100017-18-3Relevant articles and documents
Absolute configurations of melanoxadin, MR-93A, melanoxazal, and MR-93B
He, Tian-Jun,Zhu, Shijun,Lu, Xiao-Wei,Wu, Yikang,Li, Yan
, p. 647 - 654 (2015/01/30)
Fungal metabolites melanoxadin, MR-93A, melanoxazal, and MR-93B were synthesized with the key stereogenic centers derived from commercially available chiral building blocks. The optically active synthetic products with well-defined absolute configurations provided authentic samples for the stereoisomers of these oxazole-containing natural products and thus allowed for unambiguous assignments of their relative and absolute configurations. The large discrepancies in the optical rotations between the natural and the pure synthetic samples are discussed. Some errors in the previously reported NMR signal assignments are also corrected.
Optically Active Alcohols from 1,3-Dioxan-4-ones. A Practical Version of Enantioselective Synthesis with Nucleophilic Substitution at Acetal Centers
Seebach, Dieter,Imwinkelried, Rene,Stucky, Gerhard
, p. 448 - 464 (2007/10/02)
Secondary alcohols in enantiomeric excesses above 90percent are accessible from 2-substituted 6-methyl-1,3-dioxan-4-ones.The dioxanones are prepared from aldehydes and readily available (R)- or (S)-3-hydroxybutanoic acid.Treatment of the dioxanones with silyl nuclophiles or triisopropoxy(methyl)titanium in the presence of yields the corresponding 3-alkoxy acids in diastereoselectivities >/= 95percent.The 'chiral auxiliary" is removed from the alkoxy acids by treatment with LiN(i-Pr)2 to give the secondary alcohols with >/= 90percent ee. cis/trans-Mixtures (9:1) of the dioxanones furnish products of the same configurational purity as those obtained from pure cis-isomers.In comparison with other variants of enantioselective syntheses with nucleophilic substitution at acetal centers, the following advantages of the dioxanone method are noteworthy: i) (R)- and (S)-3-hydroxybutanoic acids are both readily available; ii) reactions are not sensitive to changes in conditions; iii) the 'chiral auxiliary' is removed simply by base elimination, no oxidation is required; iv) no chromatographic purification steps are necessary.The overall reaction described here is an enantioselective nucleophilic addition to aldehydes with concomitant dehydration of enantiomerically pure 3-hydroxybutanoic to crotonic acid.
123. 1,3-Dioxanone Derivatives from β-Hydroxy-carboxylic Acids and Pivalaldehyde. Versatile Buiding Blocks for Syntheses of Enantiomerically Pure Compounds. A Chiral Acetoacetic Acid Derivative
Seebach, Dieter,Zimmermann, Juerg
, p. 1147 - 1152 (2007/10/02)
(R)-3-Hydroxybutyric acid (from the biopolymer PHB) and pivalaldehyde give the crystalline cis- or (R,R)-2-(tert-butyl)-6-methyl-1,3-dioxan-4-one (1a), the enolate of which is stable at low temperature in THF solution and can be alkylated diastereoselectively (->3, 4, 5, and 7).Phenylselenation and subsequent elimination give an enantiomerically pure enol acetal 10 of aceto-acetic acid.Some reactions of 10 have been carried out, such as Michael addition (->11), alkylation on the CH3 substituent (->13), hydrogenation of the C=C bond (->1a) and photochemical cycloaddition (->16).The overall reactions are substitutions on the one sterogenic center of the starting β-hydroxy acid without racemization and without using a chiral auxiliary.