Unusual Oxidative Dealkylation of Certain 4-Alkyl-1,4-Dihydropyridines With MnO<sub>2</sub>/Bentonite Using Microwave Irradiation, in the Absence of Solvent (II)

Delgado, Francisco; Álvarez, C.; García, O.; Pénieres, Guillermo; Márquez, C.

doi:10.1080/00397919108055446

Cited by 59 publications

(9 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, in the case of oxidation of the 1,4-DHP with alkyl group at the 4-poition a mixture of dealkylated (major) and alkylated (minor) products were obtained (Table 1). This may be due to the stability of carbocation formed in aromatization of 4-benzyl and 4-isopropyl derivatives and the reaction proceeds through the ionic mechanism (Scheme 2), further confirmed by the isolation of benzyl alcohol ( 18) and all other 4-n-alkyl substituted reacants gave dealkylated product 3 (Table 1, Entries 16,17). If in these cases carbocation mechanism was applied then primary carbocation would be formed, not a stable carbocation, which led to development of another mechanism (Scheme 4) and formation of alkene.…”

Section: Resultsmentioning

confidence: 60%

Solid State Oxidative Aromatization of Hantzsch 1,4‐Dihydropyridines to Pyridines Using Iodobenzene Diacetate or Hydroxy(tosyloxy)iodobenzene

Kumar¹

2009

Chin. J. Chem.

View full text Add to dashboard Cite

show abstract

Section: Resultsmentioning

confidence: 60%

Solid State Oxidative Aromatization of Hantzsch 1,4‐Dihydropyridines to Pyridines Using Iodobenzene Diacetate or Hydroxy(tosyloxy)iodobenzene

Kumar¹

2009

Chin. J. Chem.

View full text Add to dashboard Cite

show abstract

“…The dealkylation noted above has ample precedence in other oxidative processes also, especially when 4-isopropyl-or 4-benzyl-substituted Hantzsch esters are used for oxidations. 10,17,18 Interestingly, oxidation of diethyl 4-(4-hydroxyphenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (17) 23 with 1 was accompanied by the nitration of the phenolic ring to give product 18 (Scheme 2). The nitration of 17 at the phenolic ring is not totally unexpected since Laszlo 19 has recently described the use of 1 as a nitrating agent for reactive arenes.…”

Section: Methodsmentioning

confidence: 98%

Bismuth Nitrate Pentahydrate: A Convenient Reagent for the Oxidation of Hantzsch 1,4-Dihydropyridines

Mashraqui

Karnik

1998

Synthesis

View full text Add to dashboard Cite

Bi(NO 3 ) 3 ·5 H 2 O (1), an inexpensive crystalline solid readily oxidises several 4-substituted Hantzsch 1,4-dihydropyridines in acetic acid medium at room temperature. The reaction conditions are mild, easy to execute and the isolated yields of the oxidised products are fair to excellent. However, oxidation of 4-isopropyl-1,4 DHP 16 with 1 afforded the dealkylated pyridine 9, whereas the oxidation of 4-(4-hydroxyphenyl) Hantzsch ester 17 was accompanied by the nitration at the phenolic ring to form 18 in good yield.Hantzsch 1,4-dihydropyridines (Hantzsch 1,4-DHP) have been extensively utilised as the analogs of NAD(P)H coenzymes to study the mechanism and synthetic potential of various redox processes. 1,2 In addition, several 1,4-DHP based drugs, such as Nifedipine and Niguldipine have been recognised as calcium entry blockers for the treatment of cardiovascular diseases. 3-5 Both during the redox processes 2 and in the course of drug metabolism, 3 1,4-DHP systems are oxidatively transformed into the corresponding pyridine derivatives. Furthermore, the oxidation of readily accessible Hantzsch 1,4-DHP constitutes by far the easiest method to obtain pyridine derivatives. As a consequence, newer and improved methods to effect the oxidation of 1,4-DHP systems continued to be investigated. 6-14 However, many of the reported oxidation procedures either suffer from the use of strong oxidants (HNO 3 , 5 CrO 3 , 6 KMnO 4 7 ), require severe conditions (S 8 , and Pd/C dehydrogenations 9 ) or need excess of the oxidants (CAN, 10 PCC 11 ). In connection with our interest in the chemistry of dihydropyridines and related systems, 15,16 we became interested in developing a milder and convenient method to effect 1,4-DHP to pyridine conversion. We now report that Bi(NO 3 ) 3 · 5 H 2 O (1), a commercially available, inexpensive, crystalline solid, serves as an excellent oxidant for a variety of 4-substituted Hantzsch 1,4-DHP systems as shown in the generalised Scheme 1. Our results are collected in the Table. Our initial attempts to effect the oxidation of the simple Hantzsch 1,4-DHP 2 20 (R = H, Table) as a test case with 1 in CH 3 OH, CH 3 CN, or CH 3 COCH 3 solvents at ambient or thermal conditions produced none or insignificant amount of the corresponding pyridine (9, entry 1). However, to our delight, the oxidation of 2 with a stoichiometric amount of 1 in acetic acid occurred smoothly at room temperature to afford the expected pyridine 9 in 75% isolated yield (quantitative conversion by TLC). The success of this reaction prompted us to study the oxidation of several 4-alkyl, aryl and alkenyl Hantzsch 1,4-DHP under the above conditions. All reactions were stirred at room temperature until the substrates were completely consumed. The crude products obtained upon extractive workup are purified by short silica gel column chromatography or crystallisation, and the isolated yields of the oxidised products are fair to excellent (50-90%). The unique role of acetic acid in promoting these oxidations may be tentatively attributed ...

