《Enantioselective C-H Lactonization of Unactivated Methylenes Directed by Carboxylic Acids》 was written by Cianfanelli, Marco; Olivo, Giorgio; Milan, Michela; Klein Gebbink, Robertus J. M.; Ribas, Xavi; Bietti, Massimo; Costas, Miquel. HPLC of Formula: 624-28-2 And the article was included in Journal of the American Chemical Society in 2020. The article conveys some information:
The formidable challenges of controlling site-selectivity, enantioselectivity, and product chemoselectivity make asym. C-H oxidation a generally unsolved problem for nonenzymic systems. Discrimination between the two enantiotopic C-H bonds of an unactivated methylenic group is particularly demanding and so far unprecedented, given the similarity between their environments and the facile overoxidn. of the initially formed hydroxylation product. Here we show that a Mn-catalyzed C-H oxidation directed by carboxylic acids can overcome these challenges to yield γ-lactones in high enantiomeric excess (up to 99%) using hydrogen peroxide as oxidant and a Bronsted acid additive under mild conditions and short reaction times. Coordination of the carboxylic acid group to the bulky Mn complex ensures the rigidity needed for high enantioselectivity and dictates the outstanding γ site-selectivity. When the substrate contains nonequivalent γ-methylenes, the site-selectivity for lactonization can be rationally predicted on the basis of simple C-H activation/deactivation effects exerted by proximal substituents. In addition, discrimination of diastereotopic C-H bonds can be modulated by catalyst design, with no erosion of enantiomeric excess. The potential of this reaction is illustrated in the concise synthesis of a tetrahydroxylated bicyclo[3.3.1]nonane enabled by two key, sequential γ-C-H lactonizations, with the latter that fixes the chirality of five stereogenic centers in one step with 96% ee. In the part of experimental materials, we found many familiar compounds, such as 2,5-Dibromopyridine(cas: 624-28-2HPLC of Formula: 624-28-2)
2,5-Dibromopyridine(cas: 624-28-2) belongs to pyridine. Pyridine is a relatively complex molecule and exhibits a number of different bands in IR spectra. Among others, the bands characterizing the ν8a and ν19b modes have been found to be sensitive to the coordination or protonation of the molecule. Note that the band that is diagnostic for the PyH+ ion at about 1545 cm− 1 (ν19b mode) does not overlap with any of the other bands.HPLC of Formula: 624-28-2