Synthesis and Rearrangement Control of Substituted Benzobicycloheptane Aziridines

Abstract

A general synthesis of various substituted benzonorbornene derivatives is described. Benzenesulfonyl aziridines of these compounds were prepared and their acetolysis was studied. The influence of various substitution patterns on the direction of the aziridine rearrangement is discussed and it is shown that the rearrangements may be used as a convenient approach to the synthesis of ring B bridged diterpene alkaloids. Considerable general synthetic utility of these techniques is anticipated.

The synthesis of chasmanine: aromatic intermediate

“…The conversion of the ester 4 via the intermediates 5 and 6 to the tricyclic ester 7 was described previously (4). This process has now been improved and is recorded in the Experimental.…”

“…The starting materials for the present synthesis were the compounds 7 and 16 both of which we have previously reported (4,5). However, both these compounds were now prepared by fundamentally improved methods.…”

“…It was converted into the methyl ester 4 by esterification with gaseous hydrochloric acid in methanol. We have previously prepared compounds 3 and 4 by a less efficient method (4) and the identity of our present materials with the reference samples was established by mixture melting points and spectral d a t a 2…”

“…This was corrected by the introduction of the bridgehead methoxyl, which helped to steer the rearrangement in the desired direction. A detailed discussion of the various factors influencing the direction of aziridine rearrangements may be found in the first paper of this series (4).…”

Total Syntheses of the C19 Diterpenoid Alkaloids (−)-Talatisamine, (−)-Liljestrandisine, and (−)-Liljestrandinine by a Fragment Coupling Approach

“…Biosynthetically, the C19 DTAs arise via the ent -atisane cyclase pathway, in which the originally formed denudatine framework ( 4 ), containing a bicyclo[2.2.2]­octane CD ring system, undergoes skeletal rearrangement to the corresponding [3.2.1] CD ring system ( 5 ) (Figure b) . The cationic rearrangements involved in the biosynthesis of these natural products have also played an important role in many of the total syntheses of the C19 DTAs, including the pioneering efforts in the 1970s by Wiesner and co-workers, − and more recent contributions by the Sarpong, Fukuyama, and Inoue laboratories . In each of these approaches, the denudatine-type bicyclo[2.2.2]­octane is first assembled by a Diels–Alder reaction, and then rearranged at a late stage to the aconitine-type skeleton.…”