摘要:

Isothiazole 1,1‐dioxides – From Sweeter to Chiral Auxiliar in the Stereoselective SynthesisThis review gives a report of the last ten years on the new synthetic methods, reactions and biological applications of isothiazole 1,1‐dioxide derivatives. the formation of monocyclic and heterocyclic annelated isothiazole 1,1‐dioxides by oxidation of isothiazoles, cyclocondensation of sulfonamides and cycloaddition of isothiazol‐3(2H)‐one 1,1‐dioxides are discussed in more detail. Furthermore, the preparation of pharmacologically importantN‐substituted saccharines is reported. New saccharine‐derived chiral N‐enoyl‐andN‐acyl‐2,3‐dihydro‐1,2‐benzisothiazole 1,1‐dioxides serve as advantageous stereoface‐directing dienophile and dipolarophile auxiliaries in Diels‐Alder‐reactions and 1,3‐dipolar cycloadditions. Asymmetric alkylations, acylat

ISSN:0941-1216    

DOI:10.1002/prac.19973390102

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

Some Unusual Reactions of Disodium 2‐Oxo‐1,3‐dithiole‐4,5‐dithiolates with BiselectrophilesReaction of disodium 2‐oxo‐1,3‐dithiole‐4,5‐dithiolate(3)with dichloro‐maleic anhydride(4), Mucobromic acid(7)and its pseudoester9leads to the formation of the 1,3‐dithiolo[4,5‐b]‐1,4‐dithiins6, 8and10. 3condenses withcis‐3,5‐dibromo‐cyclopentene(15)to yield the tricyclic compounds16and17. 3is silylated by trimethylsilyltriflate(19)to give the unstable bis(trimethylsilyl)‐thioether20which reacts with aldehydes and ketones to furnish the 1,3‐d

ISSN:0941-1216    

DOI:10.1002/prac.19973390103

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractDehydration of 2‐(2‐arylethyl)‐2‐hydroxy‐4‐oxopentanoic acids1with hydrochloric acid/acetic acid, affords 3‐(2‐arylethyl)‐5‐hydroxy‐5‐methyl‐2(5H)‐furanones4. Compounds of type1and4represent suitable precursors for the formation of pyridazin‐3‐ones7as they smoothly react with hydrazine. A new series ofs‐triazolo[4,3‐b]pyridazin‐3‐ones12and tetrazolo[1,5‐b]pyridazines15are obtained from the 3‐chloropyridazines11upon treatment with semicarbazide and sodium azide, respectively. Reaction of11with phenyl‐ acetyl‐hydrazine provides 3‐benzyl‐6‐phenyl‐8‐(2‐phenyl‐ethyl)‐s‐triazolo[4,3‐b]pyridazine13viadehydrative cyclization of the intermediate14which was clarified to exhibit tautomeric equilibria between enol–hydrazine formAand keto–hydrazine formBby means of1H and13C NMR spectroscopy. Attempts to synthesize 3‐alloxy

ISSN:0941-1216    

DOI:10.1002/prac.19973390104

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

Interactions in Crystals. 96. Preparation and Structures of Salts [RnN⊕H…︁NRn][B⊖(C6H5)4] with Prototype Hydrogen Bridges N⊕H…︁NStraightforward crystallization of ammonium salts [RnN⊕H] X⊖added lithium tetraphenylborate, and amine RnN from acetone solution yields salts [RnN⊕H…︁NRn][B⊖(C6H5)4] with the (under the conditions) unprotonated anions and the cations with prototype hydrogen bridges N⊕H…︁N. The structures of both identically substituted RnN (methylamine, trimethylamine, quinuclidine, diazabicyclooctane, and pyridine) as well as two‐component cation species (quinuclidine…︁pyridine and diazabicyclooctane…︁pyridine) are reported and discussed. A Cambridge Structural Database search defines the area of charged N⊕H…︁N interactions which can be correlated with both pK BH +values and PM3 formation enthalpies. Additional information is provided by PM3 calculations based on the experimental structure coordinates. The charge distribution within the hydrogen bridges N⊕H…︁N varies considerably with the individual proton donors N+H and proton acceptors N: Positive charges are highest at protonated quinuclidine and diazabicycl

ISSN:0941-1216    

DOI:10.1002/prac.19973390105

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractCommercially available ω‐thioalkane sodium sulfonates could easily be added to mono‐, bi‐ and trivinylphosphines. The two‐phase system became homogeneous by stirring. The products(1–6, 11)were characterized as phosphinoethyl‐sulfonatoalkyl‐thioethers with an unexpected high water solubility and with defined P/S ratios from 1/2, 1/4 and 1/6. All thioetherphosphines were characterized by1H,13C and31P NMR spectroscopy, IR spectroscopy and elemental analysis. Addition occurs only at pH>7 and in the absence of strong electrophiles to avoid the formation of phosphonium compounds.L‐Cysteine ethyl ester(8)and 2‐aminoethanethiol(9)react exclusively at the thiol group. The first complexes with Pd(II), Rh(III) and Rh(I) show a participation of the thioether group i

