1,721,120 research outputs found
Synthesis of functionalised furans and pyrroles through annulation reactions of 4-pentynones
No full textA new approach to 4-pentynones through palladium-catalysed coupling reaction of the ready available 2-propynyl ketones with aryl iodides and/or vinyl triflates is proposed. Annulation reactions of both 2-propynyl ketones and 4-pentynones gave functionalised furans using potassium tert-butoxide in DMF and functionalised pyrroles in the presence of benzylamine or ammonia, respectively in good to high yields. The methodology has been extended to the preparation of 17 beta-hydroxyandrost-4-en[3,2-b](5-methyl)furan and to 17 beta-hydroxyandrost-4-en[3.2-b](1-benzyl-5-methyl)pyrrole. A different reaction pattern was observed when the 4-pentynones were treated with sodium methoxide in MeOH. The influence of the reaction medium on the outcome of the annulation reaction in the case of one 2-pentyn-1,6-dione (heteroannulation vs. carbocyclization) is also shown. (C) 1998 Published by Elsevier Science Ltd. Ail rights reserved
Molecular structure and benzene ring deformation of three ethynylbenzenes from gas-phase electron diffraction and quantum chemical calculations
No full textThe molecular structures of ethynylbenzene and s-triethynylbenzene have been accurately determined by
gas-phase electron diffraction and ab initio/DFT MO calculations and are compared to that of p-diethynylbenzene
from a previous study [Domenicano, A.; Arcadi, A.; Ramondo, F.; Campanelli, A. R.;
Portalone, G.; Schultz, G.; Hargittai, I. J. Phys. Chem. 1996, 100, 14625]. Although the equilibrium structures
of the three molecules have C2v, D3h, and D2h symmetry, respectively, the corresponding average structures
in the gaseous phase are best described by nonplanar models of Cs, C3v, and C2v symmetry, respectively. The
lowering of symmetry is due to the large-amplitude motions of the substituents out of the plane of the benzene
ring. The use of nonplanar models in the electron diffraction analysis yields ring angles consistent with those
from MO calculations. The molecular structure of ethynylbenzene reported from microwave spectroscopy
studies is shown to be inaccurate in the ipso region of the benzene ring. The variations of the ring C-C
bonds and C-C-C angles in p-diethynylbenzene and s-triethynylbenzene are well interpreted as arising from
the superposition of independent effects from each substituent. In particular, experiments and calculations
consistently show that the mean length of the ring C-C bonds increases by about 0.002 Å per ethynyl group.
MO calculations at different levels of theory indicate that though the length of the C≡C bond of the ethynyl
group is unaffected by the pattern of substitution, the Cipso-Cethynyl bonds in p-diethynylbenzene are 0.001-
0.002 Å shorter than the corresponding bonds in ethynylbenzene and s-triethynylbenzene. This small effect
is attributed to conjugation of the two substituents through the benzene ring. Comparison of experimental
and MO results shows that the differences between the lengths of the Cipso-Cethynyl and Cipso-Cortho bonds in
the three molecules, 0.023-0.027 Å, are correctly computed at the MP2 and B3LYP levels of theory but are
overestimated by a factor of 2 when calculated at the HF level
Synthesis of functionalised quinolines through tandem addition/annulation reactions of beta-(2-aminophenyl)-alpha,beta-ynones
No full textbeta-(2-aminophenyl)-alpha,beta-ynones can quickly give functionalized 2,4-disubstituted quinolines through tandem nucleophic addition/annulations reactions. Acid-catalysed cyclization of beta-(2-aminophenyl)-alpha,beta-ynones can also occur. The easy entry into 4-iodo-2-substituted-quinolines prompted the development of a one pot procedure for synthesis of 2,4-disubstituted quinolines by further elaboration by means of palladium-catalysed reactions. The exposure to basic conditions of one beta-(2-malonylamidophenyl)-alpha,beta-ynone led to a fused quinolone derivative through intramolecular Michael addition /tautomerisation/transesterification cascade reactions. Fused polycyclic quinolines can be viewed as occurring through a tandem concerted Diels-Alder/annulation reactions of beta-(2-aminophenyl)-alpha,beta-ynones with enamines, azides and nitrile oxides. (C) 1999 Elsevier Science Ltd. Ail rights reserved
REAZIONI TANDEM DI CICLOADDIZIONE/ANNULAZIONE DI beta-(2-AMMINOFENIL)-alfa,beta-INONI
No full textIl nucleo chinolinico è presente in diversi composti di origine naturale ed in alcune sostanze farmacologicamente attive quali antiasma, inibitori delle lipoossigenasi ed in alcuni nuovi derivati antiinfiammatori. Per questo motivo lo sviluppo di nuovi metodi sintetici per il nucleo chinolinico continua ad essere una interessante area di ricerca.
In questa comunicazione intendiamo riportare alcuni risultati preliminari di un lavoro di sintesi che, utilizzando come substrati alfa,beta-inoni, attraverso reazioni tandem di cicloaddizione e annulazione permette di ottenere anelli chinolinici condensati
Base promoted reactions of 4-pentynones
No full textDifferent substituted furans are synthesized by cyclization of 4-pentynones using potassium tert-butoxide in DMF. A different reaction pattern is observed when the same componds were treated with sodium methoxide in MeOH. A new approach to 2-propargyl-carbonyl compounds is also proposed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Novel intramolecular cyclization of N-alkynyl heterocycles containing proximate nucleophiles
No full textIntramolecular cyclization of 2-acyl-1-propargyl-1H-indoles in the presence of ammonia provides an easy entry to pyrazino[1,2-a]indole nucleu
Concise synthesis of fused polycyclic quinolines
No full textβ-(2-Aminophenyl)-α,β-ynones react with enamines of cyclic ketones by domino [2+2]cycloaddition/annelation reaction giving rise to bicyclo[4.2.0]-octane[7,8-c]-2-aryl quinolines or to c-fused quinolines. The reactivity of ynones towards acyclic enamines and thermal rearrangement of tetracyclic to the corresponding tricyclic derivatives are also described
SINTESI DI PIRAZINO[1,2-a]INDOLI TRAMITE REAZIONI DI CICLIZZAZIONE INTRAMOLECOLARE DI 2-ACIL-1-PROPARGIL INDOLI
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