Bases 4-Pyrrolidinopyridine

Pyrrolidinopyridine based polymers react faster with benzyl chloride than low molecular weight analogs. The polymer synthesized by cyclopolymerization of N-4-pyridyl bis(methacrylimide)... 

The hydroxy ketone G17 was obtained without event however, the key intramolecular acylation now provided a new set of challenges. First, the tertiary alcohol of G17 resisted acylation by a wide variety of phosgene-based reagents until a specific procedure, involving methylchloroformate, triethylamine, and 4-pyrrolidinopyridine was developed. However, the product proved to be the cyclic carbamate G18. The authors surmise that iV-acylation of G17 occurred first, which then facilitated intramolecular 0-acylation leading to G18. 

One specialized and readily available carbodiimide, called dicyclohexyl-carbodiimide (usually abbreviated DCC), will be used to illustrate this transformation it has structure 78. Use of this reagent to form esters led to the discovery that adding a catalytic amount of an amine base gives higher yields. This observation will be used, but will not be explained further in this discussion. When 3-methylbutanoic acid (77 isobutyric acid) is stirred with tert-butanol in the presence of a catalytic amount of 4-pyrrolidinopyridine (79), for example, er -butyl 3-methylbutanoate (80) is isolated in 65% yield. In addition to the ester, one molar equivalent of dicyclohexyl urea (see 87) is also isolated. The mechanism that explains these results begins by noting that the diimide carbon in 78 is like a double imine and bond polarization makes the central carbon atom very electrophilic. 

The well-known powerful basic catalyst 4-dimethylaminopyridine has been the inspiration for a new transesterification catalyst for a-hydroxy esters (5). The designer compound is 2-formyl-4-pyrrolidinopyridine (6). By the introduction of an aldehyde group into the pyridine ring at the 2-position, the ready formation from (5) of a hemi-acetal (7) makes possible, via a covalent pre-association step, a facile displacement by pyridine nitrogen of the aryloxy group of the a-hydroxy ester (5). The product of this process, a tricyclic pyridinium compound (9), is formed by a nucleophilic mechanism (Scheme 1, pathway b), and interaction with methanol then leads to the methyl ester of the a-hydroxy acid (10) and regeneration of the catalyst. However, a study of the mechanism of this catalytic process discounted the nucleophilic mechanism and provided clear evidence instead for a general base mechanism, which proceeds via a dioxolanone (8) (Scheme 1, pathway a) ... 

The grafting of nucleic acid base derivatives with a hydroxyl group onto poly(ethyleneimine) polymer backbone was also carried out by the activated ester method. Since the reactivity of the lactone is low, the direct reaction of the lactone derivative with poly(ethyleneimine) was not effective. Therefore, the lactone derivatives were at first hydrolyzed to the 3-hydroxybutyric acid derivatives, followed by condensation with poly(ethyleneimine) using the activated ester method. The grafting reaction was carried out in N,N-dimethylformamide, where a small amount of 4-pyrrolidinopyridine was added as an effective catalyst. Nucleic acid base contents of the polymers were determined by UV spectroscope of hydrolyzed samples. A quantitative calculations were made by using the corresponding carboxyethyl derivatives as standards. The nucleic acid base units (unit mol%) on the polymer are tabulated in Table 1. 

Dialkylamino)pyridines (Figure 1) behave either as weak bases or as nucleophiles via the sp -hybridized nitrogen atom. DMAP and 4-pyrrolidinopyridine (PPY), which are commercially available, are prototypes of such 4-aminopyridine derivatives. In molecular chemistry, these compounds have proven efficient in acylation transesterification reactions. Section 4.06.4 will discuss their use for the organocatalyzed ROP of carbonyl-containing heterocycles. 

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