Molecules

77 KiB

Open AccessArticle

Thermal Rearrangement of Allyl Substituted Unsymmetric 4H-1,2,4-Triazoles to the Corresponding 1H-1,2,4-triazoles

by Kåre B. Jørgensen, Ragnhild B. Olsen and Per H.J. Carlsen

Molecules 2001, 6(5), 481-495; https://doi.org/10.3390/60500481 - 30 Apr 2001

Cited by 6 | Viewed by 8907

A series of neat 4-(2-alkenyl) substituted 5-methyl-3-phenyl-4H-1,2,4-triazoles were thermolyzed at 320 ^oC producing a rearrangement products, of which the regioisomeric 1- and 2-substituted triazoles were the main products. The group migrations were rationalized in terms of consecutive S_N2-type [...] Read more.

A series of neat 4-(2-alkenyl) substituted 5-methyl-3-phenyl-4H-1,2,4-triazoles were thermolyzed at 320 ^oC producing a rearrangement products, of which the regioisomeric 1- and 2-substituted triazoles were the main products. The group migrations were rationalized in terms of consecutive S_N2-type reactions. This mechanism was supported by a study of the alkylations of the triazoles which gave similar product mixtures. 4-(2-alkenyl) substituted 3-phenyl-4H-1,2,4-triazoles, on the other hand, gave predominantly elimination products. Full article

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90 KiB

Open AccessArticle

Synthesis of 2,4,6-Tris(4-N-isopropylamidinophenyl)pyrimidine trihydrochloride

by Miroslav Bajić and David W. Boykin

Molecules 2001, 6(5), 477-480; https://doi.org/10.3390/60500477 - 30 Apr 2001

Viewed by 7351

Abstract

The synthesis of 2,4,6-tris(4-N-isopropylamidinophenyl)pyrimidine from 1,3-di(4-bromophenyl)propen-3-one and 4-bromobenzamidine is reported. Full article

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30 KiB

Open AccessArticle

Generation and Cycloaddition of o-Quinodimethane in Aqueous Medium

by Lothar W. Bieber and Margarete F. Da Silva

Molecules 2001, 6(5), 472-476; https://doi.org/10.3390/60500472 - 30 Apr 2001

Cited by 10 | Viewed by 9439

Abstract

o-Quinodimethane can be generated from =α,α'-dihalo-o-xylenes using zinc in aqueous solution. In the presence of activated dienophiles cycloadducts can be obtained directly. Catalysis with tris-triphenylphosphine ruthenium(II) dichloride reduces side reactions such as reduction and polymerisation and improves the yield. This is the first [...] Read more.

o-Quinodimethane can be generated from =α,α'-dihalo-o-xylenes using zinc in aqueous solution. In the presence of activated dienophiles cycloadducts can be obtained directly. Catalysis with tris-triphenylphosphine ruthenium(II) dichloride reduces side reactions such as reduction and polymerisation and improves the yield. This is the first example of an organometallic cyclisation in aqueous medium using dihalo compounds. Full article

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24 KiB

Open AccessArticle

Facile and efficient synthesis of 3β-hydroxy-eupholanost-8-en-24-one

by N. El Aouad, A. Benharref and R. Gree

Molecules 2001, 6(5), 468-471; https://doi.org/10.3390/60500468 - 30 Apr 2001

Viewed by 7005

Abstract

The epoxidation of the natural product α-euphol followed by cleavage of the obtained epoxide with BF₃-etherate, provides 3β-hydroxy-eupholanost-8-en-24-one in satisfactory overall yield. Full article

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251 KiB

Open AccessArticle

Characterisation of Neuropeptide Y Receptor Subtypes by Synthetic NPY Analogues and by Anti-receptor Antibodies

by Christophe P. Eckard, Chiara Cabrele, Heike A. Wieland and Annette G. Beck-Sickinger

Molecules 2001, 6(5), 448-467; https://doi.org/10.3390/60500448 - 30 Apr 2001

Cited by 16 | Viewed by 9723

Abstract

Neuropeptide Y (NPY), a 36-mer neuromodulator, binds to the receptors Y₁, Y₂, Y₄ and Y₅ with nanomolar affinity. They all belong to the rhodopsin-like G-protein coupled, seven transmembrane helix spanning receptors. In this study, Ala-substituted and centrally [...] Read more.

