Catalytic Asymmetric Aziridination of Benzhydryl Imines and Diazoacetate­ Esters with BOROX Catalysts from 3,3′-Disubstituted VANOL Ligands

Abstract

<jats:p>This work details the synthesis of 22 new chiral VANOL ligands that differ by the nature of the substituent in the 3- and 3′-positions of the ligand. These ligands were incorporated into boroxinate catalysts that were used to screen the catalytic asymmetric aziridination of benzhydryl imines with ethyl diazoacetate. Each catalyst was screened in the reaction of imines generated from benzaldehyde and cyclohexanecarboxaldehyde and some with 4-nitro- and 4-methoxybenzaldehyde. In addition, the first report of the effect of the ester substituent of the diazoacetate ester on the asymmetric induction in these aziridination reactions is presented. The first X-ray structure of a boroxinate catalyst generated from a VANOL-derived ligand is also reported.</jats:p>

Structure Guided Design of VANOL-Imidodiphosphorimidate Catalysts for the Catalytic Enantioselective Bromospiroketalization Reaction

“…As depicted in Figure , the “major groove” of the vaulted systems resides in the center of the molecule. We anticipated that the activation of the halenium source via proton delivery from the triflimide occurs in this region, and thus surmised a larger binding cavity might allow for a more structured arrangement of the reaction components. − ,− VAPOL imidodiphosphorimidate (2a) 2 -D was prepared from VAPOL and (triflyl)­phosphorimidoyl trichloride following reported procedures for BINOL catalysts and was evaluated as the catalyst for the bromospiroketalization of 4a . The desired product 5a was obtained in good yield but low er (Figure ).…”

“Homoleptic” Tetracoordinate Boron Compounds

“…Wulff et al developed a family of VANOL/VAPOL-derived chiral borate ester catalysts named BOROX . These catalysts were readily prepared from the chiral VANOL/VAPOL diphenols and B­(OPh) 3 or BH 3 ·SMe 2 (Scheme ).…”