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.

VANOL and VAPOL ligands are known to react with three equivalents of B(OPh) to form a catalytic species that contains a boroxinate core with three boron atoms, and these have proven to be effective catalysts for a number of reactions. However, it was not known whether the closely related BINOL ligand will likewise form a boroxinate species. It had simply been observed that mixtures of BINOL and B(OPh) were very poor catalysts compared to the same mixtures with VANOL or VAPOL. Borate esters of BINOL have been investigated as chiral catalysts, and these include meso-borates, spiro-borates, and diborabicyclo-borate esters. Borate esters are often in equilibrium, and their structures can be determined by stoichiometry and/or thermodynamics, especially in the presence of a base. The present study examines the structures of borate esters of BINOL that are produced with different stoichiometric combinations of BINOL with B(OPh) in the presence and absence of a base. Depending on conditions, pyro-borates, spiro-borates, and boroxinate species can be generated and their effectiveness in a catalytic asymmetric aziridination was evaluated. The finding is that BINOL borate species are not necessarily inferior catalysts to those of VANOL and VAPOL but that, under the conditions, BINOL forms two different catalytic species (a boroxinate and a spiro-borate) that give opposite asymmetric inductions. However, many BINOL derivatives with substitutents in the 3- and 3'-positions gave only the boroxinate species and the 3,3'-PhBINOL ligand gave a boroxinate catalyst that gives excellent inductions in the aziridination reaction. BINOL derivatives with larger groups in the 3,3'-position will not form either spiro-borates or boroxinate species and thus are not effective catalysts at all.

An enantioselective Pd /Brønsted acid-catalyzed carbonylative carbocyclization of enallenes ending with a cross-dehydrogenative coupling (CDC) with a terminal alkyne was developed. VAPOL phosphoric acid was found as the best co-catalyst among the examined 28 chiral acids, for inducing the enantioselectivity of α-chiral ketones. As a result, a number of chiral cyclopentenones were easily synthesized in good to excellent enantiomeric ratio with good yields.

An enantioselective Pd II /Brønsted acid-catalyzed carbonylative carbocyclization of enallenes ending with ac ross-dehydrogenative coupling (CDC) with at erminal alkyne was developed. VA POL phosphoric acid was found as the best co-catalyst among the examined 28 chiral acids,f or inducing the enantioselectivity of a-chiral ketones.Asaresult, anumber of chiral cyclopentenones were easily synthesized in good to excellent enantiomeric ratio with good yields. Scheme 1. Approaches to introduce chirality at a-position of carbonyl groups. L* = chiral ligand. LG = leaving group. [X*] À = chiral anion. CPA = chiral phosphorica cid.

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.