Cyclische Verbindungen mit Heterobrückenatomen, IX. 3a‐Azaazulen‐4‐one

Flitsch, Wilhelm; Müter, Bernhard; Wolf, U.

doi:10.1002/cber.19731060627

Cited by 26 publications

(4 citation statements)

References 11 publications

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“…Finally, a quite spectacular rearrangement sequence is observed for (Z/E)-2 g (X OPh) in the presence of HBF 4 : Ring closure (2 g 34 g, X OPh) followed by ring opening (4 g 36 g) and final addition/elimination (6 g 38 PhOH) gives the well-known [17] 3a-aza-azulen-4-one 8.…”

Section: Methodsmentioning

confidence: 91%

Rearrangement of 5-Substituted 5-Aminopentadienals

Fischer

Berger

Neuenschwander

1998

Angewandte Chemie International Edition

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Section: Methodsmentioning

confidence: 91%

Rearrangement of 5-Substituted 5-Aminopentadienals

Fischer

Berger

Neuenschwander

1998

Angewandte Chemie International Edition

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“…13%) was present in the soluble fraction and was identified by its characteristic resonance at δ H 8.20 (1H, m). 27 The pyrolysate from FVP of 46 (0.027 g, 700 ЊC, 100 ЊC, 0.001 Torr, 20 min) was examined by 1 H NMR spectroscopy. No trace of the azaazulenone 48 was obtained and the only identifiable product was pyrrole (see Discussion section).…”

Section: Pyrolysis Of Compounds 45 and 46mentioning

confidence: 99%

Synthesis of pyrrolizin-3-ones by flash vacuum pyrolysis of pyrrol-2-ylmethylidene Meldrum’s acid derivatives and 3-(pyrrol-2-yl)propenoic esters

Campbell¹,

Comer²,

Derbyshire³

et al. 1997

J. Chem. Soc., Perkin Trans. 1

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Monosubstituted pyrrolizin-3-ones 1 with substituents at the 1-, 5-, 6-or 7-positions are prepared in excellent yield by flash vacuum pyrolysis (FVP) of appropriate Meldrum's acid derivatives 2. The mechanism involves formation of the pyrrol-2-ylmethylideneketene 29, which can also be generated thermally from 3-(pyrrol-2-yl)propenoate esters (e.g. 30). This alternative route has been used to make a range of 2-substituted pyrrolizin-3-ones, again in excellent yield. The 3-oxo-3H-pyrrolizine-2-carboxylic acid 42 could not be made in this way owing to facile decarboxylation to pyrrolizinone 1, and extension to the formation of the azaazulenone 48 was again unsuccessful.Some years ago we reported a simple and efficient synthesis of pyrrolizin-3-one 1 by flash vacuum pyrolysis (FVP) of the condensation product 2 of pyrrole-2-carbaldehyde and Meldrum's acid. 1 Later, we applied this methodology to the crystalline 6-bromo derivative 3, 2 and obtained the first X-ray crystallographic data for this ring system. 2 The Meldrum's acid route was also used to make certain azapyrrolizinone ring systems for the first time, 3 and their NMR spectra have been discussed in detail. 4 Since pyrrolizinones remain relatively unexplored in the literature, 5 we now report a more extensive study of the scope and mechanism of this synthetic route from which a complementary pyrolytic synthesis via pyrrolylpropenoic esters has evolved. 6 Our corresponding work on the azapyrrolizinones is discussed in the accompanying paper. 7Two routes to the key Meldrum's acid precursors were employed (Scheme 1). The classic Knoevenagel condensation N R 6 O O O O O N H 3 R 6 = Br 1 R 6 = H 2 Scheme 1 Reagents and conditions: i, piperidinium acetate, toluene, 20 ЊC; ii, acetonitrile, 20 ЊC O O O O N H R O O O O O O O O OMe N H R N H CHO ii i Route b Route a + + 4 Rusing piperidinium acetate catalyst 8 in toluene at room temperature (Scheme 1, route a) works well if the appropriate pyrrole-2-carbaldehyde is readily available. Thus, we have used the photochemical ring contraction of 4-substituted pyridine N-oxides 9-11 to prepare a range of 3-substituted pyrrole-2-carbaldehydes 5-7 containing electron donating and electron withdrawing groups, and we prepared ethyl 5-formylpyrrole-2-carboxylate 8 by Vilsmeier formylation of the ester using a literature method. 12 Yields for the Meldrum's acid condensation to give the derivatives 10-13 were in the range 62-98%. Condensation of Meldrum's acid with 2-acetylpyrrole 9 was achieved by the titanium tetrachloride method 13 though the yield of 18 obtained in this way was consistently lower than for the aldehyde reactions (57%). We have also reported a direct route to 2 by reaction of N H CHO R 3 N H CHO EtO 2 C N H Me O O O O O O O O O N H Me 9 8 5 R 3 = Me 6 R 3 = OMe 7 R 3 = CO 2 Me N R 4 R 3 R 5 H 18 10 R 3 = Me, R 4 = R 5 = H 11 R 3 = OMe, R 4 = R 5 = H 12 R 3 = CO 2 Me, R 4 = R 5 = H 13 R 3 = R 4 = H, R 5 = CO 2 Et 14 R 3 = R 4 = H, R 5 = Me 15 R 3 = R 4 = H, R 5 = Ph 16 R 3 = Ph, R 4 = R 5 = H 17 R 3 = R 5 = H, R 4...

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“…Dabei wird in einer Kette von Umlagerungen (Ringschluû zum 2-Pyrrolopyryliumsalz 4 g (X OPh), Ringöffnung zum 5-Phenoxypentadiensäurepyrrolamid 6 g und Ringschluû zum Bicyclus 8) das bekannte [17] 3a-Azaazulen-4-on 8 gebildet.…”

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Umlagerung von 5-substituierten 5-Aminopentadienalen

1998

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Nur mit starken Nucleophilen erfolgt die Ringöffnung 3→4, da die aus 5‐X‐substituierten 5‐Aminopenta‐2,4‐dienalen 2 säurekatalysiert gebildeten 2‐Aminopyryliumsalz‐Zwischenstufen 3 wegen der „aromatischen”︁ Stabilisierung recht reaktionsträge sind. Dies ermöglicht demgegenüber allerdings die direkte Synthese zahlreicher 2‐Aminopyryliumsalze 3 aus „Push‐pull”︁‐Eninen 1. X=OAc, F, Cl, Br, I, OPh.

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Cyclische Verbindungen mit Heterobrückenatomen, IX. 3a‐Azaazulen‐4‐one

Cited by 26 publications

References 11 publications

Rearrangement of 5-Substituted 5-Aminopentadienals

Rearrangement of 5-Substituted 5-Aminopentadienals

Synthesis of pyrrolizin-3-ones by flash vacuum pyrolysis of pyrrol-2-ylmethylidene Meldrum’s acid derivatives and 3-(pyrrol-2-yl)propenoic esters

Umlagerung von 5-substituierten 5-Aminopentadienalen

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