Abstract:A synthesis fit for a king: The total synthesis of (±)‐kingianins A, D, and F has been achieved in ten steps. Key features include the gram‐scale synthesis and partial reduction of a conjugated tetrayne to a (Z,Z,Z,Z)‐tetraene, the domino 8π–6π electrocyclic ring closure of a (Z,Z,Z,Z)‐tetraene, and the radical‐cation‐catalyzed formal Diels–Alder dimerization of functionalized bicyclo[4.2.0]octadiene precursors.
“…[115] The reduction of tetrayne 289 was carried out with the use of Rieke nickel in ethanol and the resulting (Z,Z,Z,Z)-tetraene 290 was in situ used for further reaction (Scheme 24). The synthetic route which included reduction of tetrayne is a key step allowed to obtain precursors of previously synthetically unavailable Kinginians A, D and F, natural products isolated from Endiandra kingiana.…”
Section: Reduction Of Polyynes As a Synthetic Tool In Natural Productmentioning
Polyynes are linear carbon rods that may be regarded as models of carbyne – still elusive linear allotropic form of carbon. This microreview addresses the use of polyynes as synthetic precursors of complex organic and organometallic compounds. Application of such unusual molecules as starting materials for various chemical transformations leads to products which often are not easily accessible using “traditional“ approaches. Polyynes may for instance be used in the synthesis of molecular wires, materials possessing high nonlinear optical response, complex donor–acceptor systems, solvatochromic fluorescent dyes or natural products. The most significant challenge here is to control the regioselectivity of a transformation of such linear sp‐hybridized carbon chains. The impact of steric and electronic properties of reagents on the reaction pattern is hence highly important and will be discussed. Moreover, the transformations of end‐groups will also be addressed since their reactivity might very often be different than that of acetylenes.
“…[115] The reduction of tetrayne 289 was carried out with the use of Rieke nickel in ethanol and the resulting (Z,Z,Z,Z)-tetraene 290 was in situ used for further reaction (Scheme 24). The synthetic route which included reduction of tetrayne is a key step allowed to obtain precursors of previously synthetically unavailable Kinginians A, D and F, natural products isolated from Endiandra kingiana.…”
Section: Reduction Of Polyynes As a Synthetic Tool In Natural Productmentioning
Polyynes are linear carbon rods that may be regarded as models of carbyne – still elusive linear allotropic form of carbon. This microreview addresses the use of polyynes as synthetic precursors of complex organic and organometallic compounds. Application of such unusual molecules as starting materials for various chemical transformations leads to products which often are not easily accessible using “traditional“ approaches. Polyynes may for instance be used in the synthesis of molecular wires, materials possessing high nonlinear optical response, complex donor–acceptor systems, solvatochromic fluorescent dyes or natural products. The most significant challenge here is to control the regioselectivity of a transformation of such linear sp‐hybridized carbon chains. The impact of steric and electronic properties of reagents on the reaction pattern is hence highly important and will be discussed. Moreover, the transformations of end‐groups will also be addressed since their reactivity might very often be different than that of acetylenes.
“…It has played a central role in the development of reactivity theory, [1][2][3] and has enjoyed a great number of elegant and creative applications in both the academic and industrial setting. [4][5][6][7][8] Despite almost a century of research, [9] the DA reaction remains a highly active area of study, and current fields of interest include the development of new catalytic asymmetric reactions, [10] incorporation of DA reactions into domino sequences, [11,12] the elucidation of natural product biosyntheses, [13][14][15][16][17] and the development of diene-transmissive DA reactions. [18][19][20][21][22] Although the DA reaction has been used to access a vast array of structural motifs, the reaction is not without limitation.…”
The Diels-Alder reaction is one of the most powerful, well-established, and versatile reactions in organic chemistry; however, its application in certain settings remains a challenge as a result of functional group incompatibility. In this review, we examine the methods in which masked ketenes can be employed as dienophiles, taking particular note of applications in complex settings.
“…The spirocyclic core of the ramonanins is unprecedented among natural products and Schroeder and co-workers proposed a biosynthetic pathway that involved dimerization of a lignan precursor, 7, through a "Diels-Alder-like mechanism" (Scheme 1 b). [11] We considered that the ramonanins A-D (3-6) might also be the result of a biosynthetic RCDA dimerization. There are no reports of 1,2-dimethylenecyclopentane-type structures undergoing Diels-Alder dimerizations under ambient conditions.…”
mentioning
confidence: 99%
“…[10] Our previous studies on the kingianin natural products utilized a radical-cation-catalyzed formal Diels-Alder (RCDA) reaction to dimerize a thermally unreactive bicyclo[4.2.0]octadiene structure. [11] We considered that the ramonanins A-D (3-6) might also be the result of a biosynthetic RCDA dimerization. [12] To investigate the nature of this fascinating biosynthetic dimerization we chose to pursue a total synthesis of the ramonanin natural products (3)(4)(5)(6).…”
The first total synthesis of the ramonanin family of lignan natural products is described. The short synthesis involves a 2,5-diaryl-3,4-dimethylene tetrahydrofuran intermediate, which participates in an unexpectedly facile Diels-Alder dimerization, generating all four natural products. Insights into the reactivity and stereoselectivity of the key dimerization are provided through computational studies employing B3LYP/6-31G(d) and M06-2X/6-31G(d) model chemistries.
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