Pyridinium ylides in syntheses of naphthopyrandiones and in regioselective syntheses of acylated anthraquinones related to fungal and bacterial metabolites

Abstract

Improvements have been made in the use of acylated pyridinium ylides for the transformation of 2methyl-l,4-naphthoquinone into derivatives (1 5) and (1 6) of naphtho[2,3-c] pyran-5,l O-dione, containing furan and thiophene groups. The substitution and cyclisation steps can be combined effectively by using 2-phenoxymethyl-instead of 2-methyl-naphthoquinone. The use of better leaving groups than phenoxy (especially 4-nitrophenoxy) allows the quinone to react with two proportions of ylide and leads regiospecifically to 1 -aroyl-2-arylanthracene-9,1 O-diones such as (20a). If the leaving group is nuclear bromine as in 2-bromo-3-methyl-l,4-naphthoquinone, another reaction with 2 mot equiv. of ylide leads to complex red intermediates of type (31) which in contact with alumina are quantitatively converted into the regioisomeric 2-aroyl-3-arylanthracene- 9,l O-diones such as (22a).The structures have been determined by standard methods but special features of the NMR spectra are reported including a case of extreme line broadening by traces of iron. Mechanisms are suggested for the diverse reactions between the quinones and the ylides.A small but significant group of natural products is based upon the naptho[2,3-c]pyran nucleus and contains members with antitumour and/or antibacterial activities2 We have improved and extended the route to such compounds from naphthoquinones and pyridinium y l i d e ~, ~ and found that it can be extended to regiospecific syntheses of acylated anthraquinones similar to antibiotic X-1488 1 C (Streptomyces) and altersolanol B4 and related to some of the highly physiologically active naphthacene quinones.' Results and DiscussionPaper 9/04753K

Microwave-assisted four-component, one-pot condensation reaction: an efficient synthesis of annulated pyridines

“…[15][16][17][18] Pyridinium cations with stronger electron-withdrawing carbonyl, cyano and nitro groups increase the activity of the methylene group and have much more versatile applications. N-Phenacylpyridinium bromide in the presence of a base is known to undergo, for example, Knoevenagel condensation with aldehydes, 19, 20 Michael addition to a, b-unsaturated carbonyl compounds 21, 22 and dipolar cycloaddition with activated alkenes. 23 Therefore, it is worthwhile investigating new types of reactions and synthetic applications of this kind of salt with emphasis on multicomponent reactions College of Chemistry & Chemical Engineering, Yangzhou University, Yangzhou, 225002, China.…”

Stereoselective Cyclopropanation to Homoquinones from Phenacyl Carbenes Obtained through Quinone-Electrogenerated Bases

“…Quinones 1 are Michael acceptors that can incorporate phenacyl groups when attacked by pyridinium ylides. 24 However, under the described ionic pathway using ylides, the plausible homoquinone formation was never observed. This fact let us to discard the possibility to get the cyclopropane by a .…”

Efficient Method for Synthesis of Angucyclinone Antibiotics via Gold-Catalyzed Intramolecular [4 + 2] Benzannulation: Enantioselective Total Synthesis of (+)-Ochromycinone and (+)-Rubiginone B2

“…The bromonaphthoquinone 22 was prepared from 1,5-dihydronaphthalene in four steps in 74% yield by the known procedure . The introduction of the allyl group to the quinone part of 22 was carried out using vinyl acetic acid in the presence of silver nitrate, ammonium persulfate, and 23 was obtained in 65% yield. , Reduction to the hydroquinone of 23 using SnCl 2 and concentrated HCl in EtOH, followed by treatment of the resulting 1,4-dihydroxynaphthalene with Me 2 SO 4 under basic conditions gave 24 in 97% yield. The terminal olefin on the allyl group of 24 was isomerized to the internal one by KO t- Bu in tetrahydrofuran (THF) and 25 was obtained in 92% yield as a 95:5 mixture of trans and cis isomers .…”