Planned and unplanned halogenations in route to selected oroidin alkaloids

Wang, Shaohui; Dilley, Anja S.; Poullennec, Karine G.; Romo, Daniel

doi:10.1016/j.tet.2006.01.115

Cited by 46 publications

(42 citation statements)

References 45 publications

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“…[26] Communications this missing key peak, enough information could be derived from the other interproton distances of H11, H12, H17, and H18 to assign the relative configuration of the azabicyclo-[3.3.0]octane moiety without needing direct information for the fusion of the two five-membered rings. Biosynthetically, the core structures of tetrabromostyloguanidine (1), axinellamine A (8), and massadine (9, Scheme 3) [29] could be derived from the same pathway, [30] and therefore an identical configuration at C17 is probable. The research group of Baran recently proposed that sceptrin (6) is the biosynthetic precursor to axinellamine A (8) as well as to the palauamines (2).…”

Section: Methodsmentioning

confidence: 99%

Structural Assignment of Tetrabromostyloguanidine: Does the Relative Configuration of the Palau'amines Need Revision?

2007

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Section: Methodsmentioning

confidence: 99%

Structural Assignment of Tetrabromostyloguanidine: Does the Relative Configuration of the Palau'amines Need Revision?

2007

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“…[33] The coupling/cyclization sequence outlined here represents a novel approach to halogenated spirocycles. [34] In summary, described herein are the unique, high yielding, and diastereoselective coupling reactions involving sulfonium ylide intermediates from halogenated vinyl diazoacetates and 2-thioindoles. These transformations led to the synthesis of structurally interesting substrates that would be difficult to prepare by using other methodologies.…”

Section: Scheme 4 (E)-chlorovinyldiazoacetate Couplingmentioning

confidence: 95%

Highly Diastereoselective Sulfonium Ylide Rearrangements to Quaternary Substituted Indolines

2008

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The stereoselective generation of quaternary centers, including quaternary centers at C3 of oxindoles and indolines, remains a challenge for contemporary organic synthesis.[1] To date, a list of the most successful methods addressing the indoline/oxindole problem would include intra-and intermolecular Mannich, [2] Heck, [3] and Mukaiyama aldol condensations, [4] as well as alkylation reactions, [5][6][7] cycloadditions, [8] pallyl couplings, [9] cyclopropane ring openings, [10] oxidative couplings, and rearrangements. [11,12] In the course of our studies aimed at the use of 2-thioindoles as precursors to substituted oxindoles and indolines, [13][14][15] we became fascinated with the coupling of 2-thio-3-alkylindoles with vinyl diazoacetates in the presence of Rh II salts because the reaction delivered structurally rich quaternary substituted indolines in high yield and the mechanism was mechanistically interesting (Scheme 1).[16] We did not use this reaction in total synthesis endeavors because it was only modestly diastereoselective when monosubstituted vinyl diazoacetates were used as the coupling partners. [17,18] In terms of the mechanism for the transformation to 3 and 4, an abundance of indirect evidence suggested a [3,3] rearrangement of an intermediate sulfonium ylide (i.e. 7 or 8 to give 9 and 10, Scheme 2).[19] Because of the well-established stability of sulfonium ylides, we presumed that Rh II was important in the generation and delivery of the carbenoid to the thioether, but that it was absent during the subsequent sequence leading to CÀC bond formation and 10 (cf. 7, R'' = CC, Scheme 2). [20] Our previous studies resulted in levels of diastereoselectivity that were similar to those seen with 1, therefore we were surprised when the reaction of bis(thioindole) 11 [21] with 2 gave 12 in relatively high diastereoselectivity (Scheme 3). We became intrigued by the generation of 12 and decided to examine the reaction in more detail by exploring the effect of thioindole substitution on diastereoselectivity. As an aside, the importance of the thioether group in the reaction becomes Scheme 1. 2-Thioindole Rh II -vinyl carbenoid couplings.Scheme 2. Working hypothesis for 2-thioindole Rh II -vinyl carbenoid couplings.Scheme 3. Diastereo-and chemoselective bis(indole) vinyl carbenoid couplings.

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“…Oxidative tetracyclization starting from compound 68 was successful using the Stang reagent, PhI(CN)OTf, with formation of the key N12-C4 and N9-C5 bonds. Further oxidation mediated by CAN led straightforwardly to dibromophakellstatin (69). The conversion of 69 into dibromophakellin (7) was finally achieved by enol ether formation with Meerwein's reagent and amination using ammonium propionate.…”

Section: Dibromophakellin (7) and Dibromophakellstatin (69)mentioning

confidence: 99%

Biomimetic Synthesis of Marine Pyrrole‐2‐Aminoimidazole and Guanidinium Alkaloids

Appenzeller

Al‐Mourabit

2011

Biomimetic Organic Synthesis

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Planned and unplanned halogenations in route to selected oroidin alkaloids

Cited by 46 publications

References 45 publications

Structural Assignment of Tetrabromostyloguanidine: Does the Relative Configuration of the Palau'amines Need Revision?

Structural Assignment of Tetrabromostyloguanidine: Does the Relative Configuration of the Palau'amines Need Revision?

Highly Diastereoselective Sulfonium Ylide Rearrangements to Quaternary Substituted Indolines

Biomimetic Synthesis of Marine Pyrrole‐2‐Aminoimidazole and Guanidinium Alkaloids

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