165928a0Nature1654206195006109289280028-0836195010.1038/165928a0ukNatureNatureNATUREnatureNature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public./nature/journal/v165/n4206issueJournal homeArchiveCurrent issueAdvance online publicationPrivacy policySubscribeNature Publishing GroupCurrent issue165928a0Revision of Structural Interpretations among Tetrahydrocarbazole Derivatives
AU  - PLANT, S. G. P.
AU  - ROBINSON, R.
AU  - TOMLINSON, M.Dyson Perrins Laboratory, University, Oxford. March 8.IT has already been reported1 that the action of acids on 9-acetyl-10 : 11-dihydroxyhexahydrocarbazole yields an oxindole instead of a pseudo-indoxyl derivative, and this was confirmed by the synthesis of the latter, found to be identical with the so-called /`11-hydroxytetrahydrocarbazolenine/'.Mr. L. J. Goldsworthy has now directly compared Bucherer's product2 (m.p. 151) from the dehydration of anilino-fcsobutyric acid with dimethyloxindole prepared from ^sobutyrophenylhydrazide3 and found the specimens to be identical, as was surmised in our previous note. Independently and simultaneously, these revisions have also been proposed by Witkop4. It is necessary, therefore, to state some further conclusions which have been experimentally confirmed.
The action of bromine, followed by that of water, on 9-benzoyltetrahydrocarbazole5 was found to produce a substance which is now considered to be 9-benzoyl-l-hydroxytetrahydrocarbazole and which certainly yields 1-hydroxytetrahydrocarbazole (I) on hydrolysis. This compound (m.p. 115-116) was formerly regarded as ll-hydroxy-2 : 3 : 4 : 11-tetra-hydrocarbazole. Its true constitution is shown by the fact that it can be prepared along with 1-hydroxy-hexahydrocarbazole by the reduction of 1-ketotetra-hydrocarbazole with sodium and alcohol. This difficult reduction was first effected in this Laboratory by Mr. B. P. Moore.
On heating with acetic anhydride, and in other ways, 1-hydroxytetrahydrocarbazole suffers facile condensation to the so-called 'dihydrocarbazole' (m.p. 293-295, recently confirmed) (according to Patrick and Witkop6, m.p. 255 and 313 after resolidification). On account of its high melting point this substance has long been under suspicion, and the structure II is now attributed to it.
It was found in 1933 7 that on heating with sulphur it yielded no carbazole but a compound that crystal, lized in greenish-yellow needles (m.p. 337), and exhibited a brilliant violet fluorescence in benzene solution (found : C, 87-6; H, 4-5 per cent).
L l^_
NH OH
That 'dihydrocarbazole' is derived from two molecules of tetrahydrocarbazole has also been recognized by Patrick and Witkop (loo. cit.); but the formula given, namely, C^HjgNa, is a misprint and should be C24H22N2. The dehydrogenation product mentioned above was stated7 to be C24H14]Sr2 (requires C, 87-3; H, 4 "2 per cent) and it is (II) in which rings (A) and (B) are benzenoid. The hydroxyl in (I) may be derived by direct replacement of a bromine atom, but it is also possible that it results from an a-y anionoid rearrangement.
The bromination of tetrahydrocarbazole itself afforded an isomeride of (I) which was considered to be 10-hydroxy-l : 2 : 3 : 10-tetrahydrocarbazole8.
This substance (m.p. 153) is actually the true 11-hydroxytetrahydrocarbazolenine (cf. Patrick and Witkop, loc. cit.), and on treatment with nitrous acid and coupling of the resultant diazonium salt with 2-naphthol, it yields an azo-compound (m.p. 143), which gives analytical results agreeing with, the formula CaaHgoOa^, and not C22H18O2N2.
The above conclusions have been confirmed by a comparison of ultra-violet absorption spectra of the relevant substances and appropriate models.Plant and Robinson, Nature, 165, 36 (1950).ArticlePubMedISIChemPortBucherer and Grolee, Ber. deut. chem. Ges., 39, 991 (1906).Plancher and Bettinalli, Gazetta, 29, 1, 115 (1899).Witkop, J. Amer. Chem. Soc., 72, 614 (1950).ArticleISIChemPortPlant and Tomlinson, J. Chem. Soc., 3324 (1931).Patrick and Witkop, J. Amer. Chem. Soc., 72, 634 (1950).Tomlinson, , MissM., D.Phil. Thesis, Oxford University (1933).Plant and Tomlinson, J. Chem. Soc., 298 (1933).