“Head-to-head” dimerization and dehydrodimerization of vinyl ketones catalyzed by modified rhodium(I) complexes

A Rhodium‐Catalyzed Tandem Alkyne Dimerization/ 1,4‐Addition Reaction

“…The use of the electron‐rich phosphines tris( para ‐methoxyphenyl)phosphine (Table 1, entry 2) and tris(2,4,6‐trimethoxyphenyl)phosphine (entry 3) led to a competing reaction, dimerizing the MVK to form the Baylis–Hillman product 4 (Figure 1). Both rhodium complexes12 and phosphines13 have been reported to dimerize enones, forming 1,5‐diketones like 4 , so either the phosphine or the rhodium complex formed with these phosphines may be responsible for this mode of reactivity. The use of 1,2‐bis(diphenylphosphino)benzene as a ligand (entry 10) failed to give either alkyne 2 or enyne 3 but instead gave the O ‐Michael addition product 5 (Figure 1).…”

Ruthenium-catalyzed stereo- and chemoselective oxidative coupling of vinyl ketones: efficient access to (E,E)-1,6-dioxo-2,4-dienes

“…A plausible reaction mechanism for the oxidative coupling reaction between vinyl ketones is depicted in Scheme 4. 15 Initially, the catalytic cycle starts with an abstraction of chlorides from the [Ru( p -cymene)Cl 2 ] 2 by AgSbF 6 in the presence of Cu(OAc) 2 leading to the formation of a reactive species A . Coordination of both the activated olefins to species A followed by subsequent regioselective cycloruthenation would lead to the formation of a five-membered ruthenacycle C .…”

Ruthenium-Catalyzed Direct Dehydrogenative Cross-Coupling of Allyl Alcohols and Acrylates: Application to Total Synthesis of Hydroxy β-Sanshool, ZP-Amide I, and Chondrillin

“…Based on the above result and literature support, a plausible reaction mechanism for the ruthenium-catalyzed coupling reaction is depicted in Scheme . ,, The catalytic cycle is initiated by hydroxy group coordination to in situ generated reactive cationic ruthenium complex RuX 2 L ( A ), followed by β-hydride elimination which would produce a ruthenium hydride species ( C ). In the presence of activated olefins, the intermediate ( C ) could undergo reductive elimination followed by oxidative addition of both the olefins leading to the formation of a five-membered ruthenacycle ( E ).…”