Eine Partialsynthese des „all”︁‐trans‐Methyl‐bixins und des „all”︁‐trans‐4.4′‐Desdimethyl‐methyl‐bixins

Buchta, Emil; Andree, Franz

doi:10.1002/cber.19590921214

Cited by 57 publications

(6 citation statements)

References 20 publications

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“…Oxidation of the primary alcohol was best achieved with Dess–Martin periodinane; Swern oxidation resulted in partial epimerization at C6. Wittig reaction using phosphonium salt 7 a 16 gave moderate yields only (46 %), and the phosphine oxide was difficult to remove by chromatography. In contrast, the Horner–Wadsworth–Emmons olefination with phosphonate 7 b and LDA17 delivered 2 E ,4 E dienoate 15 as a single stereoisomer in excellent yield (up to 96 %, 4 E :4 Z >50:1).…”

Section: Methodsmentioning

confidence: 99%

Total Synthesis of Efomycine M

Barth

Mulzer

2007

Angew Chem Int Ed

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Section: Methodsmentioning

confidence: 99%

Total Synthesis of Efomycine M

Barth

Mulzer

2007

Angew Chem Int Ed

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“…The Meldrum's acid derivative 45 was prepared by Knoevenagel condensation of the aldehyde 47, whereas the pentadienoate 46 was obtained from pyrrole-2-carbaldehyde and the appropriate Wittig reagent. 26 However, pyrolysis of 45 at 600 ЊC gave a material whose 1 H NMR spectrum was complex with only small peaks attributable to the expected azaazulenone 48 27 (ca. 13%), partly owing to the poor volatility of the precursor.…”

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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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“…Hydrolysis of the 5,6-0-isopropylidene group of VI was performed by the treatment of VI with 70 % aqueous acetic acid to give a crystalline diol VII, mp 128.5°C, almost quantitatively. Periodate oxidation of VII, followed by the treatment of aldehyde with [3-carbomethoxypropen-(2)-yliden-(1) ]tripheny lphosphorane"& 7 ). gave an unsaturated ester VIII in 67 % yield.Catalytic hydrogenation of vm over 10% Pd-C in ethanol gave a saturated hemiacetal IX in 76 % yield.…”

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confidence: 99%