Vinyl boronic esters are valuable substrates for Suzuki-Miyaura cross-coupling reactions. However, boron-substituted alkenes have drawn little attention as radical acceptors, and the radical chemistry of vinylboron ate complexes is underexplored. We show here that carbon radicals add efficiently to vinylboron ate complexes and that their adduct radical anions undergo radical-polar crossover: A 1,2-alkyl/aryl shift from boron to the α-carbon sp center provides secondary or tertiary alkyl boronic esters. In contrast to the Suzuki-Miyaura coupling, a transition metal is not required, and two carbon-carbon bonds are formed. The valuable boronic ester moiety remains in the product and can be used in follow-up chemistry, enlarging the chemical space of the method. The cascade uses commercial starting materials and provides access to perfluoroalkylated alcohols, γ-lactones, γ-hydroxy alkylnitriles, and compounds bearing quaternary carbon centers.

Asymmetric synthesis of diarylmethylamines with high enantioselectivity (95-99% ee) was realized by use of a new C2-symmetric diene ligand, (1R,4R)-2,5-diphenylbicyclo[2.2.2]octa-2,5-diene (Ph-bod*), for the rhodium-catalyzed asymmetric arylation of N-tosylarylimines with arylboroxines.

Rhodium-catalyzed asymmetric arylation of imines using electronically and sterically-modified chiral diene ligands gave the corresponding diarylmethylamines in high yield and with high enantioselectivity using just 0.3 mol% of catalyst.

[reaction: see text] C2-symmetric bicyclo[2.2.2]octa-2,5-dienes containing benzyl, phenyl, and substituted phenyl groups at 2 and 5 positions were prepared enantiomerically pure by way of bicyclo[2.2.2]octane-2,5-dione as a key intermediate. These chiral diene ligands were successfully applied to rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to alpha,beta-unsaturated ketones. High enantioselectivity (up to 99% ee) as well as high catalytic activity was observed in the addition to both cyclic and linear substrates.

Catalytic arylative cyclization of alkynals has been developed by the use of phosphine-free rhodium/diene complexes as catalysts. An asymmetric variant of this process has been successfully realized by employing a C2-symmetric chiral bicyclo[2.2.2]octadiene ligand. The rhodium/diene catalyst system is also effective for arylative cyclization of other substrates such as alkynones and enynes, achieving multiple carbon-carbon bond formations in a single step.

Transition-metal-catalyzed nitrene-transfer reactions are powerful methods for incorporating nitrogen atoms directly into organic molecules. [1,2] Organic azides [2a,b] and N-sulfonyliminoiodinanes [2c-e] are highly reactive nitrene precursors, and have been widely used for such reactions as olefin aziridination and C À H amination. However, they must be handled carefully or prepared immediately before use because of their high reactivity. Therefore, the development of catalytic nitrene-transfer reactions that use stable precursors under mild reaction conditions is an important topic. Our research interest has been focused on 4H-isoxazol-5-ones, five-membered cyclic oxime esters, as candidates for stable vinylnitrene equivalents (Scheme 1). They can be readily prepared from bketoesters [3] and are generally thermally stable. We envisioned that the reaction of a 4H-isoxazol-5-one with a palladium catalyst would give a nitrene complex, [4] which is formed by the activation of the N À O bond by a low-valent palladium species [5] followed by decarboxylation. Herein, we report a palladium-catalyzed decarboxylative intramolecular aziridination reaction of alkene-tethered 4H-isoxazol-5-ones to form N-fused bicyclic aziridines.During the course of our investigations of several nitrenetransfer reactions using 4H-isoxazol-5-ones, we found that the reaction of 4H-isoxazol-5-one 1 a, which possesses a methallyl group at the 4-position, in the presence of 2.5 mol % of [Pd 2 (dba) 3 ] (5 mol % Pd) and 10 mol % of PPh 3 in 1,4-dioxane at 80 8C for 12 h gave the expected 1-azabicyclo[3

