Roy M. Letcher
Imperial College London
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Featured researches published by Roy M. Letcher.
Journal of The Chemical Society-perkin Transactions 1 | 1973
Roy M. Letcher; Llewellyn R. M. Nhamo
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.
Journal of The Chemical Society-perkin Transactions 1 | 1978
Roy M. Letcher; Kum-Moon Wong
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.
Journal of The Chemical Society-perkin Transactions 1 | 1992
Roy M. Letcher; Nai-Chiu Kwok; Kung-Kai Cheung
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.
Journal of The Chemical Society-perkin Transactions 1 | 1973
Roy M. Letcher; Llewellyn R. M. Nhamo
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.
Journal of The Chemical Society-perkin Transactions 1 | 1993
Roy M. Letcher; Della W.M. Sin; Kung-Kai Cheung
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.
Journal of The Chemical Society-perkin Transactions 1 | 1983
Roy M. Letcher; Michael C. K. Choi; R. Morrin Acheson
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.
Journal of The Chemical Society-perkin Transactions 1 | 1983
Roy M. Letcher; Michael C. K. Choi; R. Morrin Acheson; Richard J. Prince
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.
Journal of The Chemical Society-perkin Transactions 1 | 1973
Derek H. R. Barton; Abeysinghe A. L. Gunatilaka; Roy M. Letcher; Awa M. F. T. Lobo; David A. Widdowson
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.
Journal of The Chemical Society-perkin Transactions 1 | 1977
Roy M. Letcher; Kum-Moon Wong
Evidence for the non-regiospecific nature of the photocyclisation of certain 2-iodostilbenes to phenanthrenes is presented.
Journal of The Chemical Society-perkin Transactions 1 | 1998
Roy M. Letcher; Tai-Yuen Yue; Kwei-Fung Chiu; Avijit S. Kelkar; Kung-Kai Cheung
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.