Acid catalysed reaction of indanones, tetralones and benzosuberone with neopentyl glycol and other alkanediols under forced conditions (original) (raw)
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The Journal of Organic Chemistry, 2009
When treated with Ac 2 O at rt in the presence of 4-6 mol % FeCl 3 , 2-alkylcinnamaldehydes are converted to 2-alkyl-1H-inden-1-yl acetates through the intermediacy of gemdiacetates. Methanolysis of the indenyl acetates yields the corresponding indenols. Saponification yields 2-alkylindanones, providing, in effect, an intramolecular acylation employing catalytic levels of acid. Geminal dicarboxylates, or acylals, are prepared by the acid-catalyzed reaction between aldehydes and noncyclic anhydrides of carboxylic acids. The reaction is easily accomplished under mild conditions using a variety of Brønsted or Lewis acid catalysts. 1,2 A convenient, solventless procedure is to treat aldehydes with excess acetic anhydride and catalytic quantities of FeCl 3 at 0°C. 3 Acylals have been proposed as aldehyde protecting groups. 2,4 Other synthetic uses are concerned mainly with substitution reactions of a carboxylate group with carbon nucleophiles. 1,5 Acetic acid elimination from the diacetate acylals of R,β-unsaturated aldehydes produces 1-acetoxy-1,3-dienes, which have been used in Diels-Alder reactions. 6 Acylals of R,β-unsaturated aldehydes also have been employed as substrates in Pd-catalyzed allylic substitutions. 7 In the presence of Lewis acids, the acylals of acrolein and 2-alkylacroleins will alkylate aromatic rings, yielding the enol acetates of 3-arylpropanals, the Scriabine reaction. 8 This reaction, which provides a route to 3-arylpropanals, was described by Igor Scriabine in 1961. The transformation was effected by treating the unsaturated acylals with an excess of arene and 1 equiv of TiCl 4 in combination with BF 3 3 Et 2 O. More recent procedures developed for industrial purposes accomplish the reaction using substoichiometric levels of Lewis acid. 8e,8f Recently, we reported that in situ generated dimethyl acetals of (E)-2-alkylcinnamaldehydes cyclize in the presence of catalytic quantities of FeCl 3 , yielding 1-alkoxy-2-alkyl-1H-indenes (1). 9,10 Typically, indene formation was effected using 5-10 mol % FeCl 3 in refluxing MeOAc. These indenes were then transformed in two steps (base-catalyzed doublebond migration to form the enol ether and acid-catalyzed hydrolysis) into 2-alkylindanones (2). Formally, the transformation corresponds to an intramolecular Friedel-Crafts acylation achieved with catalytic quantities of Lewis acid. 11 Traditional Friedel-Crafts acylations require stoichiometric amounts of Lewis acid to proceed to completion because of coordination of Lewis acid with the resulting aryl ketones. On the basis of the precedents of our acetal cyclization and the Scriabine reaction, it seemed plausible that
Metal-free synthesis of indanes by iodine(III)-mediated ring contraction of 1, 2-dihydronaphthalenes
Journal of the Brazilian Chemical Society, 2011
Um protocolo livre de metais foi desenvolvido para sintetizar indanos através da contração de anel de 1,2-di-hidronaftalenos promovida por PhI(OH)OTs (HTIB ou reagente de Koser). Este rearranjo oxidativo pode ser realizado em diversos solventes (MeOH, CH 3 CN, 2,2,2-trifluoroetanol (TFE), 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), e uma mistura 1:4 de TFE:CH 2 Cl 2 ) em condições brandas. A contração de anel fornece indanos trans-1,3-dissubstituídos diastereosseletivamente, os quais são difíceis de obter em química orgânica sintética.
