Unprecedented Vilsmeier formylation: expedient syntheses of the cruciferous phytoalexins sinalexin and brassilexin and discovery of a new heteroaromatic ring system

[reaction: see text]. A very concise first synthesis of sinalexin was achieved by regioselective formylation of 1-methoxyindoline-2-thione under Vilsmeier conditions followed by unprecedented ammonia workup. Similar formylation of indoline-2-thione yielded brassilexin and a novel pentacyclic heteroaromatic compound resulting from condensation of the Vilsmeier adduct of indoline-2-thione. Both sinalexin and brassilexin displayed strong antifungal activity against several pathogens of crucifers.     

Reduction of Indolin-2-ones and Desulfurization of Indoline-2-thiones to Indoline and Indole Derivatives

Reduction of indolin-2-ones with lithium aluminium hydride (LAH) or diisobutylaluminum hydride (DIBAL) and desulfurization of indoline-2-thiones with Raney-Ni were investigated. Treatment of indoline-2-ones 1 with LAH or DIBAL yield indoles 4 and/or indolines 3 in moderate-to high yield depending on the substituents at N and C(3) of 1 . Indoline-2-thiones 2 were desulfurized with Raney-Ni to give indoles 4 and/or indolines 3 .     

Synthesis of Indole Derivatives by [2 + 2] Photocycloaddition of Indoline-2-thiones with alkenes and photodesulfurization of indoline-2-thiones

The photochemical synthesis of indole derivatives starting from the indoline-2-thiones 1 is described. Irradiation of indoline-2-thiones 1 in the presence of alkenes 3 gave 2-alkyl-3H-indoles 4 – 7 or 2-alkylindoles 8 – 22 through the ring cleavage of the intermediates, spirocyclic amino-thietanes, initially derived by [2 + 2] cycloaddition of the C?S bond of 1 and the C?C bond of 3 . Irradiation of 1 in the presence of trialkylamines 26 gave desulfurization products 27 – 32 and unexpected 3-alkylindoles 33 – 40 . N-Acylindoline-2-thiones 11 - p yielded the deacylated products, indoline-2-thiones 1a - b , and ethyl esters 43 through γ-H abstraction by the excited thioamide S-atom when irradiated in CDC1₃/EtOH or benzene/EtOH. Oxygen analogues 2a - d also underwent intramolecular H abstraction to give the indolin-2-ones 2e – f and ethyl esters 43 in a similar way.     

Detoxification pathways of the phytoalexins brassilexin and sinalexin in Leptosphaeria maculans: isolation and synthesis of the elusive intermediate 3-formylindolyl-2-sulfonic acid

Brassilexin and sinalexin are among the most potent antifungal phytoalexins produced by crucifer plants. Nonetheless, the crucifer pathogen Leptosphaeria maculans(Desm.) Ces. et de Not. (asexual stage Phoma lingam(Tode ex Fr.) Desm.) is able to detoxify these phytoalexins. To understand and control these reactions, the elusive brassilexin and sinalexin detoxification pathways in L. maculans were investigated and compared to those of the synthetic derivatives 8-methylbrassilexin and 8-acetylbrassilexin. The chemical structures, syntheses and antifungal activities of the metabolic intermediates, including the most polar metabolite identified thus far, 3-formylindolyl-2-sulfonic acid, were established. Our overall findings suggest that the first detoxification step of brassilexin involves its reductive bioconversion to 3-aminomethyleneindole-2-thione, followed by hydrolysis and oxidation to the water soluble metabolite 3-formylindolyl-2-sulfonic acid.     

Phytoalexins from the crucifer rutabaga: structures, syntheses, biosyntheses, and antifungal activity

Phytoalexins are inducible chemical defenses produced de novo by plants in response to diverse forms of stress, including microbial attack. Our search for phytoalexins from economically important crucifers lead us to examine rutabaga tubers (Brassica napus L. ssp. rapifera). Three new phytoalexins, named isalexin (9), brassicanate A (10), and rutalexin (11), were isolated together with five known phytoalexins, brassinin (4), 1-methoxybrassinin (5), spirobrassinin (13), brassicanal A (14), and brassilexin (15). The chemical structures of the new phytoalexins were proven by syntheses, and their biological activity against four plant pathogens were determined. Biosynthetic studies using tetra- and pentadeuterated precursors established that indolyl-3-acetaldoxime (22) and brassinin (4) are precursors of brassicanate A (10) and rutalexin (11) and that cyclobrassinin (23) is a biosynthetic precursor of rutalexin (11), whereas tryptamine (24) is not a precursor of rutabaga phytoalexins.     

