Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where Roy M. Letcher is active.

Publication


Featured researches published by Roy M. Letcher.


Journal of The Chemical Society-perkin Transactions 1 | 1973

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

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

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

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

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

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

Structure of orchinol, loroglossol, and hircinol

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

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

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

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

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

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

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

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

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

Photochemical cyclisation of 2-iodostilbenes

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

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

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.

Collaboration


Dive into the Roy M. Letcher's collaboration.

Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar

Thomas C. W. Mak

The Chinese University of Hong Kong

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Researchain Logo
Decentralizing Knowledge