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Thermoelectric (TE) materials are promising candidates for solving today's energy problem owing to their ability to directly convert waste heat into electricity via the Seebeck effect. One of the most efficient TE materials known is Zn4Sb3. To understand its high efficiency, a novel composite crystal structure model for β- and γ-phases of Zn4Sb3 is constructed using a (3 + 1)-dimensional ((3 + 1)-D) superspace group approach. This (3 + 1)-D model is expressed as [Zn3+δSb][Sb]p with the superspace group of R3¯m(00γ)0s. The [Zn3+δSb] and [Sb] subsystems have same a- and b-axis lengths but a different c-axis length. The (3 + 1)-D model contains four atomic sites: a Zn(1) normal site, an interstitial Zn (Zni) site and an Sb(1) site in the [Zn3+δSb] subsystem and an Sb(2) site in the [Sb] subsystem, which is different from a conventional 3D model containing additional Zni sites. The crystal structures of β- and γ-Zn4Sb3 are investigated via powder and synchrotron X-ray diffraction (XRD) measurements. The XRD patterns are well analysed by the (3 + 1)-D model. The occupancies of Zn(1), Sb(1) and Sb(2) sites are 100%, whereas the Zni occupancy changes depending on the heating time during the preparation of β-Zn4Sb3. Moreover, electronic density of states (DOS) of β-Zn4Sb3 with and without Zni is calculated based on the (3 + 1)-D model, demonstrating a close relationship between the DOS and the Zni occupancy. The calculated TE properties, such as Seebeck coefficient, electrical conductivity and power factor, also depend on the Zni occupancy. [ABSTRACT FROM AUTHOR]

Enantioselective alkynylation of C(sp3)-H bonds adjacent to a nitrogen atom has been achieved using only chiral p-tolyl tert-butyldimethylsilylethynyl sulfoximine and benzophenone under photo-irradiation conditions. A twocarbon alkyne unit was chemo- and enantioselectively transferred at the nitrogen-substituted methylene to produce the optically active propargylic amines of various structures. Remarkably, the NH-unprotected sulfoximine group efficiently transmits its stereochemical information to the product and functions as a traceless chiral auxiliary. [ABSTRACT FROM AUTHOR]

A general and practical synthetic protocol for the direct transformation of unreactive C(sp³)-H bonds to C(sp³)-CN bonds has been developed. The homolytic cleavage of the C-H bond is initiated by photo-excited benzophenone, and the resulting carbon radical subsequently reacts with tosyl cyanide to afford the corresponding nitrile in a highly efficient manner. The present methodology is widely applicable to various starting materials including ethers, alcohols, amine derivatives, alkanes, and alkylbenzenes. This newly developed C-H cyanation protocol provides a powerful tool for selective one-carbon elongation for the construction of architecturally complex molecules. [ABSTRACT FROM AUTHOR]

The functionalization of aliphatic C-H bonds is achieved by direct photolytic cyanation with TosCN. [ABSTRACT FROM AUTHOR]

1-Hydroxytaxinine (1) is a cytotoxic taxane diterpenoid. Its central eight-membered B-ring possesses four oxygen-functionalized centers (C1, C2, C9, and C10) and two quaternary carbon centers (C8 and C15), and is fused with six-membered A- and C-rings. The densely functionalized and intricately fused structure of 1 makes it a highly challenging synthetic target. Reported here is an efficient radical-based strategy for assembling 1 from A- and C-ring fragments. The A-ring bearing an α-alkoxyacyl telluride moiety underwent intermolecular coupling with the C-ring fragment by a Et 3 B/O 2 -promoted decarbonylative radical formation. After construction of the C8-quaternary stereocenter, a pinacol coupling reaction using a low-valent titanium reagent formed the B-ring with stereoselective installation of the C1,C2-diol. Subsequent manipulations at the A- and C-rings furnished 1 in 26 total steps., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Herein, we report a new synthetic route from (S)-pyroglutaminol to (+)-lactacystin, a potent inhibitor of the 20S proteasome. The photoinduced intermolecular C(sp(3))-H alkynylation and intramolecular C(sp(3))-H acylation chemo- and stereoselectively constructed the tetra- and trisubstituted carbon centers, respectively. The obtained bicycle was transformed into the target compound in a concise manner. The present total synthesis demonstrates the power of the direct C(sp(3))-H functionalizations for the assembly of multiple functionalized structures of natural products.

Enantioselective alkynylation of C(sp(3) )H bonds adjacent to a nitrogen atom has been achieved using only chiral p-tolyl tert-butyldimethylsilylethynyl sulfoximine and benzophenone under photo-irradiation conditions. A two-carbon alkyne unit was chemo- and enantioselectively transferred at the nitrogen-substituted methylene to produce the optically active propargylic amines of various structures. Remarkably, the NH-unprotected sulfoximine group efficiently transmits its stereochemical information to the product and functions as a traceless chiral auxiliary., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)