377. Aspects of stereochemistry. Part II. Intramolecular electrophilic assistance of displacement reactions

Abstract

If, in a monoester of a 1 : 3-diol, the hydroxyl and ester groups are held close together by their molecular environment, hydrogen bonding to the alcohol oxygen of the ester occurs. Such hydrogen bonding facilitates hydrolysis of the ester, and in cyclohexane compounds the usual rule whereby equatorial esters are more easily hydrolysed than axial esters can be reversed. The r61e of the neighbouring hydroxyl group in these reactions may be regarded as that of an intramolecular electrophil.WITH the intention of finding suitable conditions for selective hydrolyses of 3-acetoxy-5hydroxy-steroids, aqueous potassium hydrogen carbonate was studied, and conditions were thereby found under which a cis-diaxial hydroxy-ester was largely hydrolysed whereas non-hydroxylated esters were unchanged. The four 3-acetoxy-5-alcohols of the (I1 ; 7O0/0) ( I l l ; 1 3 % ) ( 1 V ; 7 8 % ) ( I ; I 8 O I 0 ) cholestane and coprostane series were therefore treated with potassium hydrogen carbonate solution under identical conditions-the percentage hydrolysis of each is shown below the formulae (1)-(IV). The facilitating effect of a hydroxyl group cis to an ester group part I, preceding paper.

Isotopic and Kinetic Studies of the Mechanism of Hydrolysis of Salicyl Phosphate. Intramolecular General Acid Catalysis

“…The reaction scheme may be drawn formally as shown in eq. 4. There are a number of pieces of evidence which are consistent with this mechanism.…”

Intramolecular Catalysis in the Hydrolysis of p-Nitrophenyl Salicylates

“…Hydrolysis of p-Nitrophenyl 5-Nitrosalicylate.-The pH-rate profile of the hydrolysis of />-nitrophenyl 3.-pH dependence of the reaction of azide ion with %nitrophenyl 5-nitrosalicylate in 34.4% dioxane at 25°; [N3~] = 0.656 M, [ester]» = 6.48 X 10-= M. nitrosalicylate shown in Fig. 4 is an extraordinary profile for an ester hydrolysis. The log k vs. pH profile for a simple ester such as ethyl acetate is a Vshaped curve, the left-hand side corresponding to a hydronium ion-catalyzed hydrolysis and the right-hand side corresponding to a hydroxide ion-catalyzed hydrolysis.…”

Hydrolysis of gibberellin 7-methyl esters: anchimeric assistance by a 15-alcohol

“…286 (8). 270 (14), 242 (9), 241 (9), 225 (9), 213 (7), 185 (9), 159 (8) and 91 (12). I 5r.-Hj.clroxygihherelliti A,, 7,15-1uctonr 34 (7 mg) gave 15%hydroxy-GA,, 25 (5 mg) whose ' H NMR and mass spectra were identical to those previously obtained.…”