Rh-Catalyzed Cycloaddition Cascade of Allenynes and Maleimides: A Powerful Strategy for Constructing Complex Pentacyclic Structures with a Bicyclo[2.2.2]octene Core

TL;DR

This paper introduces a new chemical reaction that efficiently builds complex five-ring structures using allenynes and maleimides.

Contribution

The study reveals a novel cascade mechanism involving a noncanonical [2+2+2] cycloaddition and a thermal Diels–Alder reaction.

Findings

1,5- and 1,6-allenynes react with maleimides to form pentacyclic structures with a bicyclo[2.2.2]octene core.

DFT calculations and deuterium-labeling studies support an unconventional reaction pathway.

The cascade includes a diastereoselective process and a thermal Diels–Alder reaction with a second maleimide.

Abstract

Herein, we report that 1,5- and 1,6-allenynes react with
two equivalents
of maleimide to afford pentacyclic frameworks featuring a bicyclo[2.2.2]­octene
core in a fully diastereoselective fashion. DFT calculations and deuterium-labeling
studies reveal an unconventional mechanism initiated by a noncanonical
[2 + 2 + 2] cycloaddition that, through intramolecular hydrogen shifts,
diverges from the classical pathway to generate a conjugated diene.
A subsequent thermal Diels–Alder reaction with a second maleimide
completes the cascade, unveiling a distinct reactivity mode.

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