Collective Total Syntheses of Atisane‐Type Diterpenes and Atisine‐Type Diterpenoid Alkaloids: (±)‐Spiramilactone B, (±)‐Spiraminol, (±)‐Dihydroajaconine, and (±)‐Spiramines C and D

Abstract

The first total syntheses of the architecturally complex atisane-type diterpenes and biogenetically related atisine-type diterpenoid alkaloids (±)-spiramilactone B, (±)-spiraminol, (±)-dihydroajaconine, and (±)-spiramines C and D are reported. Highlights of the synthesis include a late-stage biomimetic transformation of spiramilactone B, a facile formal lactone migration from the pentacyclic skeleton of spiramilactone E, a highly efficient and diastereoselective 1,7-enyne cycloisomerization to construct the functionalized tetracyclic atisane skeleton, and a tandem retro-Diels-Alder/intramolecular Diels-Alder sequence to achieve the tricyclo[6.2.2.0] ring system.

Total Synthesis of Talatisamine

“…In order to employ aconvergent coupling process that can avoid stepwise carbon chain extensions,t his pentacycle was dissected into two structurally simple fragments having asimilar molecular size, chiral AE-ring 7 and aromatic D-ring 6.A zabicycle 7 was designed to possess the N-ethylpiperidine,C 1,C18-oxygen functionalities,a nd C4,C11-quaternary carbon centers of 1, and would be prepared from 2-cyclohexenone (8)inaconcise manner.O nt he other hand, the readily available aromatic ring 6 with the C14-oxygen functionality served as aprecursor of the saturated D-ring of 1.I nt he synthetic direction, coupling between 6 and 7,f ollowed by functional group manipulations including C10-olefination, would generate 5 having the requisite 19 carbons.Oxidative dearomatization of the D-ring of 5 and subsequent Diels-Alder reaction with the C10-olefin would lead to pentacycle 4a. [14,15] Then, the 6/6ring system of 4a would be reorganized into 7/5-membered BC-ring 3 via abiomimetic skeletal rearrangement, [16] thereby quickly building the ABCDE-ring skeleton. Thelast sequence from 3 to 2 would involve an adjustment of the C14,C16oxidation level and the olefin isomerization from C15 to C7.…”

A Unified Approach for the Assembly of Atisine‐ and Hetidine‐type Diterpenoid Alkaloids: Total Syntheses of Azitine and the Proposed Structure of Navirine C

“…Owing to their caged and polycyclic ring systems, the C 20 diterpenoid alkaloids (Figure ) are recognized among the most architecturally complex natural products, and have elicited considerable interest from the synthetic community over the past several decades . These synthetic campaigns culminated in the completion of formal and total syntheses of a subset of C 20 diterpenoid alkaloids, namely nominine ( 1 ), atisine ( 4 ), isoatisine ( 5 ), isoazitine ( 6 ), dihydroajaconine, gymnandine, spiramines C and D, and cochlearenine . However, most of these synthetic routes require a large number of steps and are restricted to a very particular structure .…”

Expedient Construction of the Hexacycle of Franchetine

“…Although the tetracyclic scaffolds imilart o12 has been previ-ously prepared by us using ac ycloisomerizationr eaction as the key ring closure strategy, [11] ar apid and steps economical approacht o12 would presented in this manuscript using a more efficient radical cyclization as the key transformation.…”

“…2018, 13,955 -958 www.chemasianj.org epoxide 19 in place,a ppropriate reactionc onditions for opening this epoxide with concomitant formation of ab ridged lactone on ring Bw ere investigated. The use of Lewis acids (BF 3 ·Et 2 O, [13] Ti(OiPr) 2 Cl 2 , [11] and ZnCl 2 [14] etc.) led to decomposition of the startingm aterialo rp rovided the halohydrins as the major product.…”