Synthese und Eigenschaften von<i>o</i>-hydroxyphenyl- und<i>o</i>-acetylaminophenyl-substituierten Cyclopropenonen. Eine neuartige thermische Umwandlung funktionalisierter Diarylcyclopropenone

A new synthetic method for the preparation of benzofurans has been developed. The key step of this method is the [3,3]‐sigmatropic rearrangement of N‐trifluoroacetyl‐ene‐hydroxylamines, which was triggered by acylation of oxime ethers. TFAA has been proved to be the best reagent to induce [3,3]‐sigmatropic rearrangement for the synthesis of cyclic oracyclic dihydrobenzofurans. On the other hand, the TFAT‐DMAP system is found to be the most effective for constructing various benzofurans. Synthetic utility of this reaction is demonstrated by the short synthesis of natural benzofurans without protection of the hydroxy group. The synthesis of Stemofuran A was accomplished via condensation of ketones with aryloxyamine and subsequent reaction with TFAT‐DMAP in a four‐step synthesis with 72 % overall yield. Similarly, Eupomatenoid 6 and Coumestan were synthesized through the reaction of oxime ether with TFAT‐DMAP. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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“…5‐Methyl‐2‐phenylbenzofuran (14Ce): 43 Colorless crystals. M.p.128–130 °C (EtOH) (ref 43. 125–126 °C).…”

Section: Methodsmentioning

confidence: 99%

Efficient Synthesis of Benzofurans Utilizing [3,3]‐Sigmatropic Rearrangement Triggered by N‐Trifluoroacetylation of Oxime Ethers: Short Synthesis of Natural 2‐Arylbenzofurans

2007

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“…371 The photochemical decarbonylations are generally clean and of high yield, thus providing a synthetically useful method for the preparation of acetylene derivatives. This process was applied for the preparation of diarylcyclopropenones (eq 223; R 1 ) R 2 ) aryl) 9,214,358 and alkoxyarylcyclopropenones (eq 223; R 1 ) aryl, R 2 ) alkoxy). 215 Diarylcyclopropenones have also been converted to acetylenes with high efficiency by heating in 1,2dichlorobenzene in the presence of Al 2 O 3 .…”

Section: G Decarbonylationmentioning

confidence: 99%

“…The synthesis of nonsymmetric cyclopropenone has been done by stepwise arylation with two different aromatic compounds. 15a,, For example, initial addition of 1 equiv of benzene to trichlorocyclopropenylium ion at 0 °C formed a stable intermediatedichloro(phenyl)cyclopropenylium ion, which was further arylated by the addition of a second aromatic molecule to form the desired ketone 250 (eq 140).

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Section: Synthesis Of Cyclopropenones and Heteroanaloguesmentioning

confidence: 99%

“…2-Phenyl-3-(2-hydroxyphenyl)cyclopropenones have been found to undergo thermal rearrangement induced by the intramolecular attack of hydroxyl oxygen to the carbonyl carbon to give lactones 414 and 415 (eq 222) …”

Section: F Rearrangementmentioning

confidence: 99%

“…(eq 221), triphenylphosphine attacks at the vinylic carbon of cyclopropenethiones, to form adduct 410, which attacks another molecule of the cyclopropenethione. The resulting dimeric intermediate 411 is converted to 409 via bis(vinylcarbene) 412, but when R 2 ) SBu t , 408 is formed via bisallene 413.2-Phenyl-3-(2-hydroxyphenyl)cyclopropenones have been found to undergo thermal rearrangement induced by the intramolecular attack of hydroxyl oxygen to the carbonyl carbon to give lactones 414 and 415 (eq 222) 214. …”

mentioning

confidence: 99%

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