show abstract

“…In previous papers, we described the use of a natural clay as acid catalyst in different organic reactions (3)(4)(5)(6). We present in this report the results obtained for the reaction of primary amines with acetonylacetone using infrared radiation and a natural clay as catalyst in absence of solvent, as a variation to the Paal-Knorr reaction.…”

mentioning

confidence: 86%

A New Strategy for the Synthesis of N-Substituted 2,5-Dimethylpyrroles in Heterogeneous Medium.

Pénieres¹,

Soto²,

Álvarez³

et al. 1998

Heterocyclic Communications

Self Cite

View full text Add to dashboard Cite

show abstract

Unusual Oxidative Dealkylation of Certain 4-Alkyl-1,4-Dihydropyridines With MnO₂/Bentonite Using Microwave Irradiation, in the Absence of Solvent (II)

Cited by 59 publications

References 7 publications

Solid State Oxidative Aromatization of Hantzsch 1,4‐Dihydropyridines to Pyridines Using Iodobenzene Diacetate or Hydroxy(tosyloxy)iodobenzene

Solid State Oxidative Aromatization of Hantzsch 1,4‐Dihydropyridines to Pyridines Using Iodobenzene Diacetate or Hydroxy(tosyloxy)iodobenzene

Bismuth Nitrate Pentahydrate: A Convenient Reagent for the Oxidation of Hantzsch 1,4-Dihydropyridines

A New Strategy for the Synthesis of N-Substituted 2,5-Dimethylpyrroles in Heterogeneous Medium.

Contact Info

Product

Resources

About

Unusual Oxidative Dealkylation of Certain 4-Alkyl-1,4-Dihydropyridines With MnO2/Bentonite Using Microwave Irradiation, in the Absence of Solvent (II)

Cited by 59 publications

References 7 publications

Solid State Oxidative Aromatization of Hantzsch 1,4‐Dihydropyridines to Pyridines Using Iodobenzene Diacetate or Hydroxy(tosyloxy)iodobenzene

Solid State Oxidative Aromatization of Hantzsch 1,4‐Dihydropyridines to Pyridines Using Iodobenzene Diacetate or Hydroxy(tosyloxy)iodobenzene

Bismuth Nitrate Pentahydrate: A Convenient Reagent for the Oxidation of Hantzsch 1,4-Dihydropyridines

A New Strategy for the Synthesis of N-Substituted 2,5-Dimethylpyrroles in Heterogeneous Medium.

Contact Info

Product

Resources

About

Unusual Oxidative Dealkylation of Certain 4-Alkyl-1,4-Dihydropyridines With MnO₂/Bentonite Using Microwave Irradiation, in the Absence of Solvent (II)