Novel 7- and 8-Endo 2-Indolylacyl Radical Cyclizations:  Efficient Construction of Azepino- and Azocinoindoles

Bennasar, M.‐Lluïsa; Roca, and Tomàs; García-Díaz, Davinia

doi:10.1021/jo070322m

Cited by 28 publications

(7 citation statements)

References 23 publications

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“…However, after implementing this approach, an undesirable isomer was obtained [ 21 ]. Although a number of acid- [ 22 – 23 ] and metal-catalysed cascade processes [ 24 – 25 ] have been developed (for example, Pictet–Spengler [ 26 ] and Ugi-type reactions [ 27 ], the acyl radical cyclisations [ 28 ] and the 1,7-electrocyclisation of azomethine ylides or ring expansion sequences [ 29 ]), most of these approaches are ineffective for synthesising pyrrolo[3,2- c ]azepines. Recently, Echavarren and Beller reported a novel Au- or Pt-catalysed cycloisomerisation reaction of pyrrole-2-carboxamides that produces pyrrolo[2,3- c ]- and [2,3- d ]azepinones [ 30 – 31 ].…”

Section: Introductionmentioning

confidence: 99%

Unprecedented nucleophile-promoted 1,7-S or Se shift reactions under Pummerer reaction conditions of 4-alkenyl-3-sulfinylmethylpyrroles

Go¹,

Morimatsu²,

Wasada³

et al. 2018

Beilstein J. Org. Chem.

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A unique 1,7-S- and Se-shift reaction under Pummerer reaction conditions of 4-alkenyl-3-sulfinyl- and seleninylpyrroles was described. The usual Pummerer reaction of 4-(alkenylaminomethyl)-3-phenylsulfinylpyrroles and a successive reaction with tetrabutylammonium hydroxide (TBAH) yielded either pyrrolo[3,2-c]azepines or N-pyrrol-3-ylmethyl-N-(4-hydroxy-3-sulfanylpropyl)-p-toluenesulfonamides (diols). Seleno-Pummerer reactions of 3-selanylmethylpyrroles also proceeded via in situ generation of selenoxides, followed by a treatment with TBAH.

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Section: Introductionmentioning

confidence: 99%

Unprecedented nucleophile-promoted 1,7-S or Se shift reactions under Pummerer reaction conditions of 4-alkenyl-3-sulfinylmethylpyrroles

Go¹,

Morimatsu²,

Wasada³

et al. 2018

Beilstein J. Org. Chem.

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“…Theoretical calculations by Beckwith and Schiesser predicted that the 8- endo cyclization of 7-octenyl radical is preferred over the corresponding 7- exo cyclization . The 8- endo cyclizations of various types of radicals, − including alkyl, aryl, acyl, ketyl, and even amidyl radicals, were later implemented with variable efficiencies and regioselectivities. Of particular concern was the cyclization of α-ester radicals, − especially those leading to the synthesis of heptanolactones. − Literature reports revealed that the 8- endo cyclization is fundamentally preferred over the corresponding 7- exo cyclization for α-ester radicals.…”

Section: Introductionmentioning

confidence: 99%

Efficient Regio- and Stereoselective Formation of Azocan-2-ones via 8-Endo Cyclization of α-Carbamoyl Radicals

Fang

Liu

2010

J. Am. Chem. Soc.

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The iodine-atom-transfer 8-endo cyclization of alpha-carbamoyl radicals was investigated experimentally and theoretically. With the aid of Mg(ClO(4))(2) and a bis(oxazoline) ligand, N-ethoxycarbonyl-substituted N-(pent-4-enyl)-2-iodoalkanamides underwent 8-endo cyclization leading to the formation of only the corresponding 3,5-trans-substituted azocan-2-ones in excellent yields. Similarly, the BF(3).OEt(2)/H(2)O-promoted reactions of N-ethoxycarbonyl-N-(2-allylaryl)-2-iodoalkanamides afforded exclusively the benzazocanone products with a 3,5-cis configuration in high yields. The bidentate chelation of substrate radicals not only significantly improved the efficiency of cyclization but also resulted in the change of stereochemistry of azocanone products from 3,8-trans to 3,8-cis. Theoretical calculations at the UB3LYP/6-31G* level revealed that the cyclization of N-carbonyl-substituted alpha-carbamoyl radicals occurs via the E-conformational transition states without the presence of a Lewis acid. On the other hand, the cyclization proceeds via the Z-conformational transition states when the substrates form the bidentate chelation with a Lewis acid. In both cases, the 8-endo cyclization is always fundamentally preferred over the corresponding 7-exo cyclization. The complexed radicals having the more rigid conformations also allow the better stereochemical control in the iodine-atom-abstraction step. To further understand the reactivity of alpha-carbamoyl radicals, the competition between the 8-endo and 5-exo cyclization was also studied. The results demonstrated that the 8-endo cyclization is of comparable rate to the corresponding 5-exo cyclization for alpha-carbamoyl radicals with fixed Z-conformational transition states. As a comparison, the 8-endo mode is fundamentally preferred over the 5-exo mode in the cyclization of NH-amide substrates because the latter requires the Z-conformational transition states, whereas the former proceeds via the more stable E-conformational transition states.

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“…Bennasar and coworkers disclosed 38 that the presence in starting material of the carbamate nitrogen had positive effect on the azepinoindole formation (11% (+ 62% 1048a) and 29% (+ 45% 1048b), respectively). As expected, the cyclization could be controlled by vinylic bromine: radical cyclization of selenoester 1046c provided azepinoindole 1047c as the major product (62% + 19% 1048c).…”

Section: Other Studiesmentioning

confidence: 99%

Recent developments in syntheses of the post-secodine indole alkaloids. Part III: Rearranged alkaloid types

Hájíček¹

2011

Collect. Czech. Chem. Commun.

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The third part of a planned review on developments in the field of total and formal total synthesis of the post-secodine indole alkaloids focuses on types of rearranged alkaloids, i.e. on the skeletons with altered connectivities next to the indol(e)ine moiety, especially with a new bond to N-1. It reviews the synthesis of melodane, goniomitine, chippiine/dippinine, lirofoline and tronocarpine alkaloids, as well as alkaloids of secoschizozygane/vallesamidine, schizozygane and isoschizozygane type. It covers the literature from approximately 1991 up to May 2011. A review with 115 references.

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Novel 7- and 8-Endo 2-Indolylacyl Radical Cyclizations: Efficient Construction of Azepino- and Azocinoindoles

Cited by 28 publications

References 23 publications

Unprecedented nucleophile-promoted 1,7-S or Se shift reactions under Pummerer reaction conditions of 4-alkenyl-3-sulfinylmethylpyrroles

Unprecedented nucleophile-promoted 1,7-S or Se shift reactions under Pummerer reaction conditions of 4-alkenyl-3-sulfinylmethylpyrroles

Efficient Regio- and Stereoselective Formation of Azocan-2-ones via 8-Endo Cyclization of α-Carbamoyl Radicals

Recent developments in syntheses of the post-secodine indole alkaloids. Part III: Rearranged alkaloid types

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