Rhodium-Catalyzed Cascade Reaction of 1,6-Enynes Involving Addition, Cyclization, and β-Oxygen Elimination

Synthesis and reactivity of boryloxorhodium complexes. Relevance to intermolecular transmetalation from boron to rhodium in Rh-catalyzed reactions

The synthesis of a dimeric boryloxorhodium complex having the Rh-O-Bpin scaffold from the reaction of [(cod)Rh(OMe)]2 or [(cod)Rh(OH)]2 with an arylboronate has been achieved. The obtained dirhodium complex is converted into mononuclear complex [(cod)Rh(OBpin)(PPh3)], which reacts with arylboronic acid to afford the complex with an Rh-aryl bond via transmetalation from boron to rhodium. The dimeric boryloxorhodium complex catalyzes the 1,4-addition of arylboronic acid to cyclohexene-2-one.

Enantioselective Nickel-Catalyzed Intramolecular Allylic Alkenylations Enabled by Reversible Alkenylnickel E/Z Isomerization

Enantioselective nickel-catalyzed arylative cyclizations of substrates containing a Z-allylic phosphate tethered to an alkyne are described. These reactions give multisubstituted chiral aza- and carbocycles, and are initiated by the addition of an arylboronic acid to the alkyne, followed by cyclization of the resulting alkenylnickel species onto the allylic phosphate. The reversible E/Z isomerization of the alkenylnickel species is essential for the success of the reactions.

Rhodium-catalysed arylative annulation of 1,4-enynes with arylboronic acids

Rhodium(i)-catalysed arylative annulation of 1,4-enynes with arylboronic acids affords 1,1-disubstituted 3-(arylmethylene)indanes via an addition–1,4-rhodium migration–addition sequence.

Remote C-H activation via through-space palladium and rhodium migrations

The catalytic activation of a C-H bond is a fundamentally important organic transformation. There are now numerous reports of palladium-mediated C-H activation by the through-space interaction of a palladium center with a neighboring C-H bond. This type of C-H activation can lead to a net "palladium migration" from the carbon atom where the palladium is first introduced to a remote carbon atom where C-H activation occurs. This process provides a novel method to introduce a palladium moiety into a position where direct palladium introduction may not be straightforward. This process is accompanied by concurrent migration of a hydrogen atom in the direction opposite to that of the palladium migration. Analogous rhodium migrations have also been reported. In this account, different types of palladium and rhodium migrations are reviewed and the reaction mechanism is discussed.

Rh(I)-Catalyzed Carbonylative Cyclization Reactions of Alkynes with 2-Bromophenylboronic Acids Leading to Indenones

The Rh-catalyzed reaction of alkynes with 2-bromophenylboronic acids involves carbonylative cyclization to give indenones. The key steps in the reaction involve the addition of an arylrhodium(I) species to an alkyne and the oxidative addition of C-Br bonds on the adjacent phenyl ring to give vinylrhodium(I) species II. The regioselectivity depends on both the electronic and the steric nature of the substituents on the alkynes. A bulky group and an electron-withdrawing group favor the -position of indenones. In the case of silyl- or ester-substituted alkynes, the regioselectivity is extremely high. The selectivity increases in the order SiMe3 > COOR >> aryl >> alkyl. The reaction of norbornene with 2-bromophenylboronic acids under 1 atm of CO gives the corresponding indanone derivative. The reaction of alkynes with 2-bromophenylboronic acids under nitrogen gives naphthalene derivatives, in which two molecules of alkynes are incorporated. A vinylrhodium complex similar to II can also be generated by a different route by employing 2-bromophenyl(trimethylsilyl)acetylene and arylboronic acids in the presence of Rh(I) complex as the catalyst, resulting in the formation of indenones. The reaction of 1-(2-bromophenyl)-hept-2-yn-1-one with PhB(OH)2 in the presence of Rh(I) complex also resulted in carbonylative cyclization to give an indan-1,3-dione derivative.