BF3 etherate-mediated microwave-assisted facile synthesis of thiopyrano[2,3-b]indol-2-one

A facile synthesis of indole annulated 2H-thiopyran-2-ones has been developed by condensation of indoline-2-thiones with acetoacetic esters in the presence of borontrifluoride etherate (BF₃ etherate) using microwave irradiation. This one-step operationally simple methodology leads to thiopyrano[2,3-b]indol-2-ones in good yields.     

One-pot syntheses of 2-pyrazoline derivatives

Hydrazinediium dithiocyanate and α,β-unsaturated ketones give in one-pot reactions 1-thiocarbamoyl-2-pyrazolines and 1-formyl-2-pyrazolines. The syntheses of pyridine-2-thiones, pyrimidine-2-thiones and bicyclo[2.2.2]octan-2-ones from ammonium thiocyanates and ketones by analogous procedures are reviewed. The mechanisms of the ring formations are discussed. Crystal structure analyses of a 1-thiocarbamoyl- and a 1-formyl-2-pyrazoline are given.     

Gold(I)-catalyzed sequential cycloisomerization/bis-addition of o-ethynylanilines: an efficient access to bis(indolyl)methanes and di(indolyl)indolin-2-ones

An efficient synthesis of bis(indolyl)methanes and di(indolyl)indolin-2-ones has been developed by a sequential approach involving gold(I)-catalyzed cycloisomerization/bis-addition of o-ethynylanilines with various aldehydes and isatins, respectively. This methodology opens clean and synthetically competitive alternative to the already established procedures of the synthesis of bis(indolyl)methanes and di(indolyl)indolin-2-ones.     

A divergent synthesis of functionalized unsaturated delta-lactones from alpha-alkenoyl-alpha-carboxyl ketene dithioacetals

A divergent synthesis of functionalized unsaturated delta-lactones 2, 3, 4, and 5 has been developed starting from the readily available alpha-alkenoyl-alpha-carboxyl ketene dithioacetals 1 in high to excellent yields under mild reaction conditions. Thus, 6-substituted 3-(1,3-dithiolan/dithian-2-ylidene)-3H-pyran-2(6H)-ones 2, obtained from a consecutive reduction with NaBH4 and acidic workup of 1 via a novel vinylogous Pummerer cyclization, can be further transformed into alpha-pyranones 3, 4, and 5 upon a sequential isomerization catalyzed by triethylamine (to give 3), followed by dethioacetalization (to give 4) or a formylation with Vilsmeier reagent (to give 5).     

Rapid and Efficient Synthesis of 3,3-Di(1H-indol-3-yl)indolin-2-ones and 2,2-Di(1H-indol-3-yl)-2H-acenaphthen-1-ones Catalyzed by p-TSA

An efficient synthesis of 3,3-di(1H-indol-3-yl)indolin-2-ones and 2,2-di(1H-indol-3-yl)-2H-acenaphthen-1-ones via a reaction of various isatins or acenaphthenequinone with indoles in the presence of p-methylbenzene sulfonic acid (p-TSA) in CH₂Cl₂ at room temperature is described. The advantages of this method include good reaction yield, simple workup procedure, and mild reaction condition.     

Unprecedented Multicomponent Reaction of Indoles,CS2 and Nitroarenes: Stereoselective Synthesis of (Z)-3-((Arylamino)methylene)indoline-2-thiones

An efficient method for the stereoselective synthesis of (Z)-3-((arylamino)methylene)indoline-2-thiones have been developed via a novel multicomponent reaction of indoles, CS₂ and nitroarenes. A range of functionalized indoline-2-thiones were prepared in moderate to good yields from easily available starting materials. The indoline-2-thione products can be easily derivatized to give biologically active thieno[2,3-b]indole and thiopyrano[2,3-b]indole skeletons in high yields.     

General synthesis of mono-, di-, and tri-acetylated indoles from indolin-2-ones

Having developed the one-pot triacetylation of indolin-3-ones, we have now devised a simple two-step reaction sequences to produce di- and mono-acetylated indoles from indolin-2-ones. The indolin-2-ones were first subjected to acetylation in the presence of acetic anhydride and a catalytic amount of N,N-dimethylaminopyridine to give 2-acetoxy-1,3-diacetylindoles. Subsequently, an enzyme-assisted deacetylation resulted in the chemoselective deprotection of the acetoxy group to produce 1,3-diacetyl-2-hydroxyindoles. However, a chemical deacetylation of 2-acetoxy-1,3-diacetylinoles under mild basic or acidic conditions resulted in the formation of 3-acetyl-2-hydroxyindoles.     

