Methoxynaphthaldehydes as constituents of the heartwood of Diospyros quiloensis and their synthesis by the Stobbe condensation

Abstract

Seven compounds, five of them new, have been isolated from the heartwood of Diospyros guiloensis. The new compounds have been shown by chemical and spectroscopic methods, and by synthesis, to be 4, 5,6,8-tetramethoxy-, 5-hydroxy-4,6,8-trimethoxy-, 4,5,8-trimethoxy-, 4,5-dimethoxy-, and 5-hydroxy-4-methoxy-2-naphthaldehyde. The other two, 4.5.6-trimethoxy-and 6-hydroxy-4,5-dimethoxy-2-naphthaldehyde, have been isolated previously from a Diospyros species.Related methoxynaphthoic acids and methoxynaphthaldehydes have been synthesised by Stobbe condensation and cyclisation. The structures of the compounds derived by cyclisation of the mono-and bis-condensation products of 3.4-dimethoxybenzaldehyde with ethyl succinate have been determined on the basis of spectral considerations and explained on stereochemical grounds.The n.m.r. spectra of these substituted naphthoic acids and naphthaldehydes confirm the importance of the peri-effect and the large deshielding by an 8-methoxy-group on a proton in the 1 -position.THE EBENACEAE is one of the smaller families of flowering plants, having only three genera; of these, Diospyros is by far the largest, with about 500 species.l The family is widespread in the tropics and 18 species occur in Rhodesia, of which 12 belong to the genus Dio~pyros.~ Chemical examination of the Ebenaceae has been mainly confined to the Diosfiyros genus, naphthoquinones and other naphthalene derivatives have been i ~l a t e d . ~ Our interest in this genus was aroused because of reports of the use of the fruits of some species as fish poisons; several species are termite resistent, and compounds toxic 1

Antioxidant and cytotoxic activities of naphthalene derivatives from Diospyros kaki

“…1 A unique feature of the Diospyros genus is the presence of a large number of naphthalene derivatives. Several naphthaldehydes have been isolated from Diospyros spp., 2,3 and some naphthoquinones were isolated from six species of the genus Diospyros in Japan and their antifungal activities were investigated. 4 Ganapaty et al 5 showed that naphthalene derivatives obtained from Diospyros assimilis exhibited moderate inhibitory effects against protozoan parasites.…”

The Synthesis of Ventiloquinone F and Isoventiloquinone F as Racemates

“…The naphthalene oxygenation pattern of ventiloquinone F (7) directed our approach to Stobbe methodology and despite some elegant work by Sargent et al [13] on the use of phosphoranes [14] and McCombie et al [15] on the use of triphenylphosphane [15] as alternative methods, our experience [16] and some others [17,18] in this most classic of reactions, favoured the former approach.…”

The synthesis of ventiloquinone L, the monomer of cardinalin 3

“…The organic layer was then dried with MgSO 4 , filtered through Celite, the solvent removed in vacuo and the resultant oil purified by silica gel column chromatography (10% EtOAc-hexane) to afford the product 10 (4.75 g, 73%) as a colourless oil. 14 As described in the literature, 22,23 Stobbe condensation of 2,4-dimethoxybenzaldehyde followed by aromatic ring closure afforded the desired naphthalene 27. Removal of the acetate protecting group of 27 with guanidine hydrochloride and KOBu t yielded the desired intermediate naphthol in excellent yield.…”

“…Found M + 364. 22.0 (1-CH 3 ) and 21.9 (3-CH 3 );  max (film)/cm −1 3367br and 3172br (O-H), 2958w (C-H), 2852w (C-H), 1606m and 1574w (CC) and 1291s (C-O); m/z 364 (M + , 24%), 273 (18), 272 (12), 230 (21), 229 (100), 212 (10), 199 (7) and 91 (62).…”

“…The combined extracts were dried with MgSO 4 , filtered through Celite and the solvent removed in vacuo. Purification by column chromatography (30% EtOAc-hexane) followed by recrystallisation from EtOAc, gave ethyl 4-hydroxy-6,8-dimethoxynaphthalene-2-carboxylate 23 , d, J 1.1, 3-H), 7.06 (1H, d, J 2.0, 5-H), 6.66 (1H, d, J 2.0 7-H), 4.32 (2H, q, J 7.1, OCH 2 CH 3 ), 3.96 (3H, s, OCH 3 ), 3.89 (3H, s, OCH 3 ) and 1.34 (3H, t, J 7.1 OCH 2 CH 3 ); 13 (22), 205 (19), 175 (6), 145 (6), 115 (15), 91 (6), 69 (9) and 43 (13).…”