Variations of the Fischer and Piloty syntheses

Posvic, Harvey; Dombro, Robert; Ito, Hiroyasu; Telinski, Thomas

doi:10.1021/jo00931a027

Cited by 47 publications

(7 citation statements)

References 6 publications

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“…The para Claisen rearrangement of 250 to 251 represented a case where acid catalysis led to a fair yield of product that was inaccessible by the uncatalyzed route. (Thermal rearrangement of 250 gave a mixture containing cleavage product and iV-(7,7-dimethylallyl)-2,6-dimethylaniline.)…”

Section: H Enzyme Catalysismentioning

confidence: 99%

Catalysis of the Cope and Claisen rearrangements

Lutz¹

1984

Chem. Rev.

498

171

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Section: H Enzyme Catalysismentioning

confidence: 99%

Catalysis of the Cope and Claisen rearrangements

Lutz¹

1984

Chem. Rev.

498

171

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“…Thus methods for preparing pyrroles containing both symmetrically [8] and unsymmetrically placed substituents have been proposed [9,10]. In addition, variants of the Piloty-Robinson synthesis have been reported using microwave irradiation [11], solid-phase synthesis [12] or base catalysis [13] conditions.…”

mentioning

confidence: 99%

The Piloty-Robinson reaction of N-substituted piperidin-4-one azines. A novel route for the synthesis of 3,6-diazacarbazole

Alekseyev

Kurkin

Yurovskaya

2011

Chem Heterocycl Comp

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In 1960 O. Piloty discovered that diethyl ketone azine with an excess of anhydrous zinc chloride was converted to 2,5-diethyl-3,4-dimethylpyrrole at 230ºC in 25% yield [1]. G. and R. Robinson reported in 1918 that heating desoxybenzoin azine at 180ºC in a stream of hydrogen chloride gave 2,3,4,5-tetraphenylpyrrole in 88% yield [2]. This method of preparing pyrroles by heating the corresponding carbonyl compound azines in the presence of an acidic reagent has since been called the Piloty-Robinson reaction [3]. In a series of studies [1, 2, 4, 5] there were undertaken unsuccessful attempts to extend this synthetic route to azines of other carbonyl compounds, viz: butyric and isovaleric aldehydes, acetone, cyclopentanone, butyrone, and acetophenone. However, cyclohexanone azine (1) could be successfully cyclized to 2,3,4,5,6,7,8,9-octahydro-1H-carbazole (2) by refluxing in tetralin in an HCl atmosphere in 28% yield [6]. A. N. Kost and I. I. Grandberg reported [5] that compound 2 could be prepared in 79% yield by heating the azine 1 with anhydrous zinc chloride and also that the N-acetyloctahydrocarbazole could be prepared in 82% yield by refluxing in dioxane with acetyl chloride.It was thought that the mechanism of the Piloty-Robinson reaction is similar to that of the Fischer synthesis of indoles. Acid causes a tautomeric conversion of the azine to the bisenehydrazine which undergoes a [3,3] sigmatropic rearrangement accompanied by formation of a novel C-C bond and cleavage of the N-N bond with closure to a pyrrole ring via loss of a molecule of ammonia [2, 7].

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“…The free base was isolated after a mixture of 0.150 g (0.005 mol) of 8b HC1 and 4 ml (0.08 mol) of 2 N NaOH was heated to reflux for 2 days in 15 ml of methanol: yield 75 mg (57%); mp 116-118 °C; m/e 242 (M+); NMR (CDC13 + Me2SO) 1.23 (d, 3, J = 6 Hz, CH3), 3.0 (s, 1, exchangeable with D20, NH), 10),3,C6H3),1,CeHO. l,2,3,4,5,6,7,pyrimido-[l,2-a]indole (9). To the suspension of 0.2 g (0.005 mol) of lithium aluminum hydride in 25 ml of anhydrous ether there was added 0.050 g (0.0002 mol) of 8b.…”

Section: Methodsmentioning

confidence: 99%

“…To demonstrate the generality of the reduction with diborane, both compounds 5e and 5f were subjected to this reagent. Reduction of the free base of 5e and the subsequent treatment with hydrogen chloride lead to the known4 5-(3aminopropyl)-6,7,8,9,10,ll-hexahydro-5if-cyclooct [6]indole hydrochloride (7b). Reduction of the free base of 5f (mp 84-85 °C) gave 5-(3-aminobutyl)-6,7,8,9,10,ll-hexahydro-5/i-cyclooct[i>] indole (7c), which was isolated as the hydrochloride in 65% yield.…”

Section: Scheme Imentioning

confidence: 99%