Total Synthesis of Ramonanins A–D

Abstract

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.

Synform Issue 2017/07

“…Subsequent low-temperature NMR studies not only identified the structure of the imine sulfonium I but also witnessed its robust formation and its extreme instability (Scheme 3). We further investigated the reaction by using DFT calculations and found that the reaction could be divided into three essential steps, including electrophilic assembling, deprotonation, and [3,3]-sigmatropic rearrangement." Professor Peng added: "The reaction also proved to be applicable to a wide range of aryl sulfoxides and alkyl nitriles (Scheme 4).…”

Synform Issue 2017/07

“…By investigating and mimicking these natural processes in vitro we hope to make important discoveries concerning how the breaking of symmetry can be better exploited in synthesis. (Figure 1a), 2,3 redox ca talysis (Figure 1b), 4,5 and domino reaction sequences ( Figure 1c). [5][6][7][8][9] Figure 1 Natural product targets synthesized by the Lawrence group…”

Nonclassical Mechanism in the Cyclodehydration of Diols Catalyzed by a Bifunctional Iridium Complex

“…NHC–Ir complexes (NHC=N‐heterocyclic carbene) have proven to be excellent catalysts in numerous processes, particularly in dehydrogenations and transfer hydrogenations . ,,, NHCs can be relatively easily functionalized to provide the desired reactivity. Their versatility has recently been highlighted by Peris in a recent review article, in which the author refers to NHCs as “smart ligands”.…”