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Applications of Computational and NMR Methodologies to the Study of Homoallylic Alcohols Diastereomers

1
Instituto de Química del Sur (INQUISUR-CONICET), Departamento de Química, Universidad Nacional del Sur, Avenida Alem 1253, B8000CPB Bahía Blanca, Argentina
2
Unidad de Resonancia Magnética, Universidad de Alicante (UA), Carretera de San Vicente del Raspeig s/n, 03690 San Vicente del Raspeig, Alicante, España
*
Authors to whom correspondence should be addressed.
Presented at the 22nd International Electronic Conference on Synthetic Organic Chemistry, 15 November– 15 December 2018; Available Online: https://sciforum.net/conference/ecsoc-22.
Proceedings 2019, 9(1), 12; https://doi.org/10.3390/ecsoc-22-05782
Published: 14 November 2018
PDF [804 KB, uploaded 18 March 2019]
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Abstract

Through reducing the system InCl3-Li-DTBB(cat.) in THF at room temperature and in the absence of any additives or anti-caking ligand, we have synthesized indium nanoparticles (InNPs) of about 4 nm. The catalyst was employed in the allylation of carbonyl compounds, giving excellent yields of the corresponding homoallylic alcohols. We have established that the reaction products come from a γ-coupling via a six members cyclic transition state, type Zimmerman–Traxler. Relative to the selectivity, the allylation with crotyl bromide of ortho substituted benzaldehydes (e.g., o-NO2, o-OMe, o-Cl, o-CF3) showed syn selectivity. With the aim to improve the mentioned selectivity, we synthetized o-iPrO-benzaldehyde, and evaluated the reaction with crotyl bromide and InNPs. The homoallylic alcohol 1-(2-isopropoxyphenyl)-2-methylbut-3-en-1-ol was obtained almost quantitatively after 1h as a mixture of the syn- and anti- isomers. The relationship observed by 1H-RMN was 75:25, but we did not know if the syn-isomer was the dominant because the product has not been reported in the scientific literature. Based on this, and in order to determinate which 1H-NMR signals correspond to each isomer, we started computational theoretical and NMR studies. The initial conformational analysis was performed using the semiempirical PM3 method, then we work with the B3LYP functional, applying the 6-31+G* basis set and the solvent effect (chloroform) was evaluated with the PCM model as implemented in Gaussian09. So, we found thirteen low-energy conformations for the syn-diastereomer and six low-energy conformations for the anti-diastereomer. On the other hand, we have carried out NMR experiments such as 1H, 13C, HSQC, to assign the signals of each diastereomer; and experiments such as NOESY, selective NOE, JRes, homo- and hetero-nuclear J-coupled and J-decoupling, to be able to measure coupling constants and establish the structure of each diastereomer.
Keywords: indium nanoparticles; DFT; NMR indium nanoparticles; DFT; NMR
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Dorn, V.; Martínez, E.L.; Radivoy, G. Applications of Computational and NMR Methodologies to the Study of Homoallylic Alcohols Diastereomers. Proceedings 2019, 9, 12.

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