Nitrene-transfer reactions have been a powerful synthetic method for direct incorporation of nitrogen atoms into organic molecules. Discovery of novel nitrene-transfer reactions has been dominantly supported by not only the improvement in transition-metal catalysts but also by the employment of novel precursors of nitrenoids. Since the pioneering works utilizing organic azides or iminoiodinanes as practical synthetic tools for nitrogen-containing compounds were reported, a new approach using various N-heterocycles containing strain energy or a weak bond has emerged. In this review, we briefly summarize the history of nitrene-transfer chemistry from the viewpoint of its precursors. In particular, the use of N-heterocycles such as 2H-azirines, 1,4,2-dioxazol-5-ones, 1,2,4-oxadiazol-5-ones, isoxazol-5(4H)-ones, and isoxazoles are comprehensively described, showing the recent remarkable progress in this chemistry.

Chiral dienes possessing the bicyclo[2.2.2]octadiene framework were prepared readily through the [4+2] cycloaddition of (R )-α-phellandrene with methyl propiolate as the key step. Diene ( 9 ) , substituted with a tertiary alcohol on one of the two double bonds, is prepared in just one step from the cycloadduct and is highly effective as a chiral ligand for rhodium-catalyzed asymmetric conjugate addition reactions, giving the corresponding addition products with higher enantioselectivity than other chiral dienes.The recent development of chiral diene ligands for transition metal-catalyzed asymmetric reactions has opened up new vistas for ligand design. 1 Chiral dienes have been found to be superior to other types of chiral ligands, such as chiral bisphosphines, in terms of both catalytic activity and enantioselectivity, especially in rhodium-catalyzed asymmetric carbon-carbon bond forming reactions. The most effective chiral dienes reported to date for catalytic asymmetric reactions are those based on the bicyclic diene frameworks, 1-5 ,2-7 as shown in Chart 1. NOTEworthy among these is Carreira's diene (3), which has the advantage that it is readily available from an inexpensive terpene, (−)-carvone, through a 7 step sequence. 4 The development of even simpler routes to chiral diene ligands is expected to spur further advances in transition metal mediated catalytic asymmetric reactions. 1a We report here an exceedingly simple, two-step synthesis of a chiral diene from the inexpensive terpene, (R)-α-phellandrene. The new diene is highly effective as a ligand for rhodium-catalyzed asymmetric addition reactions, providing among the highest enantioselectivities reported for these reactions.thayashi@kuchem.kyoto-u.ac.jp. vrawal@uchicago.edu. ,10 1.05 equiv) was allowed to react with methyl propiolate in the presence of chlorodimethylaluminum (1.0 equiv) in dichloromethane at 0 °C for 6 h. The reaction mixture was subjected to silica gel column chromatography to give 73% isolated yield of the cycloaddition product 6, together with an Ene-type reaction product. 11 NIH Public AccessThe cycloaddition took place with high regio-and diastereoselectivity to produce bicyclo [2.2.2]octadiene (R,R,R)-6 as a single diastereoisomer (Scheme 1). The enantiomeric purity of 6, determined using a chiral stationary column (Chiralpak AD-H), was found to be 98.8 ± 0.2% ee, coincident with the purity of the commercial sample of (R)-α-phellandrene. An enantiomerically pure sample of 6 was readily obtained using preparative chiral HPLC. Alternatively, the cycloaddition can be performed with α-phellandrene of higher enantiomeric purity. 10While cycloadduct 6 can itself be used as a chiral diene ligand, the ester functionality can be easily modified to generate derivatives. Thus, reduction of 6 with HAlBu i 2 gave alcohol 7, subsequent methylation of which gave methyl ether 8. A quantitative yield of tertiary alcohol 9 was obtained by treatment of 6 with methyllithium. The corresponding ether (10) was also prepared.(1) Chiral dienes ...