Origin of diastereoselectivity in the synthesis of chiral bicyclic lactams: pi-facial selective attack of singlet oxygen induced by hindered internal rotation

Date

2007-07-05

Author

Catak, Saron
Celik, Hasan
Demir, Ayhan Sıtkı
Aviyente, Viktorya

Metadata

Show full item record

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Item Usage Stats

185
views

0
downloads

Previously reported experimental results indicate that photooxygenation of homochiral N-(hydroxyalkyl)-2-methylpyrroles with singlet oxygen yields transrather than cis-bicyclic lactams as the major product. In this study, the origin of selectivity in this reaction has been investigated with computational methods. Relative stabilities of homochiral N-(hydroxyalkyl)-2-methylpyrrole conformers and their effect on pi-facial selectivity of O-1(2) were extensively studied. Stepwise and concerted reaction mechanisms, starting from the endoperoxide intermediates, were proposed and modeled in vacuum using the UB3LYP method with the 6-31+G** basis set. Solvent calculations were carried out in CH2Cl2, by means of the integral equation formalism-polarizable continuum model (IEF-PCM) at the UB3LYP/6-31+G** level of theory. Free energies of activation leading to both diastereomers were analyzed in an effort to explain the stereoselectivity and product distribution. Steric interactions among the pyrrole substituents were shown to lead to a rotational barrier higher than 10 kcal/mol. Hence, hindered internal rotation is suggested to cause one pyrrole conformer to be substantially overpopulated. This in turn has a major effect on pi-facial selectivity of O-1(2), thereby favoring one endoperoxide over the other and leading to the diastereoselective synthesis of trans-pyrrolooxazolones. The importance of hindered internal rotors, for an accurate calculation of the frequency factors of a chemical reaction, has already been mentioned in the literature many times; however, in this work hindered internal rotors also seem to dictate the diastereoselective outcome of the reaction.

Subject Keywords

Physical and Theoretical Chemistry

URI

https://hdl.handle.net/11511/56934

Journal

JOURNAL OF PHYSICAL CHEMISTRY A

DOI

https://doi.org/10.1021/jp071608y

Collections

Department of Chemistry, Article

Suggestions

OpenMETU
Core

The role of antiferromagnetic exchange interactions in dinuclear Cr(III) dithiocarbamates and a stepwise behavior of magnetic moment AYTEKİN, ÖZLEM; Bayri, A. (Pleiades Publishing Ltd, 2012-12-01) In this study the role of the antiferromagnetic interactions in recently synthesized dinuclear Cr(III) complex has been investigated. Since there was not enough structural information for the characterization of the synthesis, we claim that there should be antiferromagnetic interactions between the dinuclear Fe(III) ions, if the proposed structure is the real structure. A new experiment is proposed to test the predictions of this theoretical investigation.
Structure sensitivity of selective CO oxidation over Pt/gamma-Al2O3 Atalik, B.; Üner, Deniz (Elsevier BV, 2006-07-25) In this study, the effect of particle size on the reaction rate and selectivity of preferential oxidation of CO (PROX) reaction was investigated on 2 wt% Pt/-Al2O3 catalysts prepared by an incipient wetness technique. The particle size of the catalysts was modified by calcination temperature and duration. CO oxidation and preferential CO oxidation reaction were studied on these catalysts at lambda = 2 (P-O2/P-CO) = 1. The CO oxidation reaction activation energy decreased with increasing particle size, consi...
Novel ruthenium(II) and iridium(III) BODIPY dyes: insights into their application in photodynamic therapy in vitro Aksakal, Nuray Esra; TANRIVERDİ EÇİK, ESRA; Kazan, Hasan Hueseyin; Ciftci, Goenuel Yenilmez; YÜKSEL, FATMA (Royal Society of Chemistry (RSC), 2019-08-01) Organic-metal complexes are promising molecules for use in photodynamic therapy (PDT). The aim of this study was to investigate in vitro effects of novel Ru(ii) and Ir(iii) BODIPY complexes for PDT. These hybrid organic-metal molecules (Ru-BD and Ir-BD) have been synthesized via reactions of a BODIPY precursor (BD) with a phenanthroline unit bearing Ru(ii) (3) and novel Ir(iii) (4) compounds. The crystal structures of the new distyryl BODIPY (BD) and Ru(ii) complex (3) are also reported. The photophysical a...
OPTIMIZATION OF THE VOLUMETRIC HYDROGEN CHEMISORPTION TECHNIQUE FOR DISPERSIONS OF RU/SIO2 CATALYSTS Üner, Deniz; KING, TS (Elsevier BV, 1995-09-15) Metal dispersions of silica-supported ruthenium catalysts determined by the standard volumetric chemisorption technique were found to be inaccurate due to irreversible spillover of hydrogen to the support. Direct evidence was obtained via in situ H-1 NMR for an irreversibly bound component of the hydrogen that migrated from the metal to the support on a time scale of tens of minutes or longer at room temperature. It was also shown in this work that hydrogen saturated the surface of the metal particles on a ...
Regioselective Synthesis of Benzo[h][1,6]- naphthyridines and Chromenopyrazinones through Alkyne Cyclization Hoplamaz, Emre; KESKİN, SELBİ; Balcı, Metin (Wiley, 2017-03-17) A regioselective approach to the synthesis of benzo[h][1,6]-naphthyridine and chromenopyrazinone derivatives was developed. The synthetic route to benzo[h][1,6]naphthyridines involves the N-propargylation of aromatic aminobenzaldehydes, followed by reaction with propargylamine in the presence of DBU (1,8-diazabicyclo[5.4.0] undec-7ene). For the synthesis of chromenopyrazine and chromeno-pyrazinone derivatives, the acetonitrile group was introduced to salicylaldehyde derivatives, and a DBU-promoted cyclizati...

Citation Formats

S. Catak, H. Celik, A. S. Demir, and V. Aviyente, “Origin of diastereoselectivity in the synthesis of chiral bicyclic lactams: pi-facial selective attack of singlet oxygen induced by hindered internal rotation,” JOURNAL OF PHYSICAL CHEMISTRY A, pp. 5855–5863, 2007, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/56934.