Repost from my harddrive:
One of the most interesting (i.e. cheap and easy) routes to 4-OH-indole is the ammonolysis of 4-oxo-4,5,6,7-tetrahydrobenzofurane (4-OTHB) to 4-oxo-4,5,6,7-tetrahydroindole (4-OTHI) and subsequent dehydrogenation. Here's a list of papers:
4-OTHI from 4-OTHB:
Heterocycles 22, 2313 1984 M. Matsumoto e.a.: one of the most interesting papers, 4-OTHB from 1,3-cyclohexanedione and chloroacetaldehyde.
CA 101, 23319d 1984 (EP 101,003) M. Matsumoto e.a.: the corresponding patent for 4-OTHB preparation(download the patent).
CA 101, 23331b 1984 (EP 101,004) M. Matsumoto e.a.: the corresponding patent for 4-OTHI preparation (download the patent).
CA 104: 148736f (JP 60,228,457) + 148737g (JP 60,228,456) +148738h (JP 60,228,455) 1986 K. Goto e.a.: ammonolysis in H2O, purification.
CA 106, 67111n (JP 61,180,768) + 67112p (JP 61,180,767) 1987 S. Matsuno e.a.:
4-OTHB ammonolysis in polyol partial ethers, dehydrogenation, purification.
4-OTHI from different routes:
Ann. Chem. 655, 20 1962 H. Stetter e.a.: 4-OTHI from 2-acetonyl-1,3-cyclohexanedione.
Tet. Lett. 37, 9203 1996 Y. Aoyagi e.a.: 4-OTHI from 1,3-cyclohexanedione, 2-amino-ethanol, and catalyst.
CA 102, 62078q 1985 (JP 59,144,758) Ube Industries: 4-OTHI from 1,3-cyclohexanedione, 2-amino-ethanol, and catalyst.
Recl. Trav. Chim. Pays-Bas 109, 287 1990 E. M. M. van den Berg e.a.: 4-OH-indole from 4-OTHI from 4-OTHB-3-carboxylic acid (with ammonium carbonate) from 1,3-cyclohexanedione and ethyl bromo pyruvate.
CA 101, 7022w 1984 (JP 59 05,159): 4-OTHI from 4-OTHB-3-carboxylic acid with ammonium salts.
Synth.Commun. 16, 1635 1986 Kneen e.a.: 4-OTHB-3-carboxylic acid from 1,3-cyclohexanedione and bromo pyruvate or bromoacetaldehyde diethylacetal.
Chem. Lett. 1603 1980 S. Torii: 4-OTHI from cyclohexanedione and ethyl vinyl ether via electrolysis and ammonolysis with ammonium carbonate.
CA 108, 94379d 1988 (JP 62,138,469) K. Nagao e.a.: 4-OTHI from 1,3-cyclohexandione + NH3 / H2O + acetic acid 1,2-dibromoethyl ester.
CA 71, 81163w 1969 M. Julia: 4-OTHI from 4-(2-pyrrolyl)-butyric acid.
J. Chem. Soc. Perk. I 1237 1974 A. G. Sánchez: 4-OTHI from 1,3-cyclohexanedione and aminosugars.
Chem. Commun. 1429 1968 J. M. Bobbitt e.a.: 4-OTHI from 1,3-cyclohexanedione and aminoacetaldehyde dimethylacetal.
J. Org. Chem 43, 3541 1978 M. Bobbitt: 4-OTHB from 1,3-cyclohexanedione and aminoacetaldehyde dimethyl acetal.
Chim.Ther. 5; 279 1970 Julia e.a.: 4-OTHI preparation.
Dokl. Chem.(Engl.Transl.) 171, 1191 1966 Yurchenko e.a.: 4-OTHI preparation.
4-OH-indole from 4-OTHI dehydrogenation:
J. Het. Chem. 14, 71 1977 D. B. Repke: dehydrogenation, synthesis of 4-OH-tryptamines.
J. Org. Chem. 36, 1232 1971 W. A. Remers e.a.: dehydrogenation + some references.
CA 103, 215269t 1985 (JP 60,152,462) H. Fukumitsu e.a.: dehydrogenation.
CA 107, 236506y 1987 (JP 62 63,563) Nagao e.a.: dehydrogenation.
Chem. Ber. 101, 2605 1968 H. Plieninger e.a.: dehydrogenation.
Heterocycles 23, 165 1985 M. Matsumoto e.a.: aromatization via halogenation with CuX2 and dehydrohalogenation with Li2CO3 + LiX in DMF.
Here are some other interesting articles for alternative 4-OH-indole syntheses:
J. Het. Chem. 19, 845 1982 D. B. Repke e.a.: 4-AcO-indole to many 4-OH-tryptamines via glyoxylamides.
J. Het. Chem. 18, 175 1981 D. B. Repke e.a.: synthesis of 4-MeO-indole, reaction with 1-dimethylamino-2-nitroethylene, LAH reduction to tryptamines.
Synth. 437 1985 S. Andersson: a high yield PTC phenolether cleavage procedure! Many substrates! A must!
Heterocycles 16, 1119 1981 L. I. Kruse: synthesis of 4-NH2 / COOCH3 / CH3 / OH / MeO / BnO-indoles.
Heterocycles 22, 797 1984 M. Somei: 4-OH-indole-3-carbaldehyde from indole-3-carbaldehyde via 4-thallium-bistrifluoroacetate.
Chem. Pharm. Bull. 29, 3145 1981 M. Somei e.a.: 4-OH-indole from 4-aminoindole from 4-nitroindole from 2,6-dinitrotoluene.
Org. Synth. Coll. Vol. VIII, 493 1993 J. Bergmann: 4-nitroindole from 2-methyl-3-nitroaniline.
Tet. Lett. 24, 3665 1983 J. Bergmann: 4-nitroindole from 2,6-dinitrotoluene.
Chem. Pharm. Bull. 29, 726 1981 M. Somei e.a.: 4-subst. Indoles, 4-aminoindole from indole (!).