Synthetic studies in dihydroindole and indole alkaloids
1973
A synthetic approach toward the synthesis of vindoline (3) and a reinvestigation of the total synthesis of vincaminoridine (4) and epivincaminoridine (4a) is described. The synthetic sequence involves alkylation with benzyl chloride of the monosodium salt of propane-l,3-diol to give y-benzyloxypropanol (197). Treatment of 197 with thionyl chloride afforded benzyl-ychloropropyl ether (198). Alkylation of ethyl diethyl malonate with 198 provided diethyl Y~D enz yl ox yP ro Pyl etn yl malonate (134). Basic hydrolysis of 134 gave y-benzyloxypropylethyl malonic acid (199), which upon decarboxylation provided 2-(y-benzyloxypropyl)-butanoic acid (200). The monoacid (200) was esterified with ethanol to provide ethyl tx-(y-benzyloxypropyl)-butanoate (135). Alkylation of 135 with allyl bromide gave ethyl-a-(y-benzyloxypropyl)-a-allylbutanoate (201), which upon treatment with osmium tetroxide and sodium periodate gave ethyl a(y-benzyloxypropyl)-a-(a-formylmethyl)butanoate (140). Condensation of 140 with 6-methoxy tryptamine afforded the tetracyclic lactam (150). Lithium aluminum hydride reduction of the latter, followed by hydrogenolysis of the benzyl group gave two isomeric tetracyclic alcohols (204). These intermediates were converted via their mesylate derivatives to the quaternary salts (205), which upon treatment with potassium cyanide gave the isomeric cyanides (216). Acid hydrolysis of 216 gave the corresponding carbomethoxy derivative (151). Alkylation of 151 i i iwith methyl iodide provided dl-vincaminoridine (4) and dlepivincaminoridine (4a). Transannular cyclization of the latter substances gave the pentacyclic aspidosperma-type system (195). The degradation sequence involved acid hydrolysis of vindoline (3) to provide desacetyl vindoline (224), which upon catalytic hydrogenation gave desacetyldihydrovindoline (225). Pyrolysis of 225 afforded the ketone (86), which upon treatment with dimethyl carbonate provided the g-ketoester (226). Treatment of the sodium enolate of 226 with oxygen-hydrogen peroxide gave the hydroxy ketoester (227). Treatment of desacetyldihydrovindoline (225) with N,Nthiocarbonyldiimidazole gave the thiocarbonate derivative (230), which upon desulfurization with Raney nickel afforded the unsaturated ester (231). Catalytic hydrogenation of 231 gave the saturated ester (232) , which upon treatment with lithium diisopropyl amide and oxygen-hydrogen peroxide provided the hydroxyester (234). The saturated ester 232 was converted to the alcohol derivative (237) by reduction with aluminum hydride. Oppenauer oxidation of 237 gave the aldehyde (238). Finally potassium permanganate oxidation of the unsaturated ester (231) gave 5-membered lactam (240), 6-membered lactam (241), N-formyl-5-membered lactam (242), ct and N Q-formyl-6-membered lactam (243) .
Novel Synthesis of 1H-Inden-1-Ones and Thienylpropenones in Aqueous Medium
Journal of the Chinese Chemical Society, 2006
Condensation of acetylacetone with 4-methoxybenzaldehyde, 2,4-dimethoxybenzaldehyde, 3,4-dimethoxybenzaldehyde, 4-nitrobenzaldehyde and 2,4-dinitrobenzaldehyde in water and in the presence of cetyltrimethylammonium bromide (CTABr) as cationic surfactant in dilute sodium hydroxide at room temperature did not afford the expected arylideneacetylacetone but yielded 1H-inden-1-one derivatives 1, while, with piperonaldehyde under the same conditions afforded dipiperonylideneacetone 2. Also 3-acetylthiophene condensed with some aromatic aldehydes under the same conditions gave the expected stereoselective thienylpropenones 4. The structures of the products were identified by IR, NMR, Mass spectral data and elemental analysis.
This is the sixth chapter in the series published by the same authors: “The Organic Chemistry Notebook Series, a Didactical Approach”. Here we offer the mechanistic views of the synthesis of alkenes by oxidative decarboxylation of carboxylic acids. The aim of this series of studies is to help students to have a graphical view of organic synthesis reactions of diverse nature. The oxidative decarboxylation of carboxylic acids is a useful method for generating alkenes. Here we propose the mechanism and its discussion for the application of the method of decarboxylation of diacids lacking nearby double bonds. Also, the route is explained mechanistically for the preparation of Dewar benzene. The thermal or photolytic decomposition of di-t-butyl per-esters is described. The treatment of monocarboxylic acids to afford alkenes in the presence of lead tetraacetate and copperII acetate is briefly discussed. The alkylation-decarboxylation of aromatic acids is also explained. The oxidative decarboxylation of carboxylic acids can eventually conduct to the obtaining of ketones instead of alkenes. We have used a series of reactions reviewed by W. Carruthers, and we have proposed didactical and mechanistic views for them. This latest approach is included in the synthetic methods reviewed by W. Carruthers with respect to the “Formation of carbon-carbon double bonds”. Spanish title: Síntesis de alquenos por descarboxilación de ácidos carboxílicos; vistas mecanísticas; De la serie: El cuaderno de notas de química orgánica, un enfoque didáctico, Nº6.