metal carbenoid species. The authors demonstrate that triazoles bearing an electron-withdrawing heterocycle at the 1-position can serve as carbene precursors, which can subsequently undergo highly enantioselective cyclopropanation reactions or transannulations with nitriles.
The transition-metal-catalyzed syn addition of reagents across alkynes is an excellent process to synthesize substituted alkenes with high levels of stereocontrol. In the present communication, the authors report a rhodium-catalyzed silylation of alkynes, followed by addition to isonitriles. Remarkably, both E- and Z-stereoisomers can be obtained by modifying the isocyanide.
Many complex ring systems can be accessed by enantioselective cycloisomerization reactions. The transition-metal-catalyzed 1,6-enyne isomerization is a particular well-developed cycloisomerization (see Review below). The authors have combined the asymmetric rhodium-catalyzed Alder-ene reaction with an olefin isomerization process to prepare chiral dihydrobenzofurans in a domino fashion.
Polyunsaturated substrates can often undergo a variety of different cycloaddition reactions depending on the catalyst and conditions, allowing a divergent approach to complex, stereochemically rich molecules. The authors present a novel [2+2] mode of reactivity of tethered allenenes to produce bicyclo[3.2.1]heptanes.
Cycloisomerization reactions allow complex molecules to be constructed in a manner which avoids stoichiometric waste products. The authors present a domino reaction whereby substituted enones cyclize to form cationic furans, which subsequently undergo asymmetric attack from indole nucleophiles.
Olefin cross-metathesis has found widespread use in bench-scale and process chemistry as a reliable way of forming carbon-carbon double bonds (see Review below). With few exceptions, the more thermodynamically favored E-isomers are produced. The authors demonstrate that, by utilizing a novel chelated ruthenium catalyst, selectivity for the Z-isomer can be achieved.
