Synthesis of novel O-acylated-D-ribono-1,5-lactones and structural assignment supported by conventional NOESY-NMR and x-ray analysis
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A practical method for the structural assignment of 3,4-O-benzylidene-D-ribono-1,5-lactones and analogues using conventional NMR techniques and NOESY measurements in solution is described. 2-O-Acyl-3,4-O-benzylidene-D-ribono-1,5-lactones were prepared in good yields by acylation of Zinner’s lactone with acyl chlorides under mildly basic conditions. Structural determination of 2-O-(4-nitrobenzoyl)-3,4-O-benzylidene-D-ribono-1,5-lactone was achieved by single crystal x-ray diffraction, which supports the results based on spectroscopic data.At 40°(undissociated) 2-naphthol and p-nitrophenol are, respectively, 1·8 and 1·1 times more reactive towards acetyl chloride in acetic acid than are their thiol analogues. This result supports our predictions about the acylation of thiols. The thiols appear more easily acylated than would be predicted from their thermodynamic acidities.
Thiol
Benzoyl chloride
Acetyl chloride
Acyl chloride
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Al(2)O(3) brings about a rapid acylation of a range of alcohols and amines with acid chlorides and acid anhydrides, respectively. Amines are easily Boc- and Cbz-protected on reaction with Boc-anhydride and Cbz-Cl, respectively. The acylation of phenols is slow enough to allow chemoselective acylation of alcohols and amines in the presence of phenols.
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Three new guaianolides, 10α-hydroxy-3-oxoguaia-4(15),11(13)-dieno-12,6α-lactone (1), 10α-hydroxy-3-oxo-4βH-guaia-11(13)-eno-12,6α-lactone (2), and 10α-hydroxy-3-oxoguaia-4,11(13)-dieno-12,6α-lactone (3), named chinensiolides A, B, and C were isolated from the whole plant of Siyekucai (Ixeris chinensis). The structures were determined by HREIMS, UV, IR, and one- and two-dimensional NMR techniques (1H and 13C NMR, COSY, HMQC, HMBC, and NOE difference and NOESY experiments). Compounds 1 and 2 were indicated to be a mixture of flexible conformers by analyses of their 1D NOE and NOESY spectra as well as the temperature dependence of their 1H and 13C NMR spectra. Chinensiolide B (2) was transformed to chinensiolide C (3) in a three-step conversion.
Sesquiterpene lactone
Conformational isomerism
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Succinylation
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Quinolone derivatives have been used as antibacterial agents. In this work, the competitive C-and O-acylation reaction of 3,4-dichloroacetophenone, as a model study for the synthesis of quinolone intermediate, is studied. The effects of various bases, solvents and the leaving groups of acylating agents on the ratio of C-versus O-acylation of 3,4-dichloroacetophenone are elucidated by means of employing ethylchloroformate, ethylphenylcarbonate and diethylcarbonate as acylating agents. In aprotic solvents, C-acylation reactions occur more predominantly as the size of metal ions composing bases becomes smaller. Regarding the effects of leaving groups, it is shown that C-acylation product is increased as the ability of leaving groups of acylating agents decreases. The ratio of C/O-acylation is also observed to be increased as the polarity of solvents decreases.
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The acylation courses of 5-bromo and 5,7-dibromo derivatives of benzoxazolin-2--one (BO) and isomeric 3-hydroxy-1,2-benzisoxazoles (BIO) with acetic anhydride, benzoyl chlorides and alkyl chloroformates were investigated. In view of principal course of N-acylation in BO-and O-acylation in BIO-group some of the newly obtained compounds, namely 5,7-Br2-2-(o-chlorobenzoyloxy)-BO (5a) and N-alkoxycarbonyl BIO (22a--27a) make the exceptions. Compounds 25a and 26a were found to possess relatively the most intensive depressant action on the CNS.
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3 (C) -Acylation of 3-unsubstituted tetramic acids with carboxylic acid has been achieved by two sequential reactions in one flask : (1) 4 (O) -acylation in the presence of DCC and a catalytic amount of DMAP, and (2) 4 (O) →3 (C) acyl-migration promoted by adding Et3N.
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A thorough study of the synthesis of 2,4-diacylpyrroles by direct acylation of pyrrole and 2- and 3-acylpyrroles is reported. Among these, Friedel–Crafts acylation of 3-acylpyrroles is the most general and advantageous method because it utilises easily accessible starting materials. In addition it is always regiospecific and readily provides 2,4-diacylpyrroles containing identical or different acyl groups in very high yields (81–100%) under mild conditions. Alternative procedures concern the synthesis of precursors of 2,4-diacylpyrroles containing one or two acyl groups masked by a 1,3-benzodithiolyl or 1,3-benzoxathiolyl group and subsequent hydrolysis with HgO–35% aq. HBF4Me2SO. Overall yields are always good (52–60%). Indirect acylation constitutes a secure complement to direct acylation when it is necessary to operate in the presence of protected acyl groups.
Pyrrole
Acyl group
Complement
Protecting group
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