Facial Selectivity in the Diels−Alder Reactions of 5-Chloro-, 5-Bromo-, and 5-Iodo-1,3-cyclopentadiene and Derivatives

Abstract

A variety of dienophiles was used to assess the facial selectivity of Diels−Alder reactions in a series of 1,3-cyclopentadiene derivatives (1−3, 6−10) in which chlorine, bromine, and iodine were plane-nonsymmetric atoms pitted against hydrogen or methyl at C-5. The results were rationalized in terms of the major factor controlling the facial selectivity being related to steric hindrance between the diene and the dienophile. Selectivity did not correlate with reactivity. Facial selectivity in the reactions with 4-phenyl-1,2,4-triazoline-3,5-dione as the dienophile was also influenced by a second significant factor, postulated to be filled-orbital repulsion with the halogen substituent.

Understanding the Regioselective and Molecular Mechanism of the TCE in Cycloaddtion Reaction (TCE+Cp) and Addition Reaction (TCE+HCl) using DFT calculation

“…That is, P1 is formed 10 8 times faster than P4, in complete agreement with experimental outcomes [23,24]. Optimized geometries of TSs involved in these reactions, including some selected bond distances and the corresponding unique imaginary frequencies, are given in Scheme 4…”

“…FMO analysis has also been used to explain the regioselectivity patterns observed in Diels-Alder reactions of substituted systems [17,18], the transition state theory (TST) [19,20], and more recently static reactivity indexes defined within the conceptual density functional theory (DFT) [21]. Aim in this work is to present a theoretical study of the reactivity of tetracyanoethelene with Cyclopentadiene (Cycloadditions Reactions) and reactivity of tetracyanoethelene with Hydrochloric acid (additions Reactions) (Scheme 1) and compared the results of our calculations with experimental results available in the literature [22,23]. …”

Total Synthesis, Relay Synthesis, and Structural Confirmation of the C18-Norditerpenoid Alkaloid Neofinaconitine

“…Although the dienophiles approach exclusively from the sterically more-accessible face of the diene in that report, contrasteric cycloadditions of heteroatom-substituted cyclopentadienes have been reported elsewhere, 16 and selectivity has been shown to be substrate dependent. 16c …”

Non-degenerate 1,2-silyl shift in silyl substituted alkyltrimethylcyclopentadienes

“…The most important factor indicating the stability of 11 towards the retro-Diels-Alder reaction is the length of new C-C bonds. Whereas the C3-C4 value (1.608(2) Å ) lies in the range typical for new formed bonds in other Diels-Alder adducts of TCNE with, e.g., chlorocyclopentadiene (1.604 and 1.607 Å ) [23], chloropentamethylcyclopentadiene (1.602 and 1.603 Å ) [23], 6,6-dimethylfulvene (1.601 and 1.607 Å ) [24], isodicyclopentadiene (1.591 and 1.600 Å ) [25], and (trimethylsilyl)indene (1.582(2) and 1.593(8) Å ) [7], the C1-C2 length of 1.628(2) Å is significantly longer, apparently due to a steric hindrance of neighbouring iso-propyl group. These structural data are in agreement with a facile decomposition of 11 to starting materials as it was Table 1 Activation parameters obtained from an Eyring plot for b !…”