Enantiomer-selective carbamoylation of racemic alpha-hydroxy gamma-lactones with half equivalents of isocyanates in the presence of chiral Cu(II) catalysts was studied. Among a series of catalyst bearing chiral bis(oxazoline) (box) and pyridine(bisoxazoline) ligands, [Cu(tBu-box)]X(2) [X=OSO(2)CF(3) (3 a), SbF(6) (3 b)] showed the highest enantioselectivity in the reaction of pantolactone (1 a). Use of n-C(3)H(7)NCO, a small alkyl isocyanate, in CH(2)Cl(2) solution was important to achieve a high level of enantiomer selection. The tBu-box-Cu(II) catalyst efficiently differentiated two enantiomers of beta-substituted alpha-hydroxy gamma-lactones under the optimized reaction conditions, resulting in a stereoselectivity factor (s=k(fast)/k(slow)) of up to 209. Furthermore, this catalyst is highly active, so that the carbamoylation can be conducted with a substrate-to-catalyst molar ratio of 2000-3000. A catalytic cycle of this reaction is also proposed.
The
charge-transfer (CT) complex 3,3′,5,5′-tetramethylbendizine-7,7,8,8-tetracyanoquinodimethane
was found to display the thermosalient effect, in which crystals exhibit
mechanical responses due to temperature changes. Such responses are
rarely observed with CT complexes. Furthermore, while this crystalline
complex was known to have an interesting phase transition in which
the charge distribution changes at low temperatures, some of the physical
properties of single crystals of the material were unknown, because
the crystal is broken during the thermosalient event. In this study,
we used a polymer-coating method to prevent cracking of the crystal,
allowing us to observe drastic changes in resistivity and ferroelectric-like
dielectric response accompanied by the phase transition at low temperature.
This result suggests that organic solids with mechanical response
and electric and magnetic functions can be produced, since CT complexes
exhibit various electric and magnetic functions and physical properties.
Kinetic resolution of sterically hindered racemic α-tert-alkyl-α-hydroxy esters is performed by enantiomer-selective carbamoylation with the t-Bu-Box-Cu(II) catalyst (Box = bis(oxazoline)). The reaction with 0.5 equiv of n-C(3)H(7)NCO is carried out with a substrate-to-catalyst molar ratio of 500-5000 at -20 to 25 °C. The high enantiomer-discrimination ability of the catalyst achieves an excellent stereoselectivity factor (s = k(fast)/k(slow)) of 261 in the best case. A catalytic cycle for this reaction is proposed.
Die Alkylierung von Benzol mit den optisch aktiven Titelverbindungen (I) in Gegenwart von AlCl3 führt zu den entsprechenden 3‐Phenyl‐substituierten Derivaten (II) in guten optischen Ausb. (14‐54%).
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