Evaluation of a chiral cubane-based Schiff base ligand in asymmetric catalysis reactions

• Kyle F. Biegasiewicz,
• Michelle L. Ingalsbe,
• Jeffrey D. St. Denis,
• James L. Gleason,
• Junming Ho,
• Michelle L. Coote,
• G. Paul Savage and
• Ronny Priefer

Beilstein J. Org. Chem. 2012, 8, 1814–1818, doi:10.3762/bjoc.8.207

• cyclopropanation and Michael addition reactions. Although there was no increase in stereocontrol, upon computational evaluation using both M06L and B3LYP calculations, it was revealed that a pseudo six-membered ring exists, through H-bonding of a cubyl hydrogen to the copper core. This decreases the steric bulk

• above the copper center and limits the asymmetric control with this ligand. Keywords: chiral ligand; cubane; M06L and B3LYP calculations; Michael addition; Introduction Since the initial synthesis of cubane in 1964 by Eaton and Cole [1][2], numerous studies have been undertaken on its derivatives

• are well within the required H-bonding length of <3.2 Å [31]. In addition, the C…Cu lengths of 2.85 and 3.03 Å with M06L and B3LYP, respectively, were well within the required 4.0 Å limit [31]. This produces pseudo six-membered rings having a C–H…Cu bond angle of 125.1° or 122.9° with M06L and B3LYP