Synthesis of 5,6-Dimethoxyindoles and 5,6-Dimethoxyoxindoles. A New Synthesis of Indoles

Walker, Gordon N.

doi:10.1021/ja01619a049

Cited by 60 publications

(28 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The experimental procedure is very simple, convenient and also does not require any special precautions for the isolation of products. The alkylated products were converted to their corresponding Flurbiprofen and Oxindole by known methods in the literature [25][26][27][28].…”

Section: Resultsmentioning

confidence: 99%

Microwave Promoted Alkylation of Halonitrobenzene with Malonates in Solvent-free Medium

Akkirala

2007

Catal Lett

View full text Add to dashboard Cite

The alkylations on different substituted halonitro benzenes have been demonstrated with various malonates under the influence of microwaves irradiation. The reactions were catalyzed by potassium carbonate and benzyltriethylammoniumchloride. The salient features of this methodology are mild reaction conditions, high regioselectivity, rapid conversions, solvent-free medium and easy isolation of products

show abstract

Section: Resultsmentioning

confidence: 99%

Microwave Promoted Alkylation of Halonitrobenzene with Malonates in Solvent-free Medium

Akkirala

2007

Catal Lett

View full text Add to dashboard Cite

show abstract

“…Walker first used catalytic hydrogenation in the Pschorr-Hoppe indolization to prepare 5,6-dimethoxyindoles (Scheme 2, equations 2-4) [3]. Walker first used catalytic hydrogenation in the Pschorr-Hoppe indolization to prepare 5,6-dimethoxyindoles (Scheme 2, equations 2-4) [3].…”

Section: Pschorr-hoppe Indole Synthesismentioning

confidence: 99%

Pschorr–Hoppe Indole Synthesis

Gribble

2016

Indole Ring Synthesis

View full text Add to dashboard Cite

“…Interest in the reductive cyclization (209,241) of o-nitrophenylacetonitriles was reawakened by Walker (273) Walker suggested that "2-aminoindoles" were intermediates in the for mation of indole, but Snyder and co-workers (236) have rejected this mechanism on the basis of the observation that the 2-aminoindole D36 could not be converted to the indole D37 under conditions sufficient to form the latter from starting nitro compound D35.…”

Section: Reductive Cyclization Of O-nitrobenzyl Ketones and Cyanidesmentioning

confidence: 99%

Synthesis of the Indole Ring

1970

Organic Chemistry

View full text Add to dashboard Cite

H A8 H R NH 2 A7arrangements. One line of effort has involved attempts to detect or trap the intermediates proposed for the various steps in the reaction. The hydrazonevinylhydrazine equilibrium in the first step of the reaction is analogous to ketone-enol and imine-enamine equilibria, but no firm physical evidence for the existence of measurable concentrations of the vinylhydrazine has been found to date (25a, 137a, 182, 183).Refluxing the phenylhydrazone of methyl ethyl ketone in acetic anhydride gives the diacylated vinylhydrazine A10. This can be considered to consti tute t r a p p i n g " of the first intermediate in the Fischer cyclization. Heating A9 /Et + Ac 2 0 H "Me H+ A10 A13 H NHAc A12 Me A14 H Ac 1 N / N v y A M e Ac I Me OH Me Ac H Me a V^M e NHAc NH 2 Me All D HI. SYNTHESIS OF THE INDOLE RINGA10 with dilute mineral acids gives 2,3-dimethylindole (259). These trans formations appear to constitute the closest analogy observed to date for the first step in the Robinson mechanism. Alkaline hydrolysis of A10 gave a substance formulated as A l l (259). This material gave 2,3-dimethylindole and acetamide on heating. Reexamination (72a) of the structure of this material has shown that it is actually A12. The formation of A l l can no longer be cited as an analogy for the second stage of the Robinson mechan ism. There are, however, products formed during Fischer reactions in certain cyclic systems which correspond to interruption of the reaction after the ortho substitution step. Plieninger (203,206) has reported the isolation of A16 by treatment of A15 with hydrochloric acid in acetic acid. Subsequent nmr spectral evi dence (185) has shown that the substance actually exists as the tautomer A17. It has been suggested that A17 is isolated because the enamine is very weakly basic and therefore the iminium species A18 is not generated in sufficient concentration to lead to indolization (185).Southwick and co-workers (238) have recorded isolation of compounds of structure A21. Structure A21 corresponds to interruption of the normal Fischer sequence at the aromatization stage. It has been suggested that ring A. THE FISCHER INDOLE SYNTHESIS □ 145 A20 N -I^< N R H ΝΗ 2^Ό A21 NH 3 R •N : NR A22 O strain effects are responsible for the failure of A21 to lose ammonia. Ring C of structure A22 contains three sp 2 atoms, representing considerable angle strain. Carlin and co-workers have examined the behavior of 2,6-disubstituted arylhydrazones under conditions of the Fischer synthesis (51, 54, 57, 59). Diortho substitution prevents the tautomerization A6 -> A7 in the Robinson mechanism. Heating the 2,6-dimethylphenylhydrazone of acetophenone in the presence of zinc chloride gives as the main product A24, as well as 4,7-dimethyl-2-phenylindole and cleavage products (54). The intermediate A26 can account for the formation of A24 and A25. / M e / V-NH-N < Ph Me Me A23The key step in the formation of the atomic skeleton of A24 is the trans formation A26 -> A29 which is analogous to a nucleophilic addition to a cyclohexadien...

show abstract

Synthesis of 5,6-Dimethoxyindoles and 5,6-Dimethoxyoxindoles. A New Synthesis of Indoles

Cited by 60 publications

References 0 publications

Microwave Promoted Alkylation of Halonitrobenzene with Malonates in Solvent-free Medium

Microwave Promoted Alkylation of Halonitrobenzene with Malonates in Solvent-free Medium

Pschorr–Hoppe Indole Synthesis

Synthesis of the Indole Ring

Contact Info

Product

Resources

About