Divergent Total Synthesis of Taiwaniaquinones A and F and Taiwaniaquinols B and D

Abstract

A divergent approach was developed toward the total synthesis of taiwaniaquinoids. An advanced intermediate 5a with trans A/B ring junction was concisely assembled by employing a Bi(OTf)3-catalyzed cationic cyclization and a Wolff-type ring contraction as key steps. This common intermediate was readily converted to racemic taiwaniaquinones A and F and taiwaniaquinols B and D, respectively.

The Photo‐Nazarov Reaction: Scope and Application

“…In contrast to the conventional acid-catalyzed methods, this photolytic electrocyclization proceeds under neutral or basic conditions, and has been successfully used in the substrates with acid-sensitive groups during our syntheses of Nakiterpiosion (11) and Nakiterpiosinone (12) ( Figure 1). [8] Furthermore, the hydrofluorenone motif frequently exists in bioactive-containing natural products, including abeo-abietane diterpenoids (taiwaniaquinoid B (13)), [9] Asterogynin A (14), [10] B (15), [10] and exiguaquinol (16). [11] Structurally related alkaloids, kanamycin A (17) [12] and gracilamine (18), [13] could also be easily derived from corresponding hydrofluorenone cores.…”

Catalytic Asymmetric Formal Total Synthesis of (−)-Triptophenolide and (+)-Triptolide

“…Hence, acceptable yield was obtained by adding p -TsOH at higher temperature. This provides a method to build cis backbone of 6-6-6 structure which is difficult to access by acidic cyclization [39]. However, after screening of different acids (Camphorsulfonic acid, TiCl 4 , BF 3 ·OEt 2 , Proline) and bases (KOH, K 2 CO 3 , KO- t -Bu), no further improvement was realized to produce more trans isomer.…”

Three New Abietane‐type Diterpenes from the Bark of Cryptomeria japonica

“…Compounds 1 – 5 are structurally and biogenetically related to the family of taiwaniaquinoids with an unusual 6‐5‐6‐abeoabietane skeleton, which were first isolated from the leaves of Taiwania cryptomerioides by Cheng . Some of them exhibited antitumor activities , and thus attracted remarkable attention from the synthetic researchers . Biosynthetically, the abietane‐6,7‐diol could undergo pinacol rearrangement to generate the uncommon 6‐5‐6 tricyclic skeleton of the taiwaniaquinoids with a trans ‐5,10‐bicyclic motif.…”