Axially Chiral N‐Oxide Catalysts for the Allylation and Crotylation of Aromatic Aldehydes: Exploiting Nonlinear Effects

• Published in: ChemCatChem 2024-11, Vol.16 (21), p.n/a
• Main Authors: Romero‐Arenas, Antonio, Ramírez‐López, Pedro, Iglesias‐Sigüenza, Javier, Fernández, Rosario, Ros, Abel, Lassaletta, José M.
• Format: Article
• Language: English
• Subjects: Aldehydes; Allyl compounds; Allylation; Catalysts; Chemical reactions; Chemical synthesis; N-oxides; Nonlinear effects; Organocatalysis; Trichlorosilanes
• ISSN: 1867-3880; 1867-3899
• DOI: 10.1002/cctc.202400806

A new family of IAN‐type amine N‐oxides is presented as catalysts for the allylation and crotylation of aromatic aldehydes with allyltrichlorosilanes. These reaction exhibit a remarkably positive nonlinear effect which enables utilization of the catalysts in subenantiopure form. As enantiopure catalysts are not required under this regime, the synthesis of these N‐oxides is straightforward through catalytic asymmetric synthesis, avoiding lenghty synthesis from the chiral pool or resolution of diastereoisomers. Studies of the corresponding crotylation with Z‐ and E‐crotylsilanes suggest that the reaction proceeds through a chair‐like transition state. IAN‐type N‐oxides (IAN=Isoquinoline‐Amino Naphthalene) exhibit a strong nonlinear effect that has been exploited to perform highly enantioselective allylations and crotylations of aromatic aldehydes featuring diverse electronic character. The crystallization in the reaction media of the heterochiral dimer, stabilized through hydrogen bonding between the N−O and the acidic C(3)−H of the isoquinoline ring explains the observed nonlinear effect.