Benzofurane skeleton

Fluorescent derivatizing reagents with benzofuran skeleton for HPLC with spec-trometric detection 98YZ483. 

The intramolecular Heck reaction to construct the polycyclic benzofuran skeleton in morphine was reported by Overman [21] in their synthesis of (+)- and (-)-dihydroisocodeine in 1993, and after that, the Heck cyclization has been extensively studied by Cheng [22], Hsin [23, 24], Hudlicky [25] (see Sect. 2.2.3), Trost (see Sect. 2.2.1), and Guillou (see Sect. 2.1.2). In Fukuyama s synthesis, the Heck reaction of 11 works well and successfully provided the A-C-E tricyclic ring system 13 in 87% yield after deprotection of the TBS group in the intermediary enol ether 12. 

In 2002, Trost and Tang reported the chiral total synthesis of (-)-codeine in short reaction steps using a palladium-catalyzed asymmetric allylic alkylation (AAA) [53] as the key transformation [54], In 2005, a detailed full account of their synthesis was published [55]. The key features of their synthesis are (1) a preparation of an aryl ether with high optical purity by the Pd-catalyzed AAA reaction, (2) the intramolecular Heck reaction to generate the A-C-E benzofuran skeleton, (3) the second intramolecular Heck reaction of Z-vinyl bromide providing the phenan-throfuran core, and (4) the intramolecular hydroamination for the construction of D-ring by the action of LDA and visible light. 

We are currently attempting to synthesise [51] the new antilipoperoxidant natural toumefolal and toumefolic acid [52], Fig. (17) using this procedure as a key step in the building of benzofuran skeleton. 

The tricyclic cyclopenta[Z ]benzofuran skeleton of rocaglamide47 (an antileukemia agent extracted from Aglaia elliptifolid) has been successfully produced by sunlamp irradiation of 46 in the presence of diphenyldisulfide (equation 41). This work is connected to the... 

The benzofuran skeleton is common in natural products. A direct synthesis from o-arylmethoxybenzaldehyde by base promoted condensation reaction was reported by Kraus et al. [6] The reaction of o-arylmethoxybenzaldehyde 29 with 1.1 equiv. of phosphazene 9 in benzene or pivalonitrile at 90-100 °C gave 30 in moderate yield (Scheme 7.4). Strong ionic bases, such as LDA, LiTMP and KH, were ineffective for this cyclization reaction. 

Tyrolobibenzyls are a new class of naturally occurring bibenzyl derivatives possessing a unique phenylethyl-benzofuran skeleton. Tyrolobibenzyls A 119,... 

Benzofuran derivatives are one of the most important oxygen-containing heterocycles. Many natural or synthetic compounds containing benzofuran skeletons have been foxmd to possess remarkable activity as agrochemicals and pharmaceuticals [66]. Many methods have been developed for the synthesis of benzofuran in homogeneous and heterogeneous catalytic pathway. However, only the heterogeneously catalyzed reactions will be discussed here. 

Furans and benzofurans continue to play an important role in the field of heterocyclic chemistry because their skeletons are present in many naturally occurring molecules, and they serve also as extremely useful precursors or intermediates towards the realization of many complex molecules. The authors of the present chapter have placed their attention on the more interesting applications and syntheses of these families of compounds, instead of executing an exhaustive literature search of all the relevant papers that were recorded in 2000. 

Three groups of methods are distinguished. In the first group, the starting molecule already has the desired skeleton, the initial compound being partially reduced benzofuran 3(2H)-benzofuranone, 6,7-dihydro-4(5//)-benzofuranone, 2,3-dihydrobenzofuran, tetrahydrobenzofuran, hexahydrobenzofuran, or perhydrobenzofuran. 

Transition from a chromenoid skeleton to a benzofuran has also been achieved by other means. We may mention the photooxidation of rotenone814 and the preparation of 5,6-dirnethoxybenzofuran by electronic impact on 6,7-dimethoxycoumarin.815 The Koelsch reaction is kindred it converts couinarine into 2,3-dihydrobenzofuran derivatives.816... 

Two similar types of structures, ortho-alkoxyphenones (12.16) and benzofurans (12.17), were found to lessen multidrug resistance exhibited by tumor cells. Compounds in Hansch analyses normally share the same basic molecular skeleton. In this study of tumor cell resistance modulators, inclusion of an indicator variable allows all the data for both structural types to be pooled into one large data set. The indicator variable, /BF, is given a value of 1 if the compound is a... 

While both 2- and 3-furylcarbene complexes 99 and 103 gave [fo -annulated benzofurans (100 and 104), only the 2-pyrrolyl carbene complex 105 afforded the aromatic indole skeleton (106). In contrast, annulation of the 2,5-dimethylated 3-pyrrolylcarbene complex 107 occurred at the 4-position to give isoindole quinone 108 after oxidative work-up [82g]. 

From Cyperaceae, many quinones with the 407 skeleton (scabequinones) were isolated, among others (73TL3 78P263). Total synthesis of racemic scabequinone (407), a major component of Cyperus scaber, from a benzofuran derivative has been described (73CC718). 

The Stork group reported the synthesis of racemic codeine and thebaine utilizing the intramolecular Diels-Alder reaction as the key transformation in 2009 [45]. The key features of their synthesis are (1) a direct construction of a phenanthrofuran skeleton (A-B-C-E tetracyclic system) by the intramolecular Diels-Alder reaction of a diene tethered to the benzofuran ring and (2) a formation of the D-ring by the intramolecular SN2 reaction of an amino-mesylate. 

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