A Rapid Stereocontrolled Entry to the ABCD Tetracyclic Core of Neotuberostemonine

Abstract

Four out of the five rings of the alkaloid neotuberostemonine (1) are present in the advanced precursor 2. The tetracyclic compound 2 has now been prepared in a short, linear route via lactone acid 3. A key step in the synthesis was the cuprate‐mediated SN2′ ring‐opening desymmetrization of the C2‐symmetric bislactone 4.

Photochemical Reactions as Key Steps in Organic Synthesis

“…The rearrangement leads to the tricycle 40 in high yields. This motif is found as a core structure in various alkaloids such as neotuberostemonine, stenine, and tuberostemonine (Figure ) . The reaction also provides a versatile approach to bi- or tricyclic derivatives of perhydroazaazulene .…”

Rapid Access to Azepine-Fused Oxetanols from Alkoxy-Substituted Maleimides

“…Previously, we reported that N -pentenyl-substituted maleimide derivatives 1 undergo an efficient formal [5 + 2] cycloaddition reaction on UV irradiation . The reaction has proved to be general for a range of maleimide derivatives and has recently been used by us as a key step in alkaloid synthesis . The reaction is related to similar photochemistry described by Mazzocchi 3 for phthalimide derivatives and is thought to proceed by initial [2 + 2] cycloaddition to form the zwitterion 2 , which then undergoes fragmentation to the azepine 3 (Scheme ).…”

A Protecting Group Free Synthesis of (±)-Neostenine via the [5 + 2] Photocycloaddition of Maleimides

“…This group has very recently been able to modify their approach to deliver the first total synthesis of (±)-neostenine 5 . In 2001, we embarked on a program to deliver neotuberostemonine 6 by a strategy that was to proceed via the use of an oxo derivative of neostenine 5 as an advanced intermediate . At the time, 5 had not been identified, but following its isolation in 2003 it was evident that it would be within reach of our ongoing route to 6 .…”