Sodium naphthalenide-induced conversion of 3-methoxycarbonyl-4-oxo-4<I>H</I>-1-benzopyran into 4-hydroxy-3-salicyloylxanthone

Abstract

In recent years, the synthesis of xanthone derivatives has attracted special attention due to their many biological activities specially as antitumour agents 1 A small liophilic substituent at the C-5 position of xanthone-4-acetic acid enhances the dose potency as an antitumour agent. 2 The antibiotic bikaverin, 3,4 which contains benzo [b]xanthone skeleton, has a high vacuolation property and is a fungal metabolite. Recently, a number of glycosides linked at the 2-position to 4, 5, 8-trimethoxyxanthone have been isolated from ethanolic solution of rhizome of A. Calamus. 5 In view of the natural occurrence and useful range of biological activity associated with the xanthone moiety, various methods have been developed for their syntheses. Most syntheses have been carried out from benzene derivatives and a few from benzopyran-4-ones. 6 We intended to couple 3-functionalised 4-oxo-4H-1benzopyrans through their 2-positions. This coupled product could serve as a precursor for many oxygenerated polycyclic compounds. We have recently reported 7 that 3formylchromenone 1 fails to produce the desired coupled product when treated with sodium naphthalenide or zinc. Product formation was rationalised by considering the initial addition of electron to the aldehyde function of 1 rather at C-2 of the chromenone moiety. Treatment acetal 2 of sodium naphthalenide produced the same mixture of products as was obtained from 1. An earlier report 8 showed that reactions of nucleophiles either with 1 or with 2 produce the same products. Reaction of sodium naphthalenide with ketone 3 produced 2-salicyloylxanthone as was obtained from base-catalysed transformation of 3. 9 Hydrodimerisation of α, β-unsaturated esters 10 by SmI 2 , cyclodimerisation of α, β-unsaturated esters to cyclopentanone derivatives by Yb 11 or by sodium naphthalenide 12 are known. We used 3-methoxycarbonyl-4-oxo-4H-1-benzopyran 4 as the substrate.

Zinc-induced reduction of Ethyl 2-Cyano-3-(4-Oxo-4H-1-Benzopyran-3-Yl)Propenoates – a Medium-Dependent Reaction

“…recently. 9 In continuation of our studies on the reductive selfcoupling of 3-functionalised 4-oxo-4H-1-benzopyrans 2 10 and 3, 11 we report herein two chemoselective reductions of alkylidene cyanoacetate 1with Zn under different conditions. Sodium naphthalenide-induced reduction of 1a-c produces complex mixtures, from which the cyclopentadienones 4 were isolated in 5% yield.…”

Synthesis of Chamaecypanone C Analogues from in Situ-Generated Cyclopentadienones and Their Biological Evaluation

“…Mono- or disubstituted cyclopentadienones are less commonly reported, likely due to their instability or tendency towards dimerization. 8c In particular, there are very few examples of 2,4-disubstituted cyclopentadienones reported in the literature, 15 and no reports of 2,4-diarylcyclopentadienones or derived dimers to date.…”

1,2,3‐Triazolophanes—Cyclophanes with an Array of Molecular Structures and Supramolecular Architectures

“…They are well known to bind halide ions, in particular chloride ion, through C-H···halide bonds. [34][35][36][37][38][39] An example of stepwise synthesis of [3 4 ]triazolophane 94 from diazide 91 and alkyne 90 is shown in Scheme 26.…”

“…Both the self association of 94 as well as its ability to form complexes with halide ions have been investigated by NMR and UV-vis spectroscopic methods. [33][34][35][36][37][38][39] Incorporation of pyridine rings in these macrocycles improved the self-association to form the dimers in which the triazolophane rings are p-stacked. For example, the self-association constant for 94 e is 255 m À1 whereas that for 94 d is 12 m À1 in acetonitrile.…”

“…Monomeric 12-to 17-membered macrocyclic triazolophanes incorporating a furanoside ring have been reported. Functional group modification of the isopropylidene protected azidofuronoside (36) shown in a box in Scheme 12 gave a variety of tethers bearing the alkyne functionality (39,41,43 and 45) which on click cycloaddition gave macrocycles of various ring sizes (40, 42, 44 and 46). [18] Glycotriazolophane with para-phenylene spacer has been reported (Scheme 13).…”