Synthesis of derivatives of the new condensed system 4H,7H-furo[3′,4′:6,7]cyclohepta[1,2-<Emphasis Type="Italic">b</Emphasis>]pyran

8-Hydroxy-1,3-dimethyl-4H-cyclohepta[c]furan-4-one reacts with arylidenemalononitriles and, like 1,3-oxo enols, forms the corresponding condensed 2-amino-4H-pyrans. The analogous reaction with 3-(dicyanomethylene)indolin-2-ones give spirocyclic 2-amino-4H-pyrans. The 4-aminopyrimidine ring is formed on the basis of the enamino nitrile fragment of the new pyrans by successive reaction with triethoxymethane and then with aqueous ammonia. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 188–195, February, 2008.     

4-Hydroxy-2-quinolones. 107. Reaction of triethyl methanetricarboxylate with indoline

The first stage of the reaction of triethyl methanetricarboxylate with indoline is the formation of the diethyl ester of 2-(indoline-1-carbonyl)malonic acid, which then, depending on the conditions selected, may be converted into the ethyl ester of 2-(indoline-1-carbonyl)-3-(indolin-1-yl)-3-oxopropionic acid, methanetri-N-(indolin-1-yl)carboxamide, or the ethyl ester or (indolin-1-yl)amide of 1-hydroxy-3-oxo-5,6-dihydro-3H-pyrrolo[3,2,1-ij]quinoline-2-carboxylic acid. __________ Translated From Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1191–1197, August, 2006.     

Copper-catalyzed synthesis of 2-sulfenylindoles from indoline-2-thiones and aryl iodides

A novel and efficient method for synthesis of 2-sulfenylindole via copper-catalyzed coupling reaction of indoline-2-thiones with aryl iodides has been developed. A series of N-substituted and N-free 2-sulfenylindole were obtained in high yields. Furthermore, the method was employed to synthesis of benzothieno[2,3-b]indoles from indoline-2-thiones with 1,2-diiodobenzene in the presence of CuI and Pd(OAc)₂ as catalysts.     

Triflic anhydride-mediated tandem formylation/cyclization of cyanoacetanilides: a concise synthesis of glycocitlone alkaloids

A method is presented for the concise synthesis of 3-formyl-4-hydroxyquinolin-2(1H)-ones through triflic anhydride-mediated tandem formylation/cyclization of cyanoacetanilides. This tandem process was successfully used for the rapid syntheses of glycocitlones A and C.     

Preparation and alkylation of regioisomeric tetrahydrophthalimide-substituted indolin-2(3H)-ones

A series of novel regioisomeric tetrahydrophthalimide-substituted indolin-2-ones has been prepared via the Sommelet-Hauser type cyclization of appropriately substituted anilines as potential herbicides. The resultant indolin-2-ones were then regioselectively alkylated at N-1 and C-3 to give 1,3,3-trisubstituted indolin-2-ones. The most active series was also prepared by the bis-nitration of m-fluorophenylacetic acid followed by reduction and cyclization to give 6-amino-5-fluoroindolin-2-one. Elaboration to the tetrahydrophthalimide-substituted indolin-2-one was followed by C- and N-alkylation to give the desired compounds.     

A facile and efficient synthesis of polyfunctionalized pyridin-2(1H)-ones from beta-oxo amides under Vilsmeier conditions

A facile and efficient one-pot synthesis of polysubstituted pyridin-2(1H)-ones from a variety of beta-oxo amides under Vilsmeier conditions is described, and a mechanism involving sequential halogenation, formylation and intramolecular nucleophilic cyclization is proposed.     

Construction of C2-Spirocyclopropyl-Indolin-3-Ones through Base-Promoted [2+1] Annulation Reaction of Indolin-3-ones with Bromosulfonium Salts

A simple base-promoted [2+1] annulation of indolin-3-ones and bromosulfonium salts has been developed in this article. This strategy uses simple and easily prepared indolin-3-ones 1 as C1 synthons and bromosulfonium salts 2 as C2 synthons under mild reaction conditions, and 33 examples of C2-spirocyclopropyl-indolin-3-ones were obtained with up to 99 % yield and >20 : 1 dr.     

Syntheses with ketones,sulfur, and ammonia or amines at room temperature

A large number of preparatively interesting compounds have become readily available by the simultaneous action of sulfur and ammonia or amines on ketones. Direct syntheses of Δ³-thiazolines, Δ³-imidazoline-5-thiones, 5,6-dihydro-4H-1,4-thiazines, and the 1,2,3,4,5,6-hexathiocane system from ketones, sulfur, and ammonia or amines, and further possibilities for the synthesis of these heterocyclic systems have been proposed. Other heterocycles containing N or N and S (thiazoles, thiophenes, thiazolidines, tetrahydrothiazolo[2,3-c]-1,4-thiazines, thiomorpholines, 4-amino-2H-imidazoles, etc.) are readily obtainable by further reactions of these compounds. Hydrolysis of the Δ³-thiazolines yields α-mercapto ketones, which are the starting materials for other syntheses. Most of the syntheses described proceed at room temperature and at normal pressure.