Conica can: The In(OTf)3‐catalyzed cyclization of nitrogen‐ and oxygen‐tethered acetylenic malonic esters gives five‐ to seven‐membered heterocycles in moderate to excellent yields (see scheme; Tf=trifluoromethanesulfonyl). The asymmetric synthesis of (−)‐salinosporamide A illustrates the synthetic utility of the method.
An asymmetric 1,4-addition reaction of 5H-oxazol-4-ones with alkynyl carbonyl compounds was developed, and, for the first time, high enantiomeric and geometric control was achieved to afford the thermodynamically unstable Z-isomer predominantly using chiral guanidine catalysts bearing a hydroxy group at the appropriate position. The method provides synthetically useful γ-butenolide ester bearing a chiral quaternary stereogenic center.
The authors characterized polycrystalline samples of Sn-doped ErNiSb “ErNiSnxSb1−x (x=0, 0.01, 0.03, and 0.05)” to develop p-type half-Heusler thermoelectric materials. All samples prepared in this study exhibited positive Seebeck coefficients. With increasing Sn content x, the carrier concentration increased, leading to decreases in both electrical resistivity (ρ) and the Seebeck coefficient (S). Thermal conductivity (κ) values were at a similar level in all of the compositions. Sn-doping improved the thermoelectric figure of merit ZT(=S2T∕ρ∕κ) of ErNiSb; the maximum ZT value was 0.29 at 669K, obtained in the composition ErNiSn0.01Sb0.99.
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