Roy M. Letcher

Chemical constituents of the combretaceae. Part IV. Phenanthrene derivatives from the heartwood of Combretum hereroense

Two new compounds, shown to be 3,6-dihydroxy-2,4,7-trimethoxyphenanthrene and its 9,10-dihydro-derivative, have been isolated from the heartwood of Combretum hereroense.

Structure and synthesis of the phenanthrenes Tal and TaV from Tamus communis

Using photochemical syntheses, the structure of TaV has been confirmed as 2,5,6,7-tetramethoxy-1-phenanthrol, and the structure of Tal revised to 1,2-methylenedioxy-5,6,7-trimethoxyphenanthrene. The influence of certain substituents at C-4 on the chemical shift of the C-5 proton in phenanthrenes is demonstrated.

First synthesis of spiro[benzofuran-2,1′-isobenzofuran]-3,3′-dione and its X-ray crystal structure

The title compound has been synthesised by selenium dioxide oxidation of 2′-carboxy-2-hydroxy-deoxybenzoin 3 and its structure has been confirmed spectroscopically and by X-ray crystallography. An earlier report of this compounds synthesis is shown to be erroneous. The synthesis of 3-(2-hydroxyphenyl)isoquinolin-1 (2H)-ones from 2′-carboxy-2-hydroxydeoxybenzoin 3 is also described.

Structure of orchinol, loroglossol, and hircinol

The proposed structures of orchinol and loroglossol (9,10-dihydro-2,4-dimethoxy-5- and 7-phenanthrol, respectively) are confirmed by syntheses, and hircinol is shown to be 9,10-dihydro-4-methoxyphenanthrene-2,5-diol.

Oxazolo[3,2-a]indoles, pyrrolo- and azepino-[1,2-a]indoles from 3H-indole 1-oxides and acetylenecarboxylic esters by skeletal rearrangements

3H-Indole N-oxides 3 have been prepared from 3H-indoles 1 by hydride reduction followed by mchloroperbenzoic acid oxidation. Reaction of 3 with dimethyl acetylenedicarboxylate (DMAD) and with methyl propiolate (MP), give a variety of products, all apparently formed by rearrangement of the initial isoxazole 1,3-dipolar cycloadduct, with the type of reaction being dependent on the 2substituent in 3: the 2-phenyl derivative of 3 gives oxazolo[3,2-a]indoles 5, and when 3 posseses a methyl or methylene substituent at C-2, both DMAD and MP give pyrrolo[1,2-a]indoles 6, with the MP reactions also yielding an azepino[1,2-a]indole 7 in each case. The structures of the products have been established by spectroscopy with those of 5b and 7b being confirmed by X-ray crystallography.

Addition reactions of heterocyclic compounds. Part 79. Reaction of dimethyl acetylenedicarboxylate with some cyclohept[b]indoles and cyclo-oct[b]indoles

The reactions of dimethyl acetylenedicarboxylate with N-methyl- and pyrido[3,2,1-hi]indoles which have either a penta- or hexa-methylene chain linking positions 2 and 3, have been found to give rise to a very similar array of products. Nineteen new adducts were isolated and their structures established by 1H and 13C n.m.r. spectral comparisons, and in some cases also by chemical transformations. The structures include five new classes of adducts not previously encountered: two types of (1 + 1 DMAD) adducts, one of which is a cyclobutene and the other a 3-maleate; two types of (1 + 2 DMAD) adducts, one with two side chains, and the other having a ring-expanded nine- or ten-membered ring and one side chain; and a (1 + 2 DMAD - CH4O) adduct, all examples of which exhibit fragmentation on heating to give a carbazole and a spiro-cycloalkyl-keten dimer. The isolation of the two (1 + 1 DMAD) adducts is important as both adduct types have been postulated as intermediates in the formation of more complex adducts.

Addition reactions of heterocyclic compounds. Part 77. Reaction of dimethyl acetylenedicarboxylate with 2- and 3-alkyl substituted indoles and the formation of (1 + 1 DMAD–CH4O) adducts

Dimethyl acetylenedicarboxylate (DMAD) adds to 1,3-dimethylindole in moist acetic acid to give 2-substituted adducts. The dienone formulation for a product from 1,2,3-trimethylindole and DMAD has been confirmed by making use of proton-coupled 13C n.m.r. spectra. The generality of the formation of this (1 + 1 DMAD-CH4O) adduct is shown by the preparation of a further five new dienones including two bicyclo[9,3,1]pentadecadienones.

Phenol oxidation and biosynthesis. Part XXII. The alkaloids of Erythrina lysistemon, E. abyssinica, E. poeppigiana, E. fusca, and E. Lithosperma; the structure of erythratidine

Erythrina lysistemon, E. abyssinica, E. poeppigiana, E. fusca, and E. lithosperma have been examined for alkaloids of biogenetic interest. In addition to the known Erythrina alkaloids, α- and β-erythroidine, eryosdine, erythraline. erythratine, and erysotrine, new alkaloids erythristemine. erythratidinone, and 3-demethoxyerythratidinone were isolated and characterised. The aporphine alkaloid isoboldine, and the benzyltetrahydroisoquinoline alkaloids (–)-orientaline and (+)-N-nororientaline were also isolated. A partial synthesis of erythratidine indicated a 2S configuration. A plausible biogenetic scheme for the new alkaloids is discussed.

Photochemical cyclisation of 2-iodostilbenes

Evidence for the non-regiospecific nature of the photocyclisation of certain 2-iodostilbenes to phenanthrenes is presented.

The synthesis of various cycloalkana[d]xanthones and conversion of the cyclohexa-analogue to a 7,7a-dimethylcyclohexa[d]xanthene†

The synthesis of cyclo-penta-, -hexa- and -hepta-[d]xanthones 5 from (E)-(2-hydroxyphenyl)-5-arylpent-4-ene-1,3-diones 4, cycloalkanones and pyrrolidine is described. Reactions to modify 5 in an attempt to synthesize analogues of the five naturally occurring cyclohexa[d]xanthenes (with general formula 1) are also described: these reactions include C-methylations at C-7 and C-7a, hydride reduction of the 8-keto group, dehydroxylations and finally catalytic reduction to give 16. The stereochemistry of 16 established by NOE and an X-ray crystal structure of 9aB differs from 1 at two contiguous C-atoms.