The phosphates R-Sr(PO 3 ) 2 , SrZn(P 2 O 7 ), and R-Sr 2 (P 2 O 7 ) were doped and codoped with Eu 2+ and Mn 2+ , structurally characterized, and analyzed by fluorescence spectroscopy. R-Sr(PO 3 ) 2 was found to enable the energy transfer between Eu 2+ and Mn 2+ , leading to a new phosphor emitting at 404 and 625 nm and giving white light under excitation at 323 nm. In SrZn(P 2 O 7 ) and R-Sr 2 (P 2 O 7 ), the codoping was also successful but the luminescence intensity of the red emission was found to be less intense. Moreover, the crystal structure of SrZn(P 2 O 7 ) has been determined based on single-crystal data (P2 1 /n, Z ) 4, a ) 531.43(2) pm, b ) 820.80(3) pm, c ) 1272.50(6) pm, β ) 90.192(4)°, R1 ) 0.035, and wR2 ) 0.070).
Free choice: Carboxamides of bispicolylamine are alternative protecting groups for carboxylic acids (see scheme). As a consequence of their straightforward applicability, their high chemical stability towards a broad range of conditions, and their selective cleavage under mild conditions to give either carboxylic acids or their methyl esters, this new protection method should find widespread application in the realm of organic synthesis.
A unified synthetic strategy for the asymmetric syntheses of the natural products diversonol and lachnone C was developed by using the domino vinylogous aldol-oxa-Michael reaction as the enantioselective key step. Further transformations include dihydroxylation, lactol-opening by a Wittig-reaction, and lactonization. The obtained chromone lactones, a class of mycotoxins, can further be converted to tetrahydroxanthones by a Dieckmann condensation. This general method allows for the first time the enantioselective access to these classes of natural products and should be applicable to other members of the tetrahydroxanthone and chromone lactone families.
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