ISSN:0941-1216    

DOI:10.1002/prac.19973390106

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

Determination of Trace Impurities in Tantalum Pentoxide by ICP‐AES and ICP‐MS after Trace‐Matrix‐SeparationA trace–matrix separation procedure based on anion exchange is presented. 500 mg Ta2O5are dissolved in hydrofluoric acid in a Teflon bomb. Ta is retained on the resin column in the form of different fluoro complexes. Most analytes pass the column as cations. Others, like Ti, Zr, Hf, V, Nb also form fluoro complexes. Based on a thorough investigation of the complex equilibria two selective elution procedures using 1M HCl or 0.5M HNO3+ 0.5M HF are developed. Both methods require a minimum of equipment and reagents, thus drastically reducing the risk of contaminations. The separation procedures are suitable for on‐line coupling with both ICP spectrometric techniques.More than 30 analytes can be determined including Ti, Zr, Hf, V, Nb, Mo, and W. Taking an aliquot of 100 mg Ta2O5detection limits are less than 1 μg for ICP‐AES or 10 ng for ICP‐MS for most elements. For example, 1.3 ng of Nb can be detected in 100 mg Ta2O5by ICP‐MS after separati

ISSN:0941-1216    

DOI:10.1002/prac.19973390107

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

Heterophanes with 1,3,5‐Triazines as Subunits and Thiol/Disulfide Redox SwitchThe synthesis and characterization of 5 new coronands2a–e, containing two 1,3,5‐triazine‐thiols as subunits and redox‐switch are described. Cryptands3a–ewith disulfide bridges were obtained by oxidation. Reduction of cryptands3a–eyields back the coronands2a–e. The different complexation properties of the macrocycles2a–dand3a–dtoward Tl(I), Ag(I) and Hg(II

ISSN:0941-1216    

DOI:10.1002/prac.19973390108

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractTwo primary amines, 1‐hexylamine2, 1‐dodecylamine19, one secondary amine, di‐1‐hexylamine18, and three tertiary amines,N,N‐dimethyl‐1‐hexylamine6,N,N‐dimethyl‐1‐butylamine3, andN,N‐dimethyl‐1‐dodecylamine22were each heated at 150 °C, 250 °C or 350 °C with 49% aqueous formic acid for varying periods of time. The aliphatic primary amines underwent easyN‐formylation and subsequent reduction to giveN‐methyl‐ andN,N‐dimethylalkylamines. Especially at higher temperatures, other reactions intervened including elimination of NH3to the corresponding alkenes followed by partial double bond isomerization. Tertiary amines were more reactive at higher temperatures undergoing hydrolysis and reductive cleavages to secondary and primary amines, which subsequently followed the reaction sequences seen for primary amines.This series of saturated amines showed none of the cleavage into smaller fragments that was observed in the reductive alkylation of pyridine and 4‐methylpyridine to a series ofN‐alkylpiperdines. This result reinforces the bis‐aza‐retro‐Aldol‐fragmentation mechanism postu

ISSN:0941-1216    

DOI:10.1002/prac.19973390109

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA new chiral olefin4was synthesized starting fromL‐aspartic acid. The structures of the intermediate oxazolidinones6and7were proven by X‐ray analysis to be diastereomers. It was shown that4is unreactive in Diels‐Alder reactions with cyclopentadiene and 1,3‐diphenyliso‐benzofuran because of its steric overloading (M.M. calculations) rather than by electronic effects (FMO by AM1 calc

ISSN:0941-1216    

DOI:10.1002/prac.19973390110

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

Synthesis and Reactivity oftert‐Butyl‐(2‐aryl‐3‐methyl‐but‐2‐yl) Peroxidestert‐Butyl‐(2‐aryl‐3‐methyl‐but‐2‐yl) peroxides(2a–d)were prepared fromt‐BuOOH and corresponding 2‐aryl‐methyl‐butan‐2‐ols(1a–d)(Ar:p‐MeOC6H4(a); Ph(b);p‐ClC6H4(c);m‐CF3C6H4(d)) and characterized by NMR, MS and elemental analysis.Kinetic data for the thermolysis of2a–din cumene as the solvent were determined at 110–140 °C and the products analyzed. The rate constants satisfy the Hammett equation with σ giving a ρ‐value of −0.73. Oxidation of2a–dat 80 °C gives the corresponding acetophenones4, epoxides6and hydroperoxides8. The products of the oxidation of2a–2dwere analysed after reduction of the reaction mixtures with LiAlH4. Relative reactivities of the tertiary CH bonds of peroxides2were determined by competitive oxidations

ISSN:0941-1216    

DOI:10.1002/prac.19973390111

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY