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p. 845-851
Received: 3 September 2001; in revised form: 15 October 2001 / Accepted: 16 October 2001 / Published: 31 October 2001
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| Download PDF Full-text (81 KB) Abstract: We report that a subtle balance of carbanion reactivity, leaving group activation, and pKa of the catalyst is required for efficient self-condensation of thiomalonates to thioacetoacetates in up to 71% yield under “biomimetic” conditions originally proposed by Kobuke and Yoshida (Tetrahedron Lett . 1978, 19, 367).
p. 852-868
Received: 27 April 2001; in revised form: 11 October 2001 / Accepted: 18 October 2001 / Published: 31 October 2001
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| Download PDF Full-text (95 KB) Abstract: The Baylis-Hillman reactions of various aryl aldehydes with methyl vinyl ketone at temperatures below -20oC using Lewis acids such as titanium (IV) chloride, boron (III) chloride or zirconium (IV) chloride in the presence of a catalytic amount of selected amines used as a Lewis bases afford the chlorinated compounds 1 as the major product in very high yields. Acrylonitrile can also undergo the same reaction to give the corresponding chlorinated product in moderate yield. A plausible reaction mechanism is proposed. However, if the reaction was carried out at room temperature (ca. 20oC), then the Z-configuration of the elimination product 3, derived from 1, was formed as the major product.
p. 869-874
Received: 27 September 2001; in revised form: 11 October 2001 / Accepted: 12 October 2001 / Published: 31 October 2001
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| Download PDF Full-text (33 KB) Abstract: Ten representative (dichloroiodo)arenes, ArICl2 , were prepared from the corresponding arenes and diiodine in variable anhydrous mixtures, ArH/I2 /CrO3 /AcOH/Ac2 O/conc. H2 SO4 , followed by the addition of conc. hydrochloric acid, used as the source of chlorine; ArICl2 are useful in organic synthesis as mild and selective chlorinating and/or oxidizing agents.
p. 875-880
Received: 27 September 2001; in revised form: 11 October 2001 / Accepted: 12 October 2001 / Published: 31 October 2001
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| Download PDF Full-text (35 KB) Abstract: This paper reports a one-pot synthesis of the title bromides from both activated and deactivated iodoarenes which are first oxidized with anhydrous NaBO3 ·H2 O/Ac2 O/conc.H2 SO4 liquid mixtures, then coupled in situ with benzene and activated arenes and, finally, precipitated out with a KBr solution; this method is easy, cheap, safe and fairly effective.
p. 881-891
Received: 27 September 2001; in revised form: 11 October 2001 / Accepted: 12 October 2001 / Published: 31 October 2001
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| Download PDF Full-text (103 KB) Abstract: - Easy, safe, and effective novel methods for preparing either (diacetoxyiodo)-arenes, ArI(OAc)2 , or iodylarenes, ArIO2 , from the corresponding iodoarenes, ArI, using sodium periodate as the oxidant are presented in this paper. In order to obtain 2- and 4-iodylbenzoic acids, the respective sodium salts of 2- and 4-iodobenzoic acids should be used as the starting substrates, because mixtures containing the corresponding iodosyl derivatives as the main products along with the intended iodyl compounds are produced from the free parent acids.
p. 892-899
Received: 26 February 2001; in revised form: 15 October 2001 / Accepted: 18 October 2001 / Published: 31 October 2001
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| Download PDF Full-text (119 KB) Abstract: A strategy to create the –CH(NR2 )CO- moiety from captodative formyl enamines was successfully applied to the synthesis of tertiary α-amino esters.
p. 900-908
Received: 9 August 2001; in revised form: 25 September 2001 / Accepted: 22 October 2001 / Published: 31 October 2001
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| Download PDF Full-text (81 KB) Abstract: The synthetic utility of potassium dichromate in the presence of Lewis acids under solid phase conditions is described. This reagent efficiently oxidizes alcohols, acyloins, oximes and semicarbazones to their corresponding carbonyl compounds, while trimethylsilyl and tetrahydropyranyl ethers, ethylene acetals and ketals undergo oxidative deprotection to produce carbonyl compounds efficiently.
p. 909-914
Received: 19 June 2001; in revised form: 24 September 2001 / Accepted: 22 October 2001 / Published: 31 October 2001
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| Download PDF Full-text (172 KB) Abstract: The asymmetrical tripodal tetraamine ligand N[(CH2 )3 NH2 ]2 [(CH2 )2 NH2 ] (ppe) was condensed with 2-acetylpyridine in the presence of nickel(II) ion. In ethanolwater solution the reaction stops after the first stage of condensation, and a new nickel(II) complex of an acyclic pentadentate (N5 ) mono Schiff base ligand was obtained. X-ray structure analysis of the resulting complex, [Ni(ppe-py)(H2 O)](ClO4 )2 , indicates that condensation with 2-acetylpyridine is at the propylene chain of ppe. The geometry around the nickel ion is distorted octahedral in which the sixth co-ordination group is a solvent molecule.
p. 915-926
Received: 15 July 2001 / Accepted: 24 October 2001 / Published: 31 October 2001
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| Download PDF Full-text (59 KB) Abstract: A new effective algorithm for handling of geometry at chiral centers for the processing of stereochemical structures during their unambiguous registration in databases was designed, programmed and implemented. The chemical and mathematical reasoning behind the algorithm are discussed in detail. Its advantages- in comparison to the methods used so far - are illustrated for the manual as well as for the computerassisted assignment of stereodescriptors based on the CIP ranking procedure.
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