Tomoko Yajima

ASYMMETRIC CATALYSIS OF CARBONYL-ENE AND ALDOL REACTIONS WITH FLUORAL BY CHIRAL BINAPHTHOL-DERIVED TITANIUM COMPLEX

Abstract The chiral titanium complex-catalyzed ene-type reaction and the Mukaiyama aldol reaction with fluoral are shown to serve as an efficient route to the enantioselective and diastercoselective synthesis of CF 3 -substituted components of biological and synthetic importance.

Radical-mediated hydroxytrifluoromethylation of α,β-unsaturated esters

Treatment of α,β-unsaturated esters with trifluoromethyl iodide and triethylborane in the presence of KF and H 2 O gave the corresponding hydroxytrifluoromethylated esters.

Asymmetric catalysis of ene-type reaction with fluoral by chiral titanium complex: A semi-empirical and ab-initio analysis of ene reactivity

Abstract The chiral titanium complex-catalyzed ene-type reaction with fluoral is shown to serve as an efficient route for the asymmetric synthesis of CF 3 -substituted compounds of biological and synthetic importance in extremely high enantiomeric excesses (>95% ee). The ene reactivity of trihaloacetaldehyde including fluoral is estimated in terms of the balance of LUMO energy level vs . electron density on the carbonyl carbon.

Spontaneous Enantiomeric Resolution in a Fluid Smectic Phase of a Racemate.

Right- and left-handed homochiral domains segregate in a fluid smectic phase of the racemic (R*,S*)-beta-Me-TFMHPOBC analogue shown. This CF(3)-containing liquid crystalline compound exhibits an electrooptic response in a homogeneous cell, although no macroscopic dipole is expected to exist. Moreover, the homeotropic cells of this material exhibit striped domains, which are associated with fine stripes having two opposite tilt senses with respect to the predominant stripes.

Asymmetric imine-ene reactions with chiral glyoxylate-derived α-imino esters : an efficient route to asymmetric synthesis of α-amino acids

Abstract The asymmetric ene reactions with α-imino esters, prepared from (−)-8-phenylmenthyl glyoxylate, are shown to provide an efficient entry to the asymmetric synthesis of α-amino acids.

Diastereoselective and enantioselective catalysis of the carbonyl-ene reaction with fluoral

Abstract The chiral titanium complex-catalyzed carbonyl-ene reaction with fluoral is shown to serve as an efficient route for the syn-diastereoselective and enantioselective synthesis of CF3-substituted compounds of biological and synthetic importance.

Chiroptical Studies on Supramolecular Chirality of Molecular Aggregates

The attempts of applying chiroptical spectroscopy to supramolecular chirality are reviewed with a focus on vibrational circular dichroism (VCD). Examples were taken from gels, solids, and monolayers formed by low-molecular mass weight chiral gelators. Particular attention was paid to a group of gelators with perfluoroalkyl chains. The effects of the helical conformation of the perfluoroalkyl chains on the formation of chiral architectures are reported. It is described how the conformation of a chiral gelator was determined by comparing the experimental and theoretical VCD spectra together with a model proposed for the molecular aggregation in fibrils. The results demonstrate the potential utility of the chiroptical method in analyzing organized chiral aggregates.

Remote substituent effect favoring the formation of syn-adducts in the chelation controlled radical reactions of γ-benzyloxy-α-methylenecarboxylic acid esters

The chelation controlled radical reactions of ethyl γ-benzyloxy-α-methylenecarboxylates bearing a bulky γ-substituent, such as CHMe2, CHPh2, c-C6H11 and CH(Ph)OTBDMS, with alkyl iodides gave the syn-adducts with high diastereoselectivities. However, the diastereoselectivity for the substrates bearing a γ-substituent CH(i-Pr)OTBDMS depended critically on the configuration of the substituent; the substrate bearing the OTBDMS group anti to the γ-benzyloxy group showed poor diastereoselectivity, but its diastereomer gave syn-adduct exclusively. The high syn-selectivitiy is referred to the H-atom transfer to the outside face of radical center in the sharply folded seven-membered chelate intermediate bearing the ethoxy group with Z-geometry. The corner flapping of the radical center atom of the global minimum energy conformer generates a local minimum conformer and the H-atom transfer to the outside face of the radical center of the newly formed structure gives the anti-adduct. The poor diastereoselectivity is due to the very small energy difference between the two conformers and consequently both the syn- and anti-adducts are yielded in nearly equal amounts.

Terminal effects on gelation by low molecular weight chiral gelators

Gel formation by low molecular mass gelators was investigated. The gelator was trans(RR)- or trans(SS)-N,N′-n-bromoalkanoyl-1,2-diaminocyclohexane (denoted as RR-CnBr or SS-CnBr, respectively; n = the number of carbon atoms in an alkanoyl group). When n was varied from 5 to 12, the gelators formed transparent or opaque or turbid gels in benzene except for n = 8. Focusing on the end effects, the gelation behavior of CnBr was compared with that of non-brominated counterparts (denoted as RR- or SS-Cn). From the vibrational circular dichroism (VCD) spectra of enantiomeric gelator/benzene-d6 gels, the signs of the coupled peaks around 1640 cm−1, which were assigned to the symmetric and asymmetric CO stretching vibrations from the higher to lower wavenumber, respectively, were opposite between SS-CnBr and SS-Cn (or between RR-CnBr and RR-Cn). On the other hand, the signs of the coupled peaks around 1550 cm−1 assigned to the NH stretching vibrations remained unaffected. The observed reversal of the signs in the CO couplet was rationalized in terms of the different modes of stacking in fibrils. In the case of Cn, for example, the molecules were stacked through anti-parallel double intermolecular hydrogen bonds using two pairs of >NH and >CO groups, while, in the case of CnBr, a single intermolecular hydrogen bond was formed with the remaining pair of >NH and >CO groups forming an intramolecular hydrogen bond. Single crystal X-ray analyses were performed for SS-C6Br and SS-C8Br. The results demonstrated that the length of the bromoalkanoyl chains drastically affected the packing modes in crystalline states.

Development of novel synthetic routes to bis(perfluoroalkyl)-substituted anthracene derivatives

Commercially available anthraquinones were smoothly converted to either symmetrically or unsymmetrically substituted 9,10-bis(perfluoroalkyl)anthracene-9,10-diols by way of bistrifluoromethylation or successive trifluoromethylation-nucleophilic perfluoroalkylation, respectively, and these diols can be easily aromatized to form bis(perfluoroalkyl)anthracene derivatives in good yields by treatment with a mixture of CBr4 and PPh3. Further cross-coupling reactions using halogen-containing anthracene derivatives realized a successful extension of the original π-conjugation systems.