A hidden catalysis: metal-, and organocatalyst-free one-pot assembly of chiral aza-tricyclic molecules

25 May 2021, Version 3
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Development of a rapid synthesis of complex molecules from simple building blocks under a metal-and organocatalyst-free condition is both conceptually and chemically challenging. Here, we developed a hidden catalysis that allow the straightforward assembly of enantiopure aza-tricyclic molecules containing six contiguous stereocenters from aminophenols, α,β-unsaturated aldehydes and α-amino acids. Without using a metal or an organocatalyst, our approach relies on a temporary formation of a spiroimidazolidinone intermediate and its participation in a sequential aza-Michael/Michael reaction as both a substrate and a catalyst under an iminium/enamine catalysis. The formation of the putative iminium intermediate was supported by spectroscopic data and its interruptive