Can Remote Substituent Effects Influence Reactivity and Stereoselectivity in the Diels-Alder Cycloadditions of p-Substituted 6-Phenyl-6-methylfulvenes?

Mechanistic Investigations of the Pd‐Catalyzed Hydrogenolysis of Ketene Heterodimer β‐Lactones

“…Hammett plots of diastereoselectivity (dr, % major diastereomer/% minor diastereomer) vs. aryl substituent σ values have been used by various groups to extract useful mechanistic information about a range of reactions (radical reactions, aminohydroxylations and Diels-Alder reactions). [20][21][22] The non-linear relationship between diastereoselectivity (Table 2) and the aryl substituent σ values in our study was clear from the Hammett type plot shown in Figure 1. Such non-linearity may be suggestive of a change in reaction mechanism or a change in the rate-determining step, on changing substituents (e.g.…”

An overview of the cycloaddition chemistry of fulvenes and emerging applications

“…Furthermore, the nature of the substituents on the exocyclic carbon influences the fulvene reactivity and stability (Scheme 2) [30,42,48,52–54 64,67,69,71]. An ab initio study by Krygowski et al [15] reported that pentafulvene derivatives (not aromatic in the neutral form), when substituted with electron-withdrawing groups (EWG) (e.g., CN) or electron-donating groups (EDG) (e.g., O, N) on the exocyclic C6-position, exhibited anti-aromatic and aromatic ring currents, respectively [5,29,64,67,72].…”

“…In addition, substituents that are distant, but conjugated to the fulvene group, influence the aromaticity of the molecule [69,71], ultimately allowing modification of the molecule’s reactivity for a given reaction. This was demonstrated in a study by Gugelchuck et al [71], where the reaction rate of various p -substituted 6-phenylpentafulvenes with maleimides was investigated.…”

“…In addition, substituents that are distant, but conjugated to the fulvene group, influence the aromaticity of the molecule [69,71], ultimately allowing modification of the molecule’s reactivity for a given reaction. This was demonstrated in a study by Gugelchuck et al [71], where the reaction rate of various p -substituted 6-phenylpentafulvenes with maleimides was investigated. Substituents of an electron-donating nature (e.g., H, halogens) generally increased the reaction rate through stabilisation of the Diels–Alder transition state, whilst those which were electron-withdrawing (e.g., NO 2 , CN, NMeAc) decreased the reaction rate.…”

“…Substituents of an electron-donating nature (e.g., H, halogens) generally increased the reaction rate through stabilisation of the Diels–Alder transition state, whilst those which were electron-withdrawing (e.g., NO 2 , CN, NMeAc) decreased the reaction rate. Interestingly, strong EDG (e.g., OMe, NMe 2 ) exhibited a slower reaction rate than predicted, but this is likely due to the increased stabilisation of the reactant, rather than the transition state [71].…”