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Dihydropyridines hydride reduction

Thus the critical synthetic 1,6-dihydropyridine precursor for the unique isoquinuclidine system of the iboga alkaloids, was generated by reduction of a pyridinium salt with sodium borohydride in base (137-140). Lithium aluminum hydride reduction of phenylisoquinolinium and indole-3-ethylisoquinolinium salts gave enamines, which could be cyclized to the skeletons found in norcoralydine (141) and the yohimbane-type alkaloids (142,143). [Pg.327]

Derivatives of pyridine-3,5-dicarboxylic acid have been shown to undergo reaction with lithium aluminum hydride by attack on the pyridine ring to form 1,4-dihydropyridines.57,58 Presumably the decrease in electron-density at the ring carbon atoms due to these substituents causes the ring to be extremely susceptible to hydride attack. Similar results were obtained with 3,5-dicyanopyridine derivatives. Methyl nicotinate, however, underwent reaction with LAH with exclusive reduction of the ester function.57 Recently the 3,5-dicyanopyridines have been reported to give mixtures of 1,2- and 1,4-dihydropyridines on reduction with LAH or sodium boro-hydride.20 ... [Pg.66]

The di-trans isomer 206 was isolated from the products of the reaction of 190 with the bisphosphonium salt 205 in the presence of lithium ethoxide. The reaction of 207 (obtained by the oxidative coupling of 206, with dimethyl sulphate followed by reduction with sodium hydrosulphite) yielded the cyclic compound, containing the dihydropyridine nucleus, 208a. Lithium aluminium hydride reduction of 207 yielded... [Pg.159]

Sodium hydride reduction of quinoline in HMPA leads to a 2 3 mixture of 1,2-dihydroquinoline (82) and 1,4-dihydroquinoline (83) isolated as the A-methoxycarbonyl derivatives. In situ produced copper hydride reagents react with pyridinium species with high regioselectivity generating 1,4-dihydropyridine... [Pg.588]

Many achiral or chiral substituted and bridged 1,4-dihydropyridines have been prepared by a reduction of quaternary pyridium salts with sodium hydrosulphite as NADH models for enantioselective reduction of some prochiral substrates. A lithium aluminium hydride reduction of Af-acylenamines has also been observed " . [Pg.489]

The key intermediate 124 was prepared starting with tryptophyl bromide alkylation of 3-acetylpyridine, to give 128 in 95% yield (Fig. 37) [87]. Reduction of 128 with sodium dithionite under buffered (sodium bicarbonate) conditions lead to dihydropyridine 129, which could be cyclized to 130 upon treatment with methanolic HC1. Alternatively, 128 could be converted directly to 130 by sodium dithionite if the sodium bicarbonate was omitted. Oxidation with palladium on carbon produced pyridinium salt 131, which could then be reduced to 124 (as a mixture of isomers) upon reaction with sodium boro-hydride. Alternatively, direct reduction of 128 with sodium borohydride gave a mixture of compounds, from which cyclized derivative 132 could be isolated in 30% yield after column chromatography [88]. Reduction of 132 with lithium tri-f-butoxyaluminum hydride then gave 124 (once again as a mixture of isomers) in 90% yield. [Pg.130]

During the reduction sequence, NADH transfers a hydride from a prochiral centre on the dihydropyridine ring, and is itself oxidized to NAD+ (nicotinamide adenine dinucleotide) that contains a planar pyridinium ring. In the oxidation sequence, NAD+ is reduced to NADH by acquiring hydride to an enantiotopic face of the planar ring. The reactions are completely stereospecific. [Pg.98]

The mechanism of 1,4-dihydropyridine reductions is actively being pursued (B-78MI20702). A mechanism involving hydride transfer is attractive because of its simplicity (80JA4198). However, many workers in the area prefer an electron transfer as the first step (79JA7402). The hydride mechanism can be completed by the transfer of a proton followed by an electron or by the transfer of a hydrogen atom (Scheme 29). It is unlikely that the mechanistic question will be resolved in the near future. It may be that the mechanistic pathway that these reactions follow is very sensitive to both the structure of the dihydropyridine and the compound being reduced. [Pg.383]

Reviews on stoichiometric asymmetric syntheses M. M. Midland, Reductions with Chiral Boron Reagents, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 2, Chap. 2, Academic Press, New York, 1983 E. R. Grandbois, S. I. Howard, and J. D. Morrison, Reductions with Chiral Modifications of Lithium Aluminum Hydride, in J. D. Morrison, ed.. Asymmetric Synthesis, Vol. 2, Chap. 3, Academic Press, New York, 1983 Y. Inouye, J. Oda, and N. Baba, Reductions with Chiral Dihydropyridine Reagents, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 2, Chap. 4, Academic Press, New York, 1983 T. Oishi and T. Nakata, Acc. Chem. Res., 17, 338 (1984) G. Solladie, Addition of Chiral Nucleophiles to Aldehydes and Ketones, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 2, Chap. 6, Academic Press, New York, 1983 D. A. Evans, Stereoselective Alkylation Reactions of Chiral Metal Enolates, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 3, Chap. 1, Academic Press, New York, 1984. C. H. Heathcock, The Aldol Addition Reaction, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 3, Chap. 2, Academic Press, New York, 1984 K. A. Lutomski and A. I. Meyers, Asymmetric Synthesis via Chiral Oxazolines, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 3, Chap. [Pg.249]

