Hydrolysis, acetal imine

Substituted a-amino esters can be prepared by hydrolysis of imines obtained by alkylation of imine (51) with allylic acetates or... 

Sonochemical acetalization of carbonyl groups are known in carbohydrate chemistry. The formation and hydrolysis of imines were described in a few cases. 

The preparation and hydrolysis of imines can be considered parallel to those of acetals. Such a process is used to prepare a pyrazole ring from p-diketones derived from fatty esters (Eq. 33). No catalyst is necessary. 

Hydrolysis of acetals, imines, and enamines under acidic conditions produces ketones or aldehydes. 

Comforth has reviewed literature reports and independently studied the special cases of reaction of 1 with salicylaldehyde and with 2-acetoxybenzaldehyde. Coumarins (10) are afforded in the condensation of 1 with salicylaldehyde or its imine, whereas when 2-acetoxybenzaldehyde is used, acetoxy oxazolone 12 is the major product. The initial aldol condensation product between the oxazolone and 2-acetoxybenzaldehyde is the 4-(a-hydroxybenzyl)oxazolone 11, in which base-catalyzed intramolecular transacetylation is envisioned. The product 9 (R = Ac) can either be acetylated on the phenolic hydroxy group, before or after loss of acetic acid, to yield the oxazolone 12, or it can rearrange, by a second intramolecular process catalyzed by base and acid, to the hydrocoumarin, which loses acetic acid to yield 10. When salicylaldehyde is the starting material, aldol intermediate 9 (R = H) can rearrange directly to a hydrocoumarin. Comforth also accessed pure 4-(2 -hydroxyphenylmethylene)-2-phenyloxazol-5(4//)-one (13) through hydrolysis of 12 with 88% sulfuric acid. 

Aryl alkyl amines gave hydroxylamine 0-arylsulfonates when reacted with arylsul-fonyl peroxide. The products were later decomposed to azomethine and further hydrolysis results in the corresponding amine with one less carbon atom. Thus when p-methoxy-benzylamine was treated with p-nitrophenylsulfonyl peroxide at —78 °C in ethyl acetate, p-methoxybenzaldehyde and p-methoxyaniline were obtained . Cyclic amines with p-nitrophenylsulfonyl peroxide were converted to the Al-(p-nitrophenylsulfonyloxy)amine derivatives, which further rearranged to ring-expanded cyclic imines in good yields (equation 9 f. ... 

Since N-nitrosoimmonium ions seem to be involved in the hydrolysis of a-acetates, it should be possible to isolate such species as stable salts. For this purpose, we selected a system such as XVII in which the phenyl group should provide further stabilization of such a carbonium ion. After the reaction of nitrosyl chloride with the corresponding imines, addition of antimony pentachloride resulted in the precipitation of pale yellow solids these could be isolated and stored under nitrogen for several days at room temperature. ... 

The acidic aqueous layer from the aqueous acetic acid/sodium acetate/pentane hydrolysis of 2-alkylcyclo-hexanonc imines is neutralized with solid potassium hydroxide to pH 14, and then saturated with sodium chloride. This aqueous solution is extracted with four portions of diethyl ether, and the combined ethereal layer is washed with brine. Drying over potassium carbonate and concentration gives an oil which is distilled 85% recovery bp 57-59 °C/0.02 Torr [x]D — 13.75 (c = 5.8, benzene). If the rotation of the distilled amine is lower than 13.40, it is purified via its hydrochloride. Thus, a solution of the amine in ice-cold diethyl ether is treated with dry hydrogen chloride by bubbling through a fritted disk. The amine hydrochloride is collected by filtration and recrystallized from ethanol mp 151-152°C. 

In contrast, 2-methylcyclohexanone and 2-methylindanone were racemized during imine hydrolysis with sodium acetate/acetic acid/pentanc/water8. In the preparation of 2-isopropyIcy-clohexanone and 2-isopropyl-6-methylcyclohexanone enantiomeric excess of the final products was low due to racemization8. 

The fact that true general acid catalysis is correct for the slow step in Scheme 9 is established for the hydrolysis of benzylidene-f-butylamine (21) at pH 4 to 5, conditions sufficiently basic that hydration is still the rate-determining step, as shown in Scheme 9, but acidic enough that essentially all of the imine exists in the protonated form. Under these circumstances, the hydrolysis (reverse of Scheme 9) is subject to general base catalysis by acetate ion.97 This... 

Takemoto and coworkers extended their palladium-catalyzed asymmetric allylic alkylation strategy using allyl acetate and chiral phase-transfer catalyst to the quaternization of 13 [23b]. A correct choice of the achiral palladium ligand, (PhO P, was again crucial to achieve high enantioselectivity and hence, without chiral phosphine ligand on palladium, the desired allylation product 15 was obtained with 83% ee after hydrolysis of the imine moiety with aqueous citric acid and subsequent benzoylation (Scheme 2.12). 

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