A new synthesis of thiophenes

Tilak, B. D.; Desai, H. S.; Gupte, S. S.

doi:10.1016/0040-4039(64)83060-4

Cited by 22 publications

(8 citation statements)

References 4 publications

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“…To test the feasibility of the proposed benzannulation strategy, we selected ethyl acetoacetate, 1a ; benzylamine, 2a ; and ( E )-3-(4-methoxyphenyl)-1-phenylprop-2-en-1-one, 3a as the model substrates (Table 1). A mixture of 1a (0.42 mmol), 2a (0.46 mmol), and 3a (0.42 mmol) was heated in methanol at 65 °C in the presence of 10 mol % Ca(OTf) 2 /Bu 4 NPF 6 for 2 h (formation of hexadienyl amine, 3 1 d , was observed by thin-layer chromatography (TLC)) and then chloranil (1 equiv) was added to the reaction for oxidative aromatization 13 and the reflux continued for 12 h to isolate the proposed N -benzyl ethyl anthranilate ( 4a ) in 53% yield (entry 1, Table 1). 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone was also used for the oxidative aromatization, but it was not effective, probably the reaction was solvent free.…”

Section: Resultsmentioning

confidence: 99%

Amine-Triggered Highly Facile Oxidative Benzannulation Reaction for the Synthesis of Anthranilates under Solvent-Free Calcium(II) Catalysis

Yaragorla

Dada

2017

ACS Omega

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An amine-triggered facile synthetic approach of anthranilates has been described through benzannulation of readily available chemicals under one-pot solvent-free conditions using Ca(OTf) 2 as the sustainable catalyst. In this regioselective approach, we described a reasonably longer cascade, which proceeds through β-enamino ester formation/Michael addition/intramolecular aldol reaction/elimination/aromatization/oxidative debenzylation/lactonization with a broad substrate scope and high yields. The isolation of intermediates authenticated the mechanism, and the synthetic utility of the products was also demonstrated.

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Section: Resultsmentioning

confidence: 99%

Amine-Triggered Highly Facile Oxidative Benzannulation Reaction for the Synthesis of Anthranilates under Solvent-Free Calcium(II) Catalysis

Yaragorla

Dada

2017

ACS Omega

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“…In the fractional recrystallization the NO-diacetyl derivative ( 9 ) , if any was formed, crystallized out first, and then the O-acetyl derivative (8). Acetic anhydride (2 ml) was added to a solution of the 3-hydroxytetrahydrothiophen derivative (6) (0.01 mol) in pyridine (20 ml) and the mixture was worked up as in Method A.…”

Section: -Methodsmentioning

confidence: 99%

“…General Procedures for the Preparation of A cetyltetrahydrothiophens ( 8 ) and (9).--Method C . Acetic anhydride (4 ml) was added to a solution of the ketone (4) (0.01 mol) in pyridine (20 ml).…”

Section: -48mentioning

confidence: 99%

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Benzazoles. Part 12. Synthesis of 2-(tetrahydro-2-thienyl)benzimidazoles and their unsaturated derivatives by the reaction of 2-mercaptoalkylbenzimidazoles with β-electrophilic ketones

