Ring opening, hydrolytic

An example of hydrolysis is the hydrolytic ring opening of the imide units in the phthalocyanine... 

Scheme 7.—The hydrolytic ring opening of pyramine, producing fragments in which the specific activity of each carbon can be estimated.

However, more-rigorous treatment (5% acetic acid, 100°C, 17 hours) opened the imidazole ring and produced /V -cyclohexyl-a-formylaminoacetamidine (57), characterized as the crystalline picrate. Amidine 57 produced no dye in the Bratton-Marshall assay. The same behavior can be expected from AIR (46), although the product of hydrolytic ring-opening was not actually isolated. On the other hand, it was observed that a solution of AIRs (0.2 mM in 0.01-M ammonium hydroxide) prepared by biosynthesis, when stored at 4°C, did not change appreciably within a day. A decrease in the concentration of AIRs of about 30% occurred within a month. 

There are three methods by which we commercially manufacture nylons. We make nylons of the AB type by hydrolytic ring opening reactions of lactams and the self condensation of co-amino acids. Nylons of the AABB type are made from diamines and diacids via an intermediate know as a nylon salt. 

We make type AB nylons, such as nylon 6 and nylon 12, by the hydrolytic ring opening of lactams in the presence of water at temperatures of about 260-270 °C. 

The polymerization process for nylon 6 consists primarily of the three types of reaction illustrated in Fig. 23.6. Each of the reactions is reversible, tvith the equilibrium of the products being controlled primarily by the concentration of water in the reaction vessel. The reaction is initiated by the hydrolytic ring opening of caprolactam to form 6-aminohexanoic acid, as shown in Fig. 23.6 a). Chain extension of the type shotvn in Fig. 23.6 b) dominates when water is abundant (10 to 20%) in the reaction mixture. At lower water levels (2 to 5%) chains grow primarily by the mechanism shown in Fig. 23.6 c). In order to limit the average molecular... 

Why does water content affect the chain extension step of the hydrolytic ring opening of caprolactam ... 

Reaction between 34a, chloropentafluorobenzene, and 1 equiv of water in polar aprotic solvents produced the tricyclic 45 by hydrolytic ring opening between the bridgehead atoms. Under similar conditions 34b afforded two isomeric compounds, 46 and 47 by ring opening between the N(9)-C(9 ) atoms (Scheme 2) <2003JOC3139>. 

Hydrolytic ring opening of the 1,3-oxazine ring of the tetrahydro-[l,3]oxazino[3,4- ][l,2]oxazin-8-one 389 and subsequent protection of the carboxyl group has been performed (Scheme 61) <1999TL4391>. 

Ring opening of the tricyclic thiadiazoloquinazolone derivative 84 was described by Santagati et al. <1994PHA880> the transformation is shown in Scheme 10. When this compound was heated with sodium hydroxide in a mixture of ethanol and dioxane, the central pyrimidine ring underwent hydrolytic ring opening, and the substituted thiadiazole derivative 85 was formed. 

Hydrolytic ring opening of the isomeric [l,2,3]triazolopyrimidinium salt 99 yielded the amide 100. The same team also described <1997T9393> the analogous transformation of the [l,2,3]triazolo[l,5- ]pyrazinium salts 101 reaction of this quaternary salt with a secondary amine (e.g., with pyrrolidine) led to the formation of the azadieneamine 102. For the formation of this product, a similar mechanism to that with 96 was anticipated. 

The greater CH acidity of Meldrum s acid (ptfa 4.97), compared with the malonic esters, results in a more rapid mono- and dialkylation. Concomitant hydrolytic ring opening may occur under liquidtliquid two-phase conditions and yields of the monoalkyl-ated product tend to be low (30-40%) [ 111 ], but the ring is retained under non-aqueous solidtliquid two-phase conditions [112, 113]. Further alkylation of the monoalkylated derivatives with a second (different) alkylating agent is possible [112, 113]. 

A large variety of metabolic cyclization reactions, counterparts to the reactions of hydrolytic ring opening discussed above, occur without any change in the degree of oxidation, and often nonenzymatically. Such reactions proceed by various mechanisms of intramolecular nucleophilic substitution, with elimination of amine, phenol, halide, or H20. 

Chapt. 5 is entirely devoted to the hydrolytic ring opening of lactams. The reverse reaction, namely lactam formation by cyclization-dehydration, has been seldom reported in the literature, suggesting that the reaction is, indeed, uncommon. However, it is also conceivable that lactam formation has sometimes been overlooked, and that much remains to be discovered regarding structural conditions for lactam formation, the factors that influence the lactam/amino acid equilibrium, and the role of enzymes. 

Michael Reaction. 5(47/)-Oxazolones undergo base-catalyzed conjugate addition to activated unsaturated compounds to afford the corresponding C-4 Michael adducts. For example, base-catalyzed addition of a 4-monosubstituted-5(4//)-oxazolone 157 to methyl propiolate yields a mixture of diastereomeric methyl 3-(5-oxo-2-phenyl-2-oxazolin-4-yl)acrylates 158. Hydrolytic ring opening of 158 and subsequent oxidation with lead tetraacetate affords 3-acylacrylates 160... 

When carbonyl compounds are used as electrophiles reaction with 4-monosub-stituted-5(4//)-oxazolones affords substituted serines after subsequent hydrolytic ring opening of the initial aldol product. As an example, 4-methyl-2-phenyl-5(4//)-oxazolone 193, prepared from alanine, reacts with benzaldehyde in a base-catalyzed addition to give, after hydrolysis, a 3 1 mixture of threo- and... 

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