Syntheses from Pyridines

The alternative route, from tosylhydrazones 8 by treatment with base, usually morpholine, has been used for high yields of sensitive materials. Examples are the 7-acetylamino derivatives 9a and 9b (89T7041) and the 5-bromo derivative 

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Pyrrolopyridine derivatives, 103, can be synthesized from pyridine compounds containing amino, iodo, and/or nitro substituents <1999H(50)1065>. These compounds serve as analogues of melatonin. 

B. Synthesis of [1,2,4]Triazolo[1,5-<7]Pyridines 1. Syntheses from Pyridines... 

Cyclization on to a nitrile group gives the same type of product (409) (78JCR(S)407>. The parent mesoion from (406 R1=R2 = H) was originally synthesized from pyridine-2(lJJ)-thione and a-bromacetyl bromide, and by cyclization of 2-(2-pyridinethio)acetic acid in acetic anhydride (66BCJ1248). 

Table 2 Oxazocines 109 synthesized from pyridines, bis(trimethylsilyl)ketene acetals, and methyl chloroformates <2002CC940, 2005EJO3724>...

Pybox L8 (Fig. 4) was synthesized from pyridine-2,6-dicarboxylic acid and optically active amino alcohols via an amido chloride intermediate [ 16,23 ] or via BFj-catalyzed cychzation of intermediate amino alcohols [24]. The combination of Pybox-i-Pr (L8a) and [Rh(COD)Cl]2 (Rl) exhibited catalytic activity as an in-situ catalyst for the reduction of acetophenone (Kl) to give 76% ee (S) [16].However, the complex RhCl3(Pybox-z-Pr) R4a under assistance with AgBF4 accelerated the reduction in THF to give 94-95% ees [23]. Diphenylsilane (SI) was also the best silane in this system. Most aromatic methyl ketones were reduced in 90-99% ees, and reactions of levurinate KIO and 2-octanone Kl 1 resulted in 95% ee and in 63% ee, respectively. The Pybox-Rh catalyst R4a reduced selectively 2-phenylcyclohexanone K12 to give the S-alcohols for both trans- and cis-isomers PI and P2 in 96-99% ees [25]. The catalyst R4a can differentiate only the enan-... 

The 3,6-diposition-substituted pyridine compounds are important intermediates for industrial synthesis, especially for production of some agricultural chemicals. This compound can be obtained by chemically synthesized from pyridine, but the process is accompanied by some by-products. Microbial hydroxylation of aromatic compounds is a very efficient method of regioselective reaction. Several methods have been reported for the preparation of 3,6-disubstituted pyridine using microorganisms. In 1985, Lehky et al. reported the microbial production of 6-hydroxynicotinic acid (6-HNA) from nicotinic acid (NA) by Achromobacter xylosoxydans Nagasawa et al. also prepared 6-HNA from NA by using Pseudomonas fluorescens TN5. 

Imidazopyridines (IPs) may be synthesized from pyridine or imidazole derivatives by building up the second ring, and also by ring transformations from the other heterocyclic compounds. However, these methods are not of equal efficiency, and the most important preparative procedures utilize amino derivatives of pyridine as initial compounds for IP s synthesis. The main IP s precursors are o-diaminopyridines (o-DAP). 

A. Syntheses from Pyridines 1. Unsubstituted and Substituted Imidazopyridines... 

Coumarins and chromones containing pyridine substituents were synthesized from pyridine side-chain acids by employing the Knoevenagel, Pechmann, and Simonis reactions. The chromones XI-106 were obtained from a Simonis condensation of ethyl nicotinoylacetate (XI-105) with a variety of phenols (XI-104), whereas a Pechmann condensation yielded the coumarins (XI-107). 

Naphthyridine (XI-113) has been synthesized from pyridine side-chain acids via two different routes. Treatment of the dinitiile XI-108 with anhydrous hydrogen bromide yielded the naphthyridine (XI-107), Boiling XI-109 with hydrazine gave the dihydrazino naphthyridine Xl-110. The hydrazino groups... 

An alternative asymmetric Diels-Alder reaction was reported by the Fukuyama group in which a dihydropyridine derivative and acrolein were used to build the cyclohexene ring (Scheme 16.2). Dihydropyridine 10 was synthesized from pyridine 9 by NaBH4 reduction in the presence of Cbz-Cl. An asymmetric Diels-Alder reaction between the dihydropyridine 10 and the acrolein in the presence of MacMillan catalyst 11 at room temperature... 

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