Hankovszky¹,

Hideg²,

Lex³

et al. 1980

J. Chem. Soc., Perkin Trans. 1

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2-(ar-Mercaptoalkyl) benzimidazoles (3) reacted with P-halogenoalkylketones (1 ) or with a,P-unsaturated ketones (2) to form the vinylogue adducts (4) which cyclised to give 2-(3-hydroxytetrahydro-2-thienyl) benzimidazoles (6). Compounds (4) or (6) reacted with acetic anhydride at room temperature to give the mono-(8) and diacetylated (9) derivatives of (6). At higher temperature dehydroacetylation occurs to give 2-(2,3-dihydro-Zthienyl) benzimidazoles (1 1 ).IT had been found earlier that the carbonyl group of 3-(2thiobenzimidazolyl)propiophenone, which is formed in the reaction of 2-mercaptobenzimidazole with p-chloropropiophenone, does not react with the nitrogen of the benzimidazole, and that ringclosure with the benzimidazole-NH can be carried out only by the reduction of the ketone group to a hydroxy-group which is, in turn, converted into a halogen atom.2 However, it is known that 2-mercaptobenzimidazole reacts with a-halogenoketones to form 3-hydroxy-2,3di h ydrot hiazolo '3, %a] benzimidazoles which exist in equilibrium with their open-chain aminoLketone tauto-me1-5.~ The reaction of 2-(mercaptomethy1)benzimidazole (3a) with p-halogenoketones (la,b) gave the products (4a,b),4*5 but the workers claimed that the ring-closure gave a thiazepinobenzimidazole compound (5) as a result of a reaction between the irnidazole nitrogen and the carbonyl group when the ketones (4a,b) were heated in polyphosphoric acid, and mention that an attempted ring-closure by heating the ketones (4a,b) in pyridine-acetic anhydride failed.4g5When (3a) reacted with either the p-halogenoketones (la,b) or the a,P-unsaturated ketones (2a,b) the saturated ketones (4a,b) which are formed are partially cyclized at room temperature in a few hours to give 2-(3-hydroxytetrahydro-2-thieny1)benzimidazoles (6a,b) instead of the thiazepinobenzimidazoles (5).The nearest analogues to this ring-closure reaction 6 9 7 are the reactions of ethyl thioglycolate with a,p-unsaturated ketones which afforded 2-ethoxycarbonyl-3-hydroxytetrahydrothiophens or those of ethyl thioglycolate with p-chlorovinyl ketones lo or aldehydes l1 yielding 2-ethoxycarbonylthiophens. The 2 -(2-thienyl)benzimidazoles have been hitherto prepared from o-phenylenediamine and thiophencarbaldehydes l2 by the Weidenhagen met hod. l3Since the ring-closure reaction of (4a,b) is a Knoevenagel-type reaction which occurs between the carbonyl and the active methylene groups (route b) and takes place in a good yield at room temperature and no formation of (5) (route a) was observed, the reaction was investigated in detail. RESULTS AND DISCUSSIONWhen the saturated ketone (4) was heated under reflux in chloroform-acetone (1 : 1) in the presence of piperidine, this proved to be suitable for the preparation for a wide range of 2-(3-hydroxytetrahydro-2-thienyl)benzimidazoles (6). Different ketones (4a-j) reacted at different rates. The ring-closure reaction always took place more readily when R5 = H than when R5 = Me. When R4 = H the cyclization is significantly quicker.The ring-closure in ace...

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“…During peptide synthesis the phenolic function of tyrosine is usually protected in order to prevent undersirable side chain branching at this site (e.g., Merrifield & Erickson, 1973). Such masking is of great value in multistep syntheses and particularly in processes where an excess of acylating reagents is being used for chain elongation (Merrifield, 1963;Fridkin et ul., 1966;Tilak, 1970;Hirschmann et ul., 1971). A useful 0-protecting group should be readily available; stable during synthetic operations, such as the removal of N-or Cprotecting groups and during purification procedures; and selectively removable under mild conditions which do not affect the amino acids of the peptide chain or labile amide bonds.…”

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A Photolabile Protecting Group for the Phenolic Hydroxyl Function of Tyrosine

Amit

Hazum

Fridkin

et al. 1977

International Journal of Peptide and Protein Research

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The ortho‐nitrobenzyl group (ONBzl) was utilized to protect the phenolic function of the side chain of tyrosine. Optimal conditions for its mild photolytic removal were established. This paper describes the preparation and properties of some (O‐ONBzl)‐tyrosine derivatives of potential value in the synthesis of tyrosine‐containing peptides. Their use in the synthesis of the dipeptide, N‐benzyloxycarbonyl‐L‐tyrosyl‐glycine ethyl ester is presented as an example.

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A new synthesis of thiophenes

Cited by 22 publications

References 4 publications

Amine-Triggered Highly Facile Oxidative Benzannulation Reaction for the Synthesis of Anthranilates under Solvent-Free Calcium(II) Catalysis

Amine-Triggered Highly Facile Oxidative Benzannulation Reaction for the Synthesis of Anthranilates under Solvent-Free Calcium(II) Catalysis

Benzazoles. Part 12. Synthesis of 2-(tetrahydro-2-thienyl)benzimidazoles and their unsaturated derivatives by the reaction of 2-mercaptoalkylbenzimidazoles with β-electrophilic ketones

A Photolabile Protecting Group for the Phenolic Hydroxyl Function of Tyrosine

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