Palladium-catalyzed cross-coupling reactions of arylmetal compounds with β-substituted α-iodoenones and a cyclohexyl triflate

Boße, Folkert; Tunoori, Ashok Rao; Niestroj, AndréJ.; Gronwald, Oliver; Maier, Martin E.

doi:10.1016/0040-4020(96)00489-9

Cited by 23 publications

(14 citation statements)

References 47 publications

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“…For example, with Molt-4 leukemia cells 94b has arylboronic acid. [48,49] These results underscore the import-an IC 50 of 9·10 Ϫ5 . Electrochemical studies and also the chemical experiment led us to suspect that the oxidation might produce aryl dimers.…”

Section: Analogs Without the Nitrogen Heterocyclementioning

confidence: 64%

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Design and Synthesis of Dynemicin Analogs

Maier¹,

Boße

Niestroj

1999

Eur. J. Org. Chem.

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Dynemicin A is a member of the family of enediyne natural products. It is unique in that it combines a ten‐membered enediyne with an anthraquinone substructure. These features stimulated the development of synthetic approaches to the natural product itself and of analogs thereof. This review summarizes the total syntheses of dynemicin A. In addition, an overview of the known analogs is presented. The analogs can be classified according to the designed trigger mechanism. Most of the analogs contain a removable carbamate on the nitrogen atom. Others are quite similar to the natural lead in that they contain a quinone substructure, which upon reduction causes opening of the oxirane ring. In addition, there are analogs that contain an aromatic sector, the enediyne, and the oxirane ring but lack the nitrogen heterocycle. In these compounds the aryl ring assumes a different conformation from that in dynemicin A. Many of the simplified analogs proved to be quite active in vitro as well in vivo against murine tumor models. A highlight is compound 30 which is much more active than dynemicin A itself. However, looking at all analogs there is no clear‐cut correlation between the DNA‐cleaving ability at neutral pH and the in vitro results. From this one might conclude that there are possibly two mechanisms for antitumor activity. One involves diradical formation whereas the other might be due to a ligand‐receptor interaction.

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Section: Analogs Without the Nitrogen Heterocyclementioning

confidence: 64%

“…Therefore the synthesis was modified in such a way to even allowed the preparation of sterically hindered aryl substituted cyclohexenes. Using the cyclohexenone 84 [48] we allow for a substrate-directed epoxidation. [55] On other oc-casions we had noted that the tertiary ether function in compounds of type 101 is very sensitive to acid.…”

Section: Scheme 19mentioning

confidence: 99%

Design and Synthesis of Dynemicin Analogs

Maier¹,

Boße

Niestroj

1999

Eur. J. Org. Chem.

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“…A crude sample of lactol (18) was used in the reduction to the cyclic ether (19). Treatment with triethylsilane and trifluoroacetic acid in dichloromethane at −78 • C for 3 h resulted in recovered starting material.…”

Section: Resultsmentioning

confidence: 99%

“…Treatment with triethylsilane and trifluoroacetic acid in dichloromethane at −78 • C for 3 h resulted in recovered starting material. However, addition of a catalytic amount of boron trifluoride diethyl etherate afforded cyclic ether (19) in 0· 5 h. Formation of by-products became evident by t.l.c. if more boron trifluoride diethyl etherate was added or the reaction time was increased.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of 8-Bromokalafungin as an Intermediate for the Preparation of C-Glycoside Derivatives

Brimble¹,

Nairn²,

Prabaharan³

et al. 1997

Aust. J. Chem.

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The preparation of 8-bromokalafungin (20) which is a key intermediate for the synthesis of C-glycoside containing pyranonaphthoquinone antibiotics related to medermycin (6) is described. Although attempts to selectively monobrominate kalafungin (1) at C8 were unsuccessful, 8,10-dibromokalafungin (21) was prepared by using excess N-bromosuccinimide in chloroform. Selective bromination at C6 on a naphthalene ring was achieved upon treatment of naphthol (9) with N-bromosuccinimide (1 equiv.). Conversion of naphthol (9) into naphthoquinone (15) was effected by methylation, Baeyer–Villiger oxidation, acetylation via a Fries rearrangement and oxidation with ceric ammonium nitrate. Conversion of the 7-bromo quinone (15) into 8-bromokalafungin (20) proceeded through subsequent addition of 2-trimethylsilyloxyfuran (16) followed by oxidative rearrangement of the resultant furonaphthofuran (17) to furonaphthopyran (18). After reduction of the lactol (18) to cis ether (19), demethylation and epimerization at C5 with boron tribromide afforded 8-bromokalafungin (20). 8-Bromokalafungin (20) failed to undergo Pd(0)-mediated cross-coupling reactions with the stannyl glucal (22).

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“…The Stille coupling, finally, of the aryl stannane 5c with 3 gave the best results. We used conditions that had been advantageous in our hands for the coupling of α-iodoenones with aryl metal compounds [15]. That is, use of the relatively stable Pd 2 (dba) 3 .…”

Section: ____________________________________________________________mentioning

confidence: 99%

Synthesis of a Tetrasubstituted Cyclohexene from a Bicyclo[2.2.2]octa-2,5-diene

Boße

Maier

2000

J. prakt. Chem.

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Polysubstituted cyclohexanes and -hexenes represent important substructures in a number of natural products. Among several strategies for synthesizing such compounds, the tactical combination of a Diels-Alder reaction between a cyclic 1,3-diene and a suitable dienophile followed by cleavage of the bicyclic structure has been widely used [1]. As a consequence the stereochemistry of the two substituents that originate from cleavage of the bridge are cis to each other. This structural situation can be found, for example in the E-ring of the antitumor antibiotic dynemicin A [2,3]. The known total syntheses of dynemicin A have addressed this issue in different ways [4 -8]. In the course of the synthesis of analogs [9] of dynemicin A (Scheme 1) we planned to use the above mentioned strategy for establishing the array of rings spanning C-E. One of the two functional groups resulting from the cleavage of the Keywords: Cross-coupling, Cycloadditions, Ozonolysis, Dynemicin, Ring cleavage Abstract. A palladium-catalyzed cross-coupling reaction between the arylstannane 5c and the bicyclic vinyl bromide 3, which was obtained by a Diels-Alder reaction, provided the substituted bicyclo[2.2.2]octa-2,5-diene 6. A subsequent ozonolysis of the less substituted double bond of 6 followed bridge will be transformed to a methyl group, while the other one would be used to fashion the enediyne (cf. structures A and B). In this paper, we report on initial studies in this direction resulting in the cyclohexene 8.As a dienophile methyl 3-bromopropiolate (2) was used [10]. This was converted to the bicyclic vinyl bromide 3 by a Diels-Alder reaction [11]. The problem in subsequent functionalization reactions of 3 is the possible aromatization reaction through a retro Diels-Alder reaction with the elimination of ethylene. For the substitution of the bromide with an aryl group the aryl metal derivatives 5a -c were prepared from the bromide 4 [12, 13] (Scheme 2). The corresponding zinc derivative 5a was not isolated and used directly [yield not determined (ND)] [14].

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Palladium-catalyzed cross-coupling reactions of arylmetal compounds with β-substituted α-iodoenones and a cyclohexyl triflate

Cited by 23 publications

References 47 publications

Design and Synthesis of Dynemicin Analogs

Design and Synthesis of Dynemicin Analogs

Synthesis of 8-Bromokalafungin as an Intermediate for the Preparation of C-Glycoside Derivatives

Synthesis of a Tetrasubstituted Cyclohexene from a Bicyclo[2.2.2]octa-2,5-diene

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