One‐Step Synthesis of Norabietane Core and its Alkylation to Abietane Analogs

Abstract

Synthesis of norabietane core.

Access to [6‐7‐6]‐Icetexanes through Sequential Cascade Cyclization and Biomimetic Ring Expansion

“…In the presence of a C1 carbonyl group in compound 4 , we explored the possibility of hydroxymethylation at the C10 position through kinetic enolate formation, followed by the addition of paraformaldehyde. Interestingly, this reaction resulted in an overreaction, yielding diol compound 5 , which had been observed in our previous study [20b] . Consecutively, diol compound 5 underwent primary alcohol triflation and subsequent a 1,2‐carbon rearrangement, leading to the formation of the ring‐expanded [6‐7‐6]‐icetexane product 6 (for a specific mechanism, refer to Scheme 6).…”

Intramolecular Cyclization of 2‐Alkynylphenylcarbonyls With a Pendant Double Bond under Copper Catalysis: A General Approach to Norabietane Core Structure

“…[15] First, we studied Cucatalyzed-cycloisomerization of 1 c to 2 c, which has been further functionalized at C-10 position by LDA promoted alkylation to afford 2 c derivatives possessing À Me, À CH 2 CH=CH 2 , À CH 2 Ph, and À CH 2 OH at C-10 position (Scheme 1). [16] Herein, we wish to report an efficient synthetic method involving metal-carbene species leading to [6,6,6] tricyclic compounds. Here we wish to report our recent advanced results covering previous results on enyne-als and enyne-ones under Cu-catalysis and their synthetic application to the prospective precursors leading to Lepenine natural alkaloid (Figure 3).…”

“…First, we studied Cu‐catalyzed‐cycloisomerization of 1 c to 2 c , which has been further functionalized at C‐10 position by LDA promoted alkylation to afford 2 c derivatives possessing −Me, −CH 2 CH=CH 2 , −CH 2 Ph, and −CH 2 OH at C‐10 position (Scheme 1). [16] …”

Various synthetic approaches for [6,7,m]‐tricyclic compounds containing an oxygen‐bridged skeleton

“…The cyclization precursor was obtained by Sonogashira coupling with the enyne and aromatic moieties. Cyclization was performed using conditions previously reported by our group 16 . Oxabicyclic compound 2a was formed by Rh‐catalyzed tandem cyclization–cycloaddition in 77% (Entry 1).…”