Kanomata et al. carried out the reduction of iV-alkylpyridinium salt 168 via hydride transfer from diolate 169 to afford mainly the 1,4-dihydropyridine 170 (Equation 89) <1998AGE1410>. [Pg.80]

The catalytic, asymmetric hydrogenations of alkenes, ketones and imines are important transformations for the synthesis of chiral substrates. Organic dihydropyridine cofactors such as dihydronicotinamide adenine dinucleotide (NADH) are responsible for the enzyme-mediated asymmetric reductions of imines in living systems [86]. A biomimetic alternative to NADH is the Hantzsch dihydropyridine, 97. This simple compound has been an effective hydrogen source for the reductions of ketones and alkenes. A suitable catalyst is required to activate the substrate to hydride addition [87-89]. Recently, two groups have reported, independently, the use of 97 in the presence of a chiral phosphoric acid (68 or 98) catalyst for the asymmetric transfer hydrogenation of imines. [Pg.229]

MISCELLANEOUS REACTIONS OF DIHYDROPYRIDINES Additional tests for net hydride transfers initiated by single-electron transfer include the use of substrates in which such pathways would necessarily involve readily ring-opened cyclopropylmethyl or readily cyclized 5-hexenyl radicals. Products from these radical reactions are not formed in NAD+/ NADH dependent enzymic reductions or oxidations (Maclnnes et al., 1982, 1983 Laurie et al., 1986 Chung and Park, 1982). Such tests have also been applied in non-enzymic reductions. Thus cyclopropane rings in cyclopropyl 2-pyridyl ketones, or imines of formylcyclopropane (van Niel and Pandit, 1983, 1985 Meijer et al., 1984) survive Mg+2 catalysed reduction by BNAH or Hantzsch esters but are opened by treatment with tributylin hydride. [Pg.101]

The pyridinium salts have been shown to have electrophilic positions at the 2-, 4-, and 6-carbon atoms. Of these, the 2- and 6-positions should be the more positive because of the proximity to the quaternary nitrogen. From the ultraviolet absorption spectra of the reaction mixtures during the reduction and of the isolated products, it can be demonstrated that the predominant attack of the hydride ion from sodium borohydride occurs at these two positions.5,6 The 1,6-dihydro-pyridine (such as 5) formed from the reduction of a 1,3-disubstituted pyridinium ion appears to be stable toward further reduction, for a number of such compounds have been isolated from sodium borohydride reductions containing sufficient borohydride to complete the reduction to the tetrahydro-state.7"10 Since 1,4-dihydropyridines having a 3-substituent which is electron-withdrawing have also been... [Pg.47]

The formation of piperidines from the borohydride reduction of pyridine and picoline methiodides has been reported by Ferles.17 He assumed that this complete reduction arose from initial formation of the 1,4-dihydropyridine, and that the ratio of tetrahydropyridine to piperidine represented the ratio of attack of hydride at the 2-position to that at the 4-position. [Pg.52]

A very extensive investigation of the reaction of pyridine and lithium aluminum hydride has been made by Lansbury and Peterson.60-82 These authors found that an aged solution of LAH in pyridine possessed unusual and selective reductive properties. Ketones and aldehydes were reduced while carboxylic acids were not, and diaryl ketones were reduced more readily than dialkyl ketones. These distinctive properties were found to result from a dihydropyridine-aluminum complex formed by the reaction of LAH and pyridine. [Pg.67]

The reduction of pyridinium quaternary salts with LAH has been reported to yield dihydro- and tetrahydropyridines, depending upon the structure of the salt and the conditions of the reaction. Kuss and Karrer63 reported the formation of a 1,2-dihydropyridine from the reaction of 1,2,6-trimethyl-4-phenyl-3,5-diethoxycarbonylpyridinium methosulfate and lithium aluminum hydride in ether. Ferles64 indicated that 1,3-dimethylpyridinium iodide (46) gave exclusively l,3-dimethyl-l,2,5,6-tetrahydropyridine (47) on reaction with LAH in chloroform. [Pg.67]

Reduction of aromatic heterocyclic bases and their quaternary salts is of particular interest. Reduction of pyridine with lithium aluminum hydride gives the unstable 1,2-dihydro derivative,403 whereas sodium in 95% ethanol yields 1,4-dihydropyridine. The latter is readily hydrolyzed with the formation of glutaric dialdehyde.404 Reduction of pyridine and its homologs with sodium in butanol affords a mixture of saturated and unsaturated bases d3-piperideines are formed405 only from those pyridine homologs which possess alkyl groups in positions 3 and 4. Electrolytic reduction always gives a mixture of both bases.406 A3-Piperideines have been obtained by reduction with a mixture of lithium aluminum hydride and aluminum chloride.407... [Pg.226]

In the 1,4-dihydropyridine series, there has been much discussion on detailed mechanism. In a study of reduction of-cyanocinnamates with a 4,4-dideutero Hantzsch dihydropyridine, a product that was singly deuterated at only the benzylic position together with the oxidized pyridine product 503 was obtained. This seems to show that the mechanism involves hydride transfer from the 4-position of the 1,4-dihydropyridine followed by proton extraction from the nitrogen of the dihydropyridine <2000J(P2)1857>. [Pg.320]

From this survey we found that several proton acids catalyze the reduction of ketimines using Hantzsch dihydropyridine 2 as the hydride donor. With regard to the different acids tested diphenyl phosphate... [Pg.210]


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See also in sourсe #XX -- [ Pg.962 ]

See also in sourсe #XX -- [ Pg.962 ]




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