Total Synthesis of Kingianins A, D, and F

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.

Reactivity of Polyynes: Complex Molecules from Simple Carbon Rods

“…[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.…”

Masked Ketenes as Dienophiles in the Diels–Alder Reaction

“…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.…”

Total Synthesis of Ramonanins A–D

“…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.…”

“…[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).…”