β- and γ-lactams by nickel powder mediated 4-exo or 5-endo radical cyclisations. A concise construction of the mesembrine skeleton

Cassayre, Jérôme; Quiclet‐Sire, Béatrice; Saunier, Jean-Baptiste; Zard, Samir Z.

doi:10.1016/s0040-4020(97)10204-6

Cited by 60 publications

(24 citation statements)

References 41 publications

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“…The latter undergoes a 5‐ endo cyclization to afford IIa , which is readily oxidized to give acyl iminium intermediate III . Similar results were observed by Zard , but under very different reaction conditions, in which the oxidizing agent was believed to be the starting trichloroacetamide 2a . Although two oxidizing pathways are possible, the oxidation step probably proceeds through an electron transfer rather than the alternative chlorine atom transfer.…”

Section: Resultssupporting

confidence: 79%

“…Prior to our initial report in this field, the radical cyclization of a trichloroacetamide embedded in an enamide structure, providing hydroindoles with a methyl group at the ring junction ( Scheme ), had only been described by Zard . Parsons reported the cyclization of a dichloroacetamide with a methoxycarbonyl at the α ‐position, using either CuCl in an atom transfer radical cyclization (ATRC) or Mn(OAc) 3 in an oxidative procedure .…”

Section: Introductionmentioning

confidence: 99%

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Synthesis of Azabicyclic Building Blocks for Daphniphyllum Alkaloid Intermediates Featuring N‐Trichloroacetyl Enamide 5‐endo‐trig Radical Cyclizations

Jansana

Coussanes

Diaba

et al. 2019

Helvetica Chimica Acta

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A general procedure is reported for the synthesis of cis ring fused azapolycyclic compounds bearing an all‐carbon quaternary stereocenter at the ring fusion and an adequate functionalization for the assembly of new rings leading to advanced synthetic intermediates for Daphniphyllum alkaloid synthesis. The key carbon−carbon bond‐forming step in this approach is a radical cyclization of an N‐cycloalkenyl trichloroacetamide derivative involving a tetrasubstituted enamide to achieve polyfunctionalized lactams.

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Section: Resultssupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Synthesis of Azabicyclic Building Blocks for Daphniphyllum Alkaloid Intermediates Featuring N‐Trichloroacetyl Enamide 5‐endo‐trig Radical Cyclizations

Jansana

Coussanes

Diaba

et al. 2019

Helvetica Chimica Acta

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“…A further synthetically valuable observation is the behaviour of ene-trichloroacetamides such as 160 (Scheme 30) [70]. In this system, the intermediate radical 161 undergoes a 5- endo cyclisation into the easily oxidised tertiary radical 162 , which is then logically converted into cationic species 163 by electron transfer to the starting trichloroacetamide 160 .…”

Section: Reviewmentioning

confidence: 99%

“…Thus, a second chlorine atom is lost through reduction and the last is simply eliminated as chloride to give diene 165 as the final product. In the presence of cupric acetate additive, which somehow slows down the reduction, the elimination of chloride is faster than reduction, and it is chlorodiene 166 that is ultimately formed [70]. Since HCl is formally produced in these transformations, the addition of sodium acetate to buffer the medium is often beneficial.…”

Section: Reviewmentioning

confidence: 99%

Some aspects of radical chemistry in the assembly of complex molecular architectures

Quiclet‐Sire¹,

Zard²

2013

Beilstein J. Org. Chem.

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SummaryThis review article describes briefly some of the radical processes developed in the authors’ laboratory as they pertain to the concise assembly of complex molecular scaffolds. The emphasis is placed on the use of nitrogen-centred radicals, on the degenerate addition–transfer of xanthates, especially on its potential for intermolecular carbon–carbon bond formation, and on the generation and capture of radicals through electron transfer processes.

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“…One example has been described within the context of an approach to the ABC-ring system of manzamine A [47]. This nickel-mediated cyclization-oxidation chemistry has also been used in model studies directed toward (+)-mesembrine [52]. 22) [48].…”

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confidence: 99%

Radical Cyclizations in Alkaloid Synthesis

Hart¹

2001

Radicals in Organic Synthesis

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Over twenty years ago, my research group became interested in free-radical cyclization chemistry because we were impressed with the efficiency of a 5-hexenyl radical cyclization which we used to prove the stereochemistry of a product derived from an N-acyliminium ion cyclization [ 1, 21. A survey of the literature suggested that, at that time, free-radical cyclizations had been well developed for the preparation of carbocyclic materials, but the use of such reactions in heterocycle synthesis was not well developed. As one can see from the wealth of information that appears in Radicals in Organic Synthesis, we were clearly mistaken in our judgement of the state of the field relative to carbocycles. Nonetheless, it was this point of view that prompted us to pursue a research program designed to develop free radical cyclization reactions for use in alkaloid synthesis. Since the onset of our program [3, 41, this field has expanded enormously. This chapter will review progress in the area with certain limitations. The major focus will be on intramolecular carbon-carbon bond-forming reactions, and the chapter will be organized largely according to the type of free radical cyclization featured in the synthesis. Intermolecular free-radical reactions and cyclizations involving carbon-heteroatom bond-forming reactions will be mentioned only in passing. Although emphasis will be placed on free radical cyclization chemistry, additional details will be described in an attempt to provide the reader with an overview of each synthesis. Whereas we recognize that the inherent value of a synthesis may lie in the methodology, there is no question that chemists judge syntheses in part by their length, and this information will therefore be provided in most instances. Finally, the focus will be on completed syntheses, and only a few model studies will be presented. a-Acylamino and a-Amino Radical CyclizationsOur own efforts began with failure. Inspired by the radical addition-atom transfercyclization-fragmentation sequence reported by Heiba (Eq. 1) [ 51, we attempted the Radicals in Organic Synthesis Edited by Philippe Renaud and Mukund P. Sibi

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β- and γ-lactams by nickel powder mediated 4-exo or 5-endo radical cyclisations. A concise construction of the mesembrine skeleton

Cited by 60 publications

References 41 publications

Synthesis of Azabicyclic Building Blocks for Daphniphyllum Alkaloid Intermediates Featuring N‐Trichloroacetyl Enamide 5‐endo‐trig Radical Cyclizations

Synthesis of Azabicyclic Building Blocks for Daphniphyllum Alkaloid Intermediates Featuring N‐Trichloroacetyl Enamide 5‐endo‐trig Radical Cyclizations

Some aspects of radical chemistry in the assembly of complex molecular architectures

Radical Cyclizations in Alkaloid Synthesis

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