Abstract
The electrophilic reactivity of a series of 8-arylated vinyl p-quinone methides (pVQMs) was determined by analyzing the kinetics of their reactions with carbanions in DMSO at 20 °C according to the linear free energy relationship log k = sN(N + E). The electrophilicity parameters E for pVQMs were used to successfully predict Michael-additions with structurally diverse C-, N-, S-, and H-nucleophiles.
Highlights
The interest in vinyl p-quinone methides[1−4] increased recently because it was shown that applying a 1,6-addition/cyclization strategy in reactions of pVQMs with sulfonium ylides,[5] carbanions,[6] or ammonium ylides7a gave rise to vinyl cyclopropanes that rearranged to chiral spirocyclopentenes
PVQMs are integrated into Mayr’s reactivity scales, which allows chemists to reliably predict the scope of their reactions with
The pVQMs 1a−d were synthesized according to literature procedures and characterized by spectroscopic and electrochemical methods (Supporting Information)
Summary
We have characterized the Mayr electrophilicities E of the vinyl p-quinone methides 1a−d by analyzing the kinetics and products of their reactions with carbanions in DMSO. In agreement with earlier findings on the regioselectivities of nucleophile additions to 2,6-dimethoxy-4-(2propenylidene)-2,5-cyclohexadien-1-one and eugenol-derived vinylic p-quinone methides,1c,3 the pVQMs 1 are ambident electrophiles that have similar 1,6- and 1,8-reactivities. While the results of our experiments do not allow us to predict the regiochemistry of the nucleophilic attack at pVQMs, the determined Mayr E parameters reliably reflect the general electrophilic reactivity of these electron-deficient π-systems. Application of the electrophilicity parameters E in eq 1 rationalizes reported reactions and empowers chemists to systematically predict novel combinations of pVQMs with nucleophiles. Mario Waser − Institute of Organic Chemistry, Johannes Kepler University Linz, 4040 Linz, Austria; orcid.org/0000-00028421-8642.
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