Ahighly diastereo-and enantioselective method for the epoxidation of aldehydes with a-diazoacetamides has been developed with two different borate ester catalysts of VA NOL. Both catalytic systems are general for aromatic,aliphatic, and acetylenic aldehydes,g iving high yields and inductions for nearly all cases.One borate ester catalyst has two molecules of VA NOL and the other only one VA NOL. Catalysts generated from BINOL and VA POL are ineffective catalysts.A n application is shown for access to the side-chain of taxol.The tactical repertoire for the conversion of either an aldehyde or ketone into an epoxide largely consists of two transformations (Scheme 1): 1) the Darzens condensation of an a-halo stabilized carbanion with the ac arbonyl compound, [1,2] 2) the Corey-Chaykovskyr eaction which involves as ulfur ylide as ac arbene surrogate in the synthesis of epoxides. [3][4][5][6][7] At hird method involving the formation of epoxides from the reactions of diazo compounds are not that common and have not been particularly useful. [8][9][10] However, Scheme 1. Epoxidesf rom ketones and aldehydes.EWG = electron-withdrawing group.Scheme 2. The cis-and trans-aziridination with BOROX catalysts.

We report herein an efficient aluminum-catalyzed asymmetric MPV reduction of ketones with broad substrate scope and excellent yields and enantiomeric inductions. A variety of aromatic (both electron-poor and electron-rich) and aliphatic ketones were converted to chiral alcohols in good yields with high enantioselectivities (26 examples, 70−98% yield and 82−99% ee). This method operates under mild conditions (−10 °C) and low catalyst loading (1−5 mol %). Furthermore, this process is catalyzed by the earth-abundant main-group element aluminum and employs 2-propanol as the hydride source.

Given the sudden and unexplained rise in the cost of (+)- and (−)-sparteine, an alternative method for the resolution of vaulted biaryls has been developed. This method involves the reaction of a racemic vaulted biaryl ligand with one equivalent of BH3·SMe2 and one equivalent of either quinine or quinidine. A precipitate then forms from the resulting mixture of diastereomeric borates as a result of differential solubilities. Hydrolysis of the precipitate then liberates the (S)-ligand in the case of quinine and the (R)-ligand in the case of quinidine, both with >99% ee. This method has been applied to 16 different vaulted biaryl ligands, including 10 whose preparation is described here for the first time. In addition, proof of principle has been demonstrated for the dynamic thermodynamic resolution of the vaulted biaryl ligands with this method in combination with a nonchiral copper­(II) complex that can racemize the ligand.

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.

This report presents a structure-guided approach for the optimization of VANOL-derived imidodiphosphorimidates as catalysts for the halonium-ion-induced spiroketalization reaction. Fine tuning of the catalyst active site, alongside enhanced acidity, were required to achieve high catalytic activity for the spiroketalization reaction. A wide range of substrates were well tolerated yielding halogenated spiroketals in high yields, diastereoselectivities, and enantioselectivities.