Neu dargestellt wurden Rb2HgF4 und Cs2HgF4, beide farblos. Nach Einkristalluntersuchungen kristallisieren beide tetragonal im K2NiF4‐Typ in der Raumgruppe I 4/mmm‐D4h17 (Nr. 139), mit a = 455,6 pm, c = 1375,7 pm, Z = 2 für Rb2HgF4 und a = 462,5 pm, c = 1451,8 pm, Z = 2 für Cs2HgF4. Einkristalluntersuchungen an Hg2F2, hellgelb, bestätigen die Elementarzelle [1] mit a = 367,00(4) pm, c = 1 090,1(2) pm, Z = 2 in der Raumgruppe I 4/mmm‐D4h17 (Nr. 139).
(R)‐ and (S)‐2,3‐dihydroxy‐3‐methylbutyl p‐toluenesulfonate, used as building blocks for vitamine D3 metabolites and carotenoids, respectively, were resynthesized since differing melting points and optical rotations are reported in the literature. The given data of the (S)‐enantiomer could be corrected. A method for the determination of the enantiomeric purity was elaborated using the influence of a chiral lanthanide shift reagent on the 1H‐n.m.r. spectra of these compounds. By this way it was shown that both compounds exhibit an enantiomeric excess of more than 94%. The (S)‐enantiomer was synthesized according to an improved synthetic scheme starting from L‐serine.
Homochiral 3‐alkylated (2R,3R)‐ and (2R,3S)‐2,3‐dihydroxyalkyl p‐toluenesulfonates (9 and 10) are essential building blocks for vitamin D3 metabolites with a modified side chain. Nine of these compounds have been prepared starting from (R)‐2,3‐O‐cyclohexylideneglyceraldehyde (1) by addition of alkylmagnesium halides, Jones oxidation of the obtained diastereomeric alcohols 2 and 3 to the corresponding ketones 4, and a second addition of alkylmagnesium halides, followed by hydrolytic removal of the cyclohexylidene group and selective tosylation. The opposite diastereoselectivity of the two Grignard reactions is discussed.
Oxidative cleavage of 1,2:5,6‐di‐0‐cyclohexylidene‐D‐mannitol (2) with lead (IV) acetate yields (R)‐2,3‐0‐cyclohexylideneglyceraldehyde, which was transformed by oxidation and esterification into methyl 2,3‐0‐cyclohexylideneglycerate. Grignard reaction with various alkylmagnesium halides followed by acid‐catalyzed removal of the acetal group and reaction with p‐toluenesulfonyl chloride in pyridine furnished the title compounds (8a–d) in good chemical overall yield and high enantiomeric purity. The compounds were prepared as intermediates for the synthesis of a series of steroids with a modified side chain.
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