Neuropeptide Y (NPY), a 36-mer neuromodulator, binds to the receptors Y₁, Y₂, Y₄ and Y₅ with nanomolar affinity. They all belong to the rhodopsin-like G-protein coupled, seven transmembrane helix spanning receptors. In this study, Ala-substituted and centrally truncated NPY analogues were compared with respect to affinity to the Yreceptors. Furthermore, antibodies against the second (E2) and the third (E3) extracellular loop of NPY Y₁-, Y₂- and Y₅-receptor subtypes were raised and affinity to intact cells was tested by immunofluorescence assays. Both methods were applied in order to receive subtype selective tools and to characterise ligand binding. The analogues [A¹³]-pNPY and [A²⁷]-pNPY showed subtype selectivity for the Y₂-receptor. Sera against the E2 loop of the Y₁-receptor and against the E2 loop of the Y₂-receptor were subtype selective. Two antibodies against the Y₅ E2 and E3 loop recognised the Y₅- and Y₂-receptor subtypes. In combination, these sera are able to distinguish between the Y₁-, Y₂-, and Y₅-receptor subtypes. The analogues and antibodies represent valuable tools to distinguish NPY receptors on membranes and intact cells. Full article

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69 KiB

Open AccessArticle

Facile and Fast Pinacol Rearrangement by AlCl₃ in the Solid State

by Parviz Rashidi-Ranjbar and Ebrahim Kianmehr

Molecules 2001, 6(5), 442-447; https://doi.org/10.3390/60500442 - 30 Apr 2001

Cited by 11 | Viewed by 10059

Abstract

A facile and efficient synthetic procedure for effecting the pinacol rearrangement catalyzed by AlCl₃ in the absence of solvent is developed. The rearrangement product is obtained at room temperature in a few minutes and in almost quantitative yield. Benzylic pinacols rearrange under [...] Read more.

A facile and efficient synthetic procedure for effecting the pinacol rearrangement catalyzed by AlCl₃ in the absence of solvent is developed. The rearrangement product is obtained at room temperature in a few minutes and in almost quantitative yield. Benzylic pinacols rearrange under these conditions, while aliphatic pinacols do not react. Full article

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177 KiB

Open AccessArticle

Molecular and Crystal Structures of Three Berberine Derivatives

by Stanislav Man, Milan Potáček, Marek Nečas, Zdirad Žák and Jiří Dostál

Molecules 2001, 6(5), 433-441; https://doi.org/10.3390/60500433 - 30 Apr 2001

Cited by 20 | Viewed by 8606

Abstract

Berberine azide, berberine thiocyanate, and 8-cyano-8H-berberine were prepared from berberine chloride, a quaternary protoberberine alkaloid. The molecular and crystal structures of all compounds are reported and discussed. Full article

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93 KiB

Open AccessArticle

On the Additions of Lithium Methyl p-Tolyl Sulfoxide to N-(PMP)Arylaldimines

by Cristina Zucca, Pierfrancesco Bravo, Eleonora Corradi, Stefano V. Meille, Alessandro Volonterio and Matteo Zanda

Molecules 2001, 6(5), 424-432; https://doi.org/10.3390/60500424 - 30 Apr 2001

Cited by 4 | Viewed by 9087

Abstract

The results presented in this paper confirm that the stereochemical outcome of the reversible additions of lithium (R)-methyl p-tolyl sulfoxide to N-arylidene-p-anisidines (NPMP imines) depends on: (a) the reaction conditions used and (b) the electronic properties of the arylidene moiety on the starting [...] Read more.

The results presented in this paper confirm that the stereochemical outcome of the reversible additions of lithium (R)-methyl p-tolyl sulfoxide to N-arylidene-p-anisidines (NPMP imines) depends on: (a) the reaction conditions used and (b) the electronic properties of the arylidene moiety on the starting imine. In particular, we show that under kinetic control (-70 °C) the additions involving electron-rich N-arylidene groups occur with very high stereocontrol in favor of the (2S,RS)-diastereomers, whereas an electron-deficient group favors the opposite stereochemical outcome. Based on the observations above, a mechanistic hypothesis is proposed. Full article

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Molecules, Volume 6, Issue 5 (May 2001) – 8 articles , Pages 424-495

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