Condensation-cyclization reactions of electron-deficient aromatics. VII. Kinetics and mechanism of carbanionic .sigma.-complex formation and cyclization

Abstract

Saponification of 7 gave 2-ethylidene-3-methylglutaric acid as needles from benzene-hexane, mp 129-130°(lit.16 mp 129°).

Mechanism and linear free energy relationships in the kinetics of formation of bicyclo[3.3.1]nonane derivatives from 1,3,5‐trinitrobenzene, phenyl‐substituted 1‐benzyl‐1‐(ethoxycarbonyl)‐2‐propanones, and triethylamine

“…A very slight increase in the rate with increasing concentration of \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}$\displaystyle\mathop{\mbox{N}}\limits^ +$\end{document} Et 4 can be attributed to the stabilization of increasing charge in the transition state leading to dianionic intermediate. The mechanistic picture of the present work is comparable with that of Strauss et al 10, who have worked with symmetrical ketone (dibenzylketone).…”

“…Addition of NEt 3 to a solution of BEP and TNB in CH 3 CNCH 3 OH (50% v/v) gives rise immediately upon mixing to a visible spectrum with two maxima at 450 and 570 nm characteristic of 1:1 Meisenheimer adduct, and this rapidly changes to give a peak at 500 nm owing to the formation of the bicyclic adduct. As reported earlier 10,14, in the present study, the slow disappearance of 1:1 adduct during the formation of a bicyclic adduct has been followed by observing the decrease in optical density at 570 nm.…”

“…The growing interest in examining the steric effects caused by the substituents during the cyclization of 1:1 sigma adduct prompted us to isolate a series of crystalline adducts containing the bicyclo[3.3.1]nonane skeleton from the carbanions of beta keto esters and TNB in our laboratories 6. Although a number of carbon‐bonded sigma complexes and bicyclic adducts have been isolated in the crystalline form and characterized 2–9, there are relatively few 3,10–15 comprehensive kinetic and thermodynamic studies of their formation because some carbon nucleophiles are difficult to generate under conditions suitable for studies. Structure–reactivity correlation studies, which are effective tools in deducing the reaction mechanism in their formation and decomposition, are still more limited.…”

“…Structure–reactivity correlation studies, which are effective tools in deducing the reaction mechanism in their formation and decomposition, are still more limited. A search of the literature indicates that only a few reports have so far appeared on the structure–reactivity correlations in the conversion of sigma complexes to bicyclo[3.3.1]nonane derivatives 3,10,13,14. Attempts have now been made to expand the scope of correlation analysis in the formation of bicyclic adducts.…”

Carbanion additions and cyclizations involving anionic .sigma. complexes. Meta bridging reactions of aromatics

“…Base abstraction of H7 in 5 followed by intramolecular attack at C.g yields 6a or 6b. The abstraction in 5a is facilitated by strong base (i.e., sodium hydroxide49), whereas in 5b it is facilitated by the presence of the electron-withdrawing groups R. 39,45 The unreactivity of the trialkylaiqmonium salt of 5a in solutions of tertiary amine is thus understandable since in the presence of weak base the nonacidic H7 is not readily removed. If the conjugate acid of the base used to form 6 is sufficiently strong, protonation of the unconjugated nitronate function in 6 leads to 7.…”