Cyclic Vinyl p-Tolyl Sulfilimines as Chiral Dienophiles:  Theoretical Study on the Stereoselectivity, Lewis Acid Catalysis, and Solvent Effects in Their Diels−Alder Reactions

Abstract

The theoretical study reported in the present work deals with chiral cyclic vinyl sulfilimines and their reactivity as dienophiles in [4 + 2] cycloaddition reactions, using B3LYP/6-31G(d)//AM1 and B3LYP/6-31G(d)//B3LYP/6-31G(d) model chemistries. Consideration of Lewis acid catalysis, illustrated by BF(3), decreases the activation energies of the cycloaddition process while the charge transfer from the diene to the sulfilimine is augmented. The [4 + 2] cycloaddition reactions of sulfilimines with both furan and cyclopentadiene occur in the gas phase with endo stereoselectivity, which is more pronounced with the latter diene. Endo-exo energy differences in the gas phase with the B3LYP/6-31+G(d)//B3LYP/6-31+G(d), B3LYP/6-31G(d)//B3LYP/6-31G(d), and B3LYP/6-31G(d)//AM1 model chemistries are almost the same. Solvent effects are responsible for the inversion of the stereoselectivity in the reactions of sulfilimines with furan because of the great difference in the dipole moments in endo and exo approaches.

Synthesis of constrained analogues of tryptophan

“…Moving to the alkyl-substituted vinylindole 1b , the reaction yields equimolecular amounts of both conceivable diastereoisomers in CHCl 3 whereas toluene is the optimal solvent to achieve high diastereoselection (see Table 2 , entries 3 and 4). It is well known that reaction rates and selectivity in Diels–Alder reactions are affected by solvents [ 30 – 32 ]. In particular, polarity and hydrogen bond donor ability of the solvent can impact the diastereoisomeric ratios in a Diels–Alder reaction.…”

Reaction Mechanism of an Intramolecular Oxime Transfer Reaction: A Computational Study

“…Only a handful of similar computational and theoretical investigations have been published, but they have mainly concentrated on the hydrolysis and isomerization of oximes . Hence, it was necessary to obtain a preliminary picture from the oxime transfer reaction by computational investigation of a simpler formaldehyde oxime model systems (R 1 = R 3 = H, R 2 = Me) before performing calculations with the larger and more realistic acetone oxime model (R 1 = H, R 2 = R 3 = Me). , The solvent effect was included in the calculations because all experimental reactions have been done in nonpolar and aprotic solvents and because it has been shown in numerous studies that the presence of the solvent influences the reaction energy profile . Although both model systems investigated in this study are simplified if compared to the experimental setting, they were further simplified to lower the computational cost of calculations by omitting the weakly coordinating anion, such as the diphenylphosphate anion.…”

Polar Diels–Alder reaction of isoprene toward 2-bromocyclobutenone followed by a subsequent sodium hydroxide-assisted ring contraction reaction. A regio- and stereoselectivity and molecular mechanism study using DFT

“…1 One of the most well-known cycloaddition reactions is the Diels-Alder (DA) cycloaddition, which permits the rapid construction of a six-membered carbo-and/or a heterocycle from an s-cis 1,3-diene and a dienophile, with high stereo-and regioselectivity. [4][5][6][7][8][9][10][11] The simplest DA reaction between butadiene 1 and ethylene 2, affording cyclohexene 3, is presented in all text books as the prototype of the DA cycloaddition but this reaction requires harsh experimental conditions (see Scheme 1). 2 From the discovery of the DA reaction in the 1920s by Otto Diels and Kurt Alder, 3 a huge amount of experimental and theoretical study has been devoted for understanding the mechanism and the selectivity of these cycloaddition reactions, which can be found widely in the literature.…”