Stereocontrol of intramolecular Diels–Alder reactions by an allylic diphenylcyclopropyl group

Abstract

Intramolecular Diels-Alder reactions of ester-linked 1,3,8-nonatrienes carrying a diphenylcyclopropyl substituent attached to C1 proceed with high levels of stereoselectivity. The stereochemical outcomes of these reactions are explained by reference to B3LYP/6-31G(d) transition structures. Experimentally, the diphenylcyclopropane rings remain intact through these IMDA reactions, notwithstanding their predicted extremely high degree of asynchronicity (the B3LYP-computed lengths in the IMDA transition structures differ by as much as 1.1 angstroms), providing support to the notion that these reactions are concerted processes.

Case Studies on Developments of the Internet in Latin America: Unexpected Results

“…Parenthetically, we draw attention to the extraordinarily long developing “bond” —exceeding 3.0 Å— between the diene and the thionoester‐bearing carbon atom in the intermolecular endo ‐ 12 TS (Scheme ). The degree of bond asynchronicity (>1 Å) in this TS is unusually high for a non‐Lewis acid catalyzed DA reaction 16. 41a The B3LYP/6‐31+G(d) wavefunction for endo ‐ 12 TS is stable with respect to all perturbations treated by the GAUSSIAN 03 program,46 including relaxation of the wavefunction from restricted to unrestricted, thereby indicating insignificant biradical character in the wavefunction.…”

“…Consequently, endo ‐ 12 TS represents a case of an extremely asynchronous but concerted DA reaction in which one of the developing bonds, at 3.0 Å in length, is barely a bond at all. Such a high degree of asynchronicity, while not uncommon in Lewis‐acid‐catalyzed DA reactions,47 is unusual for an uncatalyzed DA reaction 16…”

Photochemische Carbentransferreaktionen von Aryl/Aryldiazoalkanen – Experiment und Theorie**

“…For example, donor/acceptor carbenes exhibit a singlet ground state in chlorinated solvent as demonstrated both experimentally and computationally. [3] This singlet carbene can be accessed via the photolysis of donor/acceptor diazoalkanes and utilized in carbene transfer reactions, as recently demonstrated (2, Scheme 1b). [9] Contrarily, the spin state of aryl/aryl carbenes is much more dependent on the nature of the electronic properties of the substituents of the aromatic ring.…”

“…[1] In this context, experimental and theoretical studies on the influence of electronic effects on the carbene spin state remains a central area of research in physical organic chemistry. [1][2][3][4][5][6][7][8] In particular, matrix-isolation, ultrafast spectroscopy, or latest developments in computational chemistry represent important state-of-the-art techniques to characterize short-lived carbene intermediates. [2][3][4][5][6][7][8] These studies demonstrated that the electronic properties of substituents significantly impact on the spin state of carbenes and their singlet-triplet splitting.…”

“…[1][2][3][4][5][6][7][8] In particular, matrix-isolation, ultrafast spectroscopy, or latest developments in computational chemistry represent important state-of-the-art techniques to characterize short-lived carbene intermediates. [2][3][4][5][6][7][8] These studies demonstrated that the electronic properties of substituents significantly impact on the spin state of carbenes and their singlet-triplet splitting. For example, donor/acceptor carbenes exhibit a singlet ground state in chlorinated solvent as demonstrated both experimentally and computationally.…”