Pyridine, Pyrrolidino

Ruble JC, Fu GC (1998) Enantioselective construction of quaternary stereocenters rearrangements of 0-acylated azlactones catalyzed by a planar-chiral derivative of 4-(pyrrolidino) pyridine. J Am Chem Soc 120 11532-11533... 

Dimethylamino)pyridine (1, DMAP) and its analogs, particularly 4-(pyrrolidino)pyridine (2, PPY) have acquired enormous importance and utility as supemucleophilic catalysts in synthetic organic and polymer chemistry (1, 2). 

We have previously (13) reported a rapid two step synthesis of 4-(pyrrolidino)pyridine copolymers via the reaction of commercially available maleic anhydride copolymers with 4-aminopyridine followed by reduction with LiAlH, yielding polymers with a high degree of functionalization. 

Treatment of 3-(2-pyrrolidino)pyridine with 2 molar equiv of diethyl acetylenedicarboxylate under microwave conditions gives the tetrahydropyrrolonaphthyridine 283 and (presumably) diethyl maleate or fumarate. Under conventional heating conditions, decarboxylated products are also observed (Scheme 71) <2005TL3953>. 

Triprolidine hydrochloride is E-2-[3-(l-pyrroli-dinyl)-l-p-tolylpropenyl]pyridine, monohydrochloride E-l-(2-pyridyl)-3-pyrrolidino-l-p-tolylprop-l-ene, monohydrochloride. ... 

Hence, the group developed a series of planar chiral ferrocenyl 4-DMAP and 4-(pyrrolidino)pyridine (4-PPY) derivatives (15-18) that have proved to be highly versatile and efficient catalysts for many acyl transfer processes (Fig. 5) [25, 26, 66-82, 93, 99, 103, 105]. 

It is known that 5-acyloxyoxazoles 132 rearrange to 4-acyl-5(4/l/)-oxazolones 133 in the presence of 4-(dimethylamino)pyridme or 4-(pyrrohdino)pyridine. Recently, an asymmetric variant of this nucleophUe-catalyzed rearrangement that employs a chiral derivative of 4-(pyrrolidino)pyridine has been described. This procedure allows the construction of quaternary stereocenters with high levels of enantioselectivity (Scheme 7.38). Representative examples of saturated 5(4//)-oxazolones prepared via sigmatropic rearrangements are shown in Table 7.16 (Fig. 7.18). 

Planar-chiral derivatives of 4-(pyrrolidino)pyridine (PPY) have been reported as efficient catalysts for enantioselective Staudinger reactions [75]. These chiral derivatives catalyzed the reactions between a range of symmetrical and unsymmet-rical disubstituted ketenes and a wide imine array leading to (3-lactams with good stereoselections and yields. 

The Staudinger reaction, catalyzed by 4-(pyrrolidino)pyridine derivative, could be controlled through the appropriate choice of the /V-protecting group of the imine... 

In 1970 Steglich and Hofle reported that 4-dimethylaminopyridine (DMAP) and 4-(pyrrolidino)pyridine (PPY) are excellent catalysts for isomerization of O-acyl azlactones E to their C-acylated isomers F [79-81], In this rearrangement, a new quaternary stereocenter is generated (Scheme 13.41). Clearly, DMAP or PPY afford the rearrangement products F in the racemic form. 

Poly(L-glutamate)s containing various molar percentages of spiropyran units in the side chains (XV) have been prepared by treating poly(L-glutamic acid) with N-(2-hy-droxyethyl) -spiropyran in the presence of dicyclohexylcarbodiimide and 4-pyrrolidino-pyridine.[60 62] The structure and photochromic behavior of the modified polymers are shown in Figure 8. 

It has also been demonstrated that a planar-chiral azaferrocene derivative of 4-(pyrrolidino)pyridine is an excellent catalyst for the enantioselective Staudinger reaction, providing P-lactams 24 with very good stereoselection and yield <02JACS1578>. 

Simple amines can rapidly add to ketenes in the absence of a catalyst, but less reactive nitrogen nucleophiles such as the pyrroles do not react at room temperature with ketenes such as phenyl ethyl ketene <2002JA10006>. In contrast, additions can proceed swiftly when planar chiral 4-(pyrrolidino)pyridine (PPY) derivative 235 is employed as a catalyst (Equation 58). In the presence of enantiopure PPY derivative 235 and an appropriate pyrrole, the A -acylpyrroles 236 and 237 can be generated in high enantiomeric excess (Equations 58 and 59) <2002JA10006>. With pyrrole itself as the nucleophile, the new stereocenter is produced in moderate ee (42%). It was discovered that l-acyl-l/7-pyrrole-2-carbonitriles 236 can be converted into a wide array of useful compounds with essentially no erosion in enantiomeric excess. 

Propin 1-Pyrrolidino- V/2a, 306f. Pyridin 3,4-Dimethyl-l, 2-dihydro-V/lc, 1078 Pyrrol... 

REAGENTS - Esterifiaation - Carboxylic acids can be esterified in high yield under very mild conditions by a new procedure using DCC and 4-(N-pyrrolidino)pyridine. The procedure gives good yields even with mesitoic acids or with tertiary-butanol. °... 

A similar mechanism is thought to be involved in the formation of a-trilluoromethyl ketone 7 instead of expected amine 6 during the reaction of iminium salt 5 with CF3Br under Barbier conditions (equation 4) . It was proposed that pyridine probably transforms iminium ion 5 into the enamine (l-pyrrolidino)-l-cyclohexene by elimination of HQ, which then undergoes a radical chain reaction with CF Br as shown in Scheme 1 to give 7. This is supported by the observation that no condensation products are observed when iminium salts lacking removable a-hydrogens are used. 

Utilization of l-methyl-2-methylthio-2-pyrroline as a dienophile to react with 200 produced the l-methyl-6-(/3-D-ribofuranosyl)pyrrolidino[3,2-c] pyridine 201 (95AP175) (Scheme 59). 

The same reaction was studied with soluble polymer 38, prepared by polymerization of 4-(N,N-diallylamino)pyridine. This catalyst was even more efficient than 37 or 4-(pyrrolidino)pyridine, a base with much higher activity than DMAP [177]. 

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