Stereochemical study of iminodihydrofurans based on experimental measurements and SOPPA calculations of ¹³C¹³C spin–spin coupling constants

Abstract

Configurational assignment and conformational analysis of a series of iminodihydrofurans obtained from cyanoacetylenic alcohols were performed on the basis of experimental measurements and high-level ab initio calculations of their (13)C-(13)C spin-spin coupling constants. The title compounds were shown to form and exist in solution as the individual Z isomers, adopting the orthogonal orientation of the amino, alkylamino and dialkylamino groups and the s-trans orientation of the CONH(2) group at the C(4) position of the 2,5-dihydro-2-iminofuran moiety.

Torsion angle relationship of the 17O NMR chemical shift in α,β‐unsaturated carbonyl compounds

“…[30] is also present in these compounds. [30] therefore, the experimental determination of the 1 J(C,C) might constitute a further proof of the conformational preferences of these compounds inferred with the present and past studies.…”

“…To check whether such an approach might also be useful on the benchmark molecules analyzed in the present work, we calculated the values of the mentioned coupling constants in the stable conformations, and it was found that the stereochemical behavior of 1 J(C,C) observed in Ref. [30] is also present in these compounds. [30] therefore, the experimental determination of the 1 J(C,C) might constitute a further proof of the conformational preferences of these compounds inferred with the present and past studies.…”

“…Also, in the case of 3 and 6, comparison of the experimental and computed shifts for the two stable rotamers indicates the predominance of the s-trans form in agreement with the results obtained in previous investigations. [9b,c,24,25a,c,27] We note that recently a combined NMR/ab initio calculation study has been performed to gain information on the preferred orientation of the C O group with respect to the C C double bond for some 4-carbamoyl-2,5-dihydro-2-iminofurans; [30] in fact, by comparing the experimental and computed values of the 1 J(C,C) of the carbons in α,β positions to the carbonyl and of the Cα,C( O) in the s-trans and s-cis conformation, it was established that the s-trans conformation is preponderant in solution. To check whether such an approach might also be useful on the benchmark molecules analyzed in the present work, we calculated the values of the mentioned coupling constants in the stable conformations, and it was found that the stereochemical behavior of 1 J(C,C) observed in Ref.…”

The quantum-chemical calculation of NMR indirect spin–spin coupling constants

“…[224][225][226][227]. For instance, in a study of iminodihydrofurans, calculated spin-spin coupling constants were compared with experimental data to establish the configuration of the C@NH group (orientation of the nitrogen lone pair) and the conformation of the O@CAC@C fragment (s-cis vs. s-trans) [226].…”

GIAO‐DFT calculation of 15N NMR chemical shifts of Schiff bases: Accuracy factors and protonation effects

“…Among the dozens of his disciples and followers all over the world, there are many prominent scientists and famous public figures known worldwide. About a quarter of a century ago, we published our first joint papers dealing with experimental and theoretical studies of NMR parameters of protonated acetone and acetone oxime together with some related items reviewed later by Krivdin and Contreras and Krivdin and Zinchenko . Now, we are back to this topic with new chemical diversity and new computational capabilities, but alas, Rubén is not with us anymore……”