Pyridines 1,2,3,6-tetrahydro-, 1-hydroxy

Thieno[2,3-c]pyridine, 2-amino-6-benzyl-3-ethoxycarbonyl-4,5,6,7-tetrahydro-biological activity, 4, 1015 Thieno[2,3-c]pyridine, 4,5,6,7-tetrahydro-biological activity, 4, 1015 Thieno[3,2-6]pyridine, 3-hydroxy-synthesis, 4, 1010... 

Unexpectedly strong intermolecular hydrogen bonding has been reported by IR spectroscopic studies for tetrahydro-4,7-phenanthroline-l,10-dione-3,8-dicarboxylic acids, which exist in the oxo-hydroxy form 165 in both solid state and in solution [78JCS(CC)369].Tlie conclusion was based on comparison of B-, C-, and D-type bands for 165 and their dimethyl esters (detection of hydrogen bonding) and on analysis of IR spectra in the 6 /xm region (pyridine- and pyridone-like bands). 

Most pyridines are reduced to the corresponding piperidines, but certain substituents, notably 2-amino and 2-hydroxy, tend to arrest the hydrogenation at the tetrahydro stage (55,56 7). Wenkert et ai. (llS) noted that in hydrogenation of any aromatic system capable of unmasking a stable, vinylogous amide unit, absorption may cease at this stage. An example is reduction of 3-acetylpyridine (I) to 2, a compound that resisted further attempts at reduction (31). 

Treatment of 3,6-dihydroxy-3,4-dihydro-2//-pyrido[2,l-h][l,3] thiazinium salt (86) with orthophosphoric acid at 140°C for 34 h or with cone, sulfuric acid at ambient temperature for 5 h afforded 1 1 and 3 1 mixtures of pyrido[2,l-6][l,3]thiazine (87) and thiazolo[3,2-a]pyridine (88), respectively (70ACS2949). Under basic conditions, only extensive destruction of 86 was observed. When 3-hydroxy-2,3,4,6-tetrahydro[l,3]thiazino[2,3-a]isoquinolin-6-one was left to stand in cone, sulfuric acid at room temperature overnight, 4,6-dihydro[l,3]thiazino[2,3-a]isoquinolin-6-one was obtained in 61% yield (72ACS1620). 9-Oxido-3,4-dihydro-2H-pyrido[2,l-h] [l,3]thiazinium betaine did not undergo cycloaddition even under extreme conditions [81JCR(S)208],... 

According to Yerma et al. [35] the mechanism of the reaction may be rationalized as involving (3-oxygenation of the bismuth(III) nitrate activated chalcone enolate, which may then undergo a Michael addition to a second a, 3-unsaturated ketone (Scheme 4.52) to form a 1,5-diketone enolate adduct 180. Subsequent heteroannulation with o-PDA via condensation and retro-aldol disproportionation may form 2-hydroxy-1,2,4,6-tetraaryl-1,2,3,4-tetrahydro-pyridine derivatives 181, which may undergo dehydration to yield 1,2,4,6-tetraaryl-1,4-dihydropyridines 177. 

To a solution of 350 mg of methyl 4-[2-endo-hydroxy-l-exo-hydroxymethyl-3a,8b-cis-2,3,3a,8b-tetrahydro-lH-5-cyclopenta[b]benzofranyl]butyrate in 3.5 ml of anhydrous dimethylformamide cooled in an ice bath were added 140 mg of imidazole and 360 mg of t-butyldimethylsilyl chloride, and after the mixture was stirred for 3 hours at room temperature, dimethylformamide was removed under reduced pressure. The residue was dissolved in a mixture of 10 ml of acetic anhydride and 5 ml of pyridine. After the mixture was stirred for 2 hours at room temperature, the reaction mixture was concentrated. 

To a solution of the (+)-methyl 2-[2-(N-phenylsulfonyl)indolyl]-2-hydroxy-3-[3-(N-allyl-5-ethyl-l,2,3,6-tetrahydropyridine)]propionate (a mixture of diastereomers at C-2) in dry dimethoxyethane at -50°C under argon was added sodium naphthalenide (1 M in THF). The mixture was quenched with trifluoroacetic acid, and extracted with ethyl acetate (3 times 10 ml). The extract was washed with saturated aqueous NaHC03 solution, dried (MgS04) and evaporated in vacuo to give the (+)-methyl 2-(2-indolyl)-2-hydroxy-3-[3-(N-allyl-5-ethyl-l,2,3,6-tetrahydro-pyridine )]propionate. The mixture of diastereomers was not separated but chromotagraphed over silica gel eluting with hexane/ethyl acetate/10% aqueous NH4OH/MeOH (5 1 1) to remove more polar impurities. 

To a solution of the S-(+)-4-acethoxy-9-[2-(5-ethyl-l,2,3,6-tetrahydro-pyridin-3yl)-l-(lH-indol-2-yl)-l-methoxycarbonyl-ethyl]-3a-ethyl-5-hydroxy-8-methoxy-6-methyl-3a,4,5,5a,6,ll,12,12b-octahydro-lH-6,12a-diaza-indeno[7,l-ca]fluorene-5-carboxylic acid methyl ester in dioxane and glacial acetic acid was added 37% aqueous formaldehyde and the mixture stirred at 35°C for 24 h. The solution was evaporated in vacuo and the residue suspended in chloroform and washed with cold aqueous 5% K2C03 solution. The chloroform layer was dried (MgS04), filtered, and evaporated. The residue was chromatographed eluting with EtOAc/MeOH, 10% NH4OH to give the product navelbine. 

Hydroxy-2-methyl-3-phenylpropyl)amino]pyridine (24) underwent dehy-drative cyclization to give 3-methyl-4-phenyl-l,2,3,4-tetrahydro-l,5-naphthyridine (25) (70% H2S04, 0°C —>25°C, 15h 65%) that was easily dehydrogenated to give 3-methyl-4-phenyl-l,5-naphthyridine (26) (neat substrate, Pd/C, 200°C, 3 h 56%).879 Also other examples.48 485 865 967 1232 1245... 

Ethyl 5-cyano-2-(a-cyanoethoxycarbonylmethyl)-4-oxo-l,4-dihydro-3-pyridine-carboxylate (42) gave ethyl 3-cyano-7-hydroxy-4,5-dioxo-1,4,5,6-tetrahydro-l,6-naphthyridine-8-carboxylate (43) (Et3N, EtOH, reflux, 3 h 65%).698... 

Reaction of l-(3,4-dimethoxybenzyl)-9-hydroxy-l,2,3,4-tetrahydro-8//-pyrido[l,2-a]pyrazin-8-one with 37% formaldehyde solution gave a tetracyclic tetrahydroprotoberberine analogue in a Mannich-type reaction (78AJC187). Reactions of 2,3,4,4a,5,6-hexahydro-l//-pyrazino[l,2-a]-quinolines with 1 W-pyrrolo[2,3-h]pyridine in the presence of 37% aqueous CH20 and AcONa in AcOH, and with 3-dimethylaminomethyl-l //-pyrrolo[2,3-h]pyridine afforded 3-[(l//-pyrrolo[2,3-h]pyridin-3-yl)methyl] derivatives (94MIP6 96USP5576319). 

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