Formal synthesis of (−)-agelastatin A: an iron(II)-mediated cyclization strategy

• Daisuke Shigeoka,
• Takuma Kamon and
• Takehiko Yoshimitsu

Beilstein J. Org. Chem. 2013, 9, 860–865, doi:10.3762/bjoc.9.99

• have developed a new approach to key compounds 5a/5b for (−)-agelastatin A (1) synthesis, which features the iron(II)-mediated radical cyclization of N-tosyloxycarbamate, a safe azidoformate surrogate. Although somewhat moderate chemical yields of the compounds were obtained in this study, the

Direct alkenylation of indolin-2-ones by 6-aryl-4-methylthio-2H-pyran-2-one-3-carbonitriles: a novel approach

• Sandeep Kumar,
• Ramendra Pratap,
• Abhinav Kumar,
• Brijesh Kumar,
• Vishnu K. Tandon and
• Vishnu Ji Ram

Beilstein J. Org. Chem. 2013, 9, 809–817, doi:10.3762/bjoc.9.92

• hydride-AIBN initiated radical cyclization [33][34]. In 2005, Player and co-workers reported a tandem Heck/Suzuki–Miyaura coupling process for the synthesis of (E)-3,3-(diaryl)oxindoles [35][36][37]. Recently, alkenylation of indolin-2-ones has been developed by palladium-catalyzed aromatic C–H activation

Recent advances in transition-metal-catalyzed intermolecular carbomagnesiation and carbozincation

• Kei Murakami and
• Hideki Yorimitsu

Beilstein J. Org. Chem. 2013, 9, 278–302, doi:10.3762/bjoc.9.34

• ]. As a result, Hoveyda’s zirconium-catalyzed reactions provided homobenzylmagnesium intermediates 4j, while Kambe’s titanium-catalyzed reactions afforded benzylmagnesium intermediates 4k. Kambe applied the titanocene-catalyzed reaction to a three-component coupling reaction involving a radical

• cyclization reaction (Scheme 44). Under Nakamura’s iron-catalyzed carbometalation reaction conditions (shown in Scheme 17), the reaction of oxabicyclic alkenes provided ring-opened product 4m through a carbomagnesiation/elimination pathway (Scheme 45, reaction 4l to 4m) [82]. In contrast, the use of the 1,2

Radical zinc-atom-transfer-based carbozincation of haloalkynes with dialkylzincs

• Fabrice Chemla,
• Florian Dulong,
• Franck Ferreira and
• Alejandro Pérez-Luna

Beilstein J. Org. Chem. 2013, 9, 236–245, doi:10.3762/bjoc.9.28

• alkyl iodides in the presence of Me2Zn/O2 with β-(propargyloxy)enoates entails the intramolecular carbometallation of the pendant alkynes substituted by silyl, alkyl, aryl, alkenyl or amino groups by a 5-exo dig radical cyclization step [37][38]. Intermolecular carbozincation of terminal arylacetylenes

Hybrid super electron donors – preparation and reactivity

• Jean Garnier,
• Douglas W. Thomson,
• Shengze Zhou,
• Phillip I. Jolly,
• Leonard E. A. Berlouis and
• John A. Murphy

Beilstein J. Org. Chem. 2012, 8, 994–1002, doi:10.3762/bjoc.8.112

• mixture of 32 [35], the product of aryl radical cyclization, (74%), together with recovered 30 (6%) and deiodinated but uncyclised product 31 (12%). This is the first observation of efficient aryl radical generation at room temperature from a super-electron-donor. For comparison, less than 1% yield of 32

Tandem catalysis of ring-closing metathesis/atom transfer radical reactions with homobimetallic ruthenium–arene complexes

• Yannick Borguet,
• Xavier Sauvage,
• Guillermo Zaragoza,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2010, 6, 1167–1173, doi:10.3762/bjoc.6.133

• was required to perform the radical cyclization of this cyclohexenyl trichloroacetamide, presumably due to the unfavorable disposition of the trichloromethyl unit and the endocyclic double bond in the most stable rotamer of the amido group [11]. Hence, this preliminary experiment allowed us to

• that adding a benzyl or tosyl group to the amide functionality of compound 5 facilitated its radical cyclization mediated by complex 3. Replacing the trichloroacetamide moiety with the corresponding tribromoacetamide unit was also found to enhance the Kharasch reactivity [11]. Thus, we synthesized four

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

• base generates the styrene 107 and oxalic acid. 4.2. Vedejs. Anionic Michael addition This strategy is very similar to Ziegler’s preceding approach since both share the same method for forming the C3–N4 bond and aim at constructing the C1–C9a bond. But while Ziegler uses a tandem radical cyclization

• developments have been reported on this series of compounds. 4.4. Jones. Radical cyclization A radical cyclization was used by the Jones group for the formation of smaller rings via a 5-exo-dig radical cyclization. Bromoalkyne 118 was chosen to construct pyrrolo[1,2-a]indole 119. The reaction was initiated

• ) [114]. 5.4. Parson. Radical cyclization The development of novel cascade (or domino) radical reactions is an active area of current research, and one approach to the mitomycin ring system focused on the application of 1-6-hydrogen atom transfer to create a pyrrolidinone radical, which could then

Reduction of arenediazonium salts by tetrakis(dimethylamino)ethylene (TDAE): Efficient formation of products derived from aryl radicals

• Mohan Mahesh,
• John A. Murphy,
• Franck LeStrat and
• Hans Peter Wessel

Beilstein J. Org. Chem. 2009, 5, No. 1, doi:10.3762/bjoc.5.1

• )]. We expected that the aryl radical 53a generated by the reduction of arenediazonium salt 49a by TDAE would undergo 5-exo-trig radical cyclization onto the vinyl bromide to afford the alkyl radical intermediate 54a, from which Br• would be eliminated to afford the exocyclic alkene 50a (Scheme 6). Such

• electron donor. Additionally, we have described the utility of the aryl radicals in the construction of indolines and indoles by intramolecular radical cyclization of aryl radicals onto appropriately placed alkenes bearing terminal radical leaving groups. The presence of a suitable radical leaving group

• like a sulfide, sulfoxide or sulfone is necessary for the self-termination of the 5-exo-trig radical cyclization reactions to avoid competing intermolecular radical side-reactions. The TDAE-mediated radical-based addition-elimination route for the construction of indole ring systems warranted anhydrous

Recent progress on the total synthesis of acetogenins from Annonaceae

• Nianguang Li,
• Zhihao Shi,
• Yuping Tang,
• Jianwei Chen and
• Xiang Li

Beilstein J. Org. Chem. 2008, 4, No. 48, doi:10.3762/bjoc.4.48

Sordarin, an antifungal agent with a unique mode of action

• Huan Liang

Beilstein J. Org. Chem. 2008, 4, No. 31, doi:10.3762/bjoc.4.31

• believed to involve single-electron oxidation of the cyclopropanol, fragmentation of a transient radical cation, and diastereoselective radical cyclization. In the enantioselective synthesis, this transformation was more efficiently achieved by treatment of enantioenriched 41b with the AgNO3-ammonium

• persulfate-pyridine system [32]. The ensuing Ag(I) catalyzed oxidative radical cyclization proceeded in 85% yield. Racemic ketone 43 underwent regio- and stereoselective allylation under Corey-Enders conditions to provide olefin 44, which was subjected to Lemieux-Johnson cleavage to corresponding aldehyde

Do α-acyloxy and α-alkoxycarbonyloxy radicals fragment to form acyl and alkoxycarbonyl radicals?

• Dennis P. Curran and
• Tiffany R. Turner

Beilstein J. Org. Chem. 2006, 2, No. 10, doi:10.1186/1860-5397-2-10

• us to suggest that some radicals in the Wille cascade progress to products by oxidation or group transfer rather than β-fragmentation. Results and Discussion We choose to generate the candidate radicals for fragmentation by a radical cyclization rather than by a standard atom or group abstraction

• radical cyclization of enol ether 11a with tributyltin hydride (0.1 M) followed by chromatographic purification provided 14a in 95% yield as an inseparable 1:2 mixture of exo and endo isomers. Likewise, cyclization of enol ester 11b provided a 1:2 mixture of 14b-exo and 14b-endo in 68% isolated yield. The

• concentrations, complete conversion of 11b was observed and reduced product 14b was formed in good yield. None of the directly reduced product 18b was observed even at the highest concentration, indicating that the intermediate radical cyclization is fast (kC > 106 s-1). Negligible amounts of ketone 15 (≤ 2