Pentamethylcyclopentadienyl–Ruthenium Catalysts for Regio‐ and Enantioselective Allylation of Nucleophiles

Abstract

Ruthenium(II) complexes containing the pentamethylcyclopentadienyl ligand efficiently perform the activation of allylic carbonates and halides to generate cationic and dicationic ruthenium(IV) complexes. This activation has been transferred as a key step to the catalytic allylation of nucleophiles. The structural and electronic properties of the allylic moieties lead to the regioselective formation of chiral products resulting from nucleophilic addition to their most substituted terminus. The catalytic activity of various Ru(Cp*) precatalysts in several allylic substitutions by C and O nucleophiles will be presented. The enantioselective version that has been demonstrated by using optically pure bisoxazoline ligands will also be discussed.

Novel [Ruthenium(substituted‐tetramethylcyclopentadiene) (2‐quinolinecarboxylato)(allyl)] Hexafluorophosphate Complexes as Efficient Catalysts for Highly Regioselective Nucleophilic Substitution of Aliphatic Allylic Substrates

“…[2] Furthermore, the substitution of one or two acetonitrile ligands in the cationic complex 1a by various nitrogen [3] or phosphorus [4] ligands (Scheme 1) has led to a family of precatalysts allowing one to extend the scope of the catalytic process and to enhance reactivity. [5] Thus, the regioselective formation of branched derivatives from aromatic cinnamyl-type linear substrates is almost perfect in several reactions involving carbon-carbon, oxygen-carbon, and nitrogen-carbon bond formation. However, the regioselectivity remained unsatisfactory starting from unsymmetrical aliphatic allylic substrates.…”

“…Since the discovery of the catalytic activity of the [RuA C H T U N G T R E N N U N G (C 5 Me 5 )(1,5-cyclooctadiene)Cl] complex in nucleophilic allylic substitution, [1] the precatalyst [RuA C H T U N G T R E N N U N G (C 5 Me 5 6 ], 1a, has attracted the most interest as it provided higher regioselectivities in favor of the chiral branched products. [2] Furthermore, the substitution of one or two acetonitrile ligands in the cationic complex 1a by various nitrogen [3] or phosphorus [4] ligands (Scheme 1) has led to a family of precatalysts allowing one to extend the scope of the catalytic process and to enhance reactivity.…”

Ruthenium Catalyzed Selective Regio‐and‐Mono‐Allylation of Cyclic 1,3‐Diketones Using Allyl Alcohols as Substrates

“…The use of transition metal catalysts to facilitate the allylation of a variety of organic nucleophiles now represents an established methodology with examples from Pd, [1] Ir, [2] Cu [3] and Ru [4][5][6][7][8][9][10] chemistry all well documented [see Eq. (1)].…”

“…[5][6][7][8][9][10] Furthermore, additives, such as a base, in stoichiometric quantities are often necessary in order to generate an anionic nucleophile to ensure that the chemistry proceeds in good yield. [11][12][13][14] Even under such conditions, the reactions are often observed to be relatively slow, requiring 10-20 h [7,15a] and/or increased reaction temperatures [11,12] to go to completion.…”

Enantio- and regioselective CpRu-catalyzed Carroll rearrangement

“…In this respect, several ruthenium derivatives have proven to be largely effective for the introduction of nucleophiles at the more substituted position leading to branched (b) rather than linear (l) products (eq. 1) and Cp*Ru derivatives in particular [2].…”