Studies in the ring chain tautomerism

Abstract

The thesis entitled “Studies in Ring–Chain Tautomerism” is divided into five chapters.

Chapter I The first chapter gives a brief introduction to the present work. Various interactions such as ring–chain tautomerism, neighbouring group participation, neighbouring group catalysis, steric hindrance and steric assistance, and field effects that are brought into play when two groups are near each other, are briefly discussed.

Chapter II The second chapter describes the ring–chain tautomerism of o-benzoylbenzamides and their derivatives. The effects of substituents in the o-position to the keto group, on the nitrogen, and in the amide?bearing ring on the equilibrium have been studied. The influence of solvents on the keto?amide ? hydroxy?lactam equilibrium is also investigated. Polar solvents are found to favour the cyclic form. The results are explained in terms of a carbonyl addition–dissociation model.

Chapter III In the third chapter, reactions of the pseudo?acid chloride of o-benzoylbenzoic acid with fourteen nucleophiles of various structural types have been discussed. Weak nucleophiles are found to react at the tetrahedral carbon, leading to a pseudo?derivative, whereas strong nucleophiles react at the lactone carbonyl, leading to opening of the lactone ring to give a dicarbonyl compound. An explanation has been advanced to account for this dichotomy.

Chapter IV The fourth chapter is divided into two sections. Section A Section A describes the dimerization of pseudo?acid chlorides with sodium iodide in acetone to give a mixture of stereoisomeric dilactones (d,l and meso). Pseudo?acid chlorides of o?(p-substituted benzoyl)benzoic acids, phthaldehydic acid, phthalic acid, and mucobromic acid are found to give dilactone mixtures. The stereochemistry and mechanism of formation of dilactones involving radical intermediates have been discussed. Section B Section B describes detailed kinetics of the dimerization of o-benzoylbenzoic acid chloride with potassium iodide in anhydrous dimethylformamide. The rate expression for the dimerization is: Rate=k2[acid chloride][KI]\text{Rate} = k_2 [\text{acid chloride}] [\text{KI}]Rate=k2?[acid chloride][KI] Electron?donating groups in the 4??position slightly increase the rate, and electron?withdrawing groups slightly decrease it (? = –0.36). A good correlation is obtained between the rate constants and ?? values. Activation parameters and the reaction constant have been evaluated.

Chapter V The kinetics of the alkaline hydrolysis of methyl ??benzoylpropionate, methyl ??benzoylbutyrate, methyl ??benzoylvalerate, and their desoxy analogues have been described in the fifth chapter. The rate is found to decrease in the order: methyl ??benzoylpropionate > methyl ??benzoylbutyrate > methyl ??benzoylvalerate The results are explained in terms of carbonyl?assisted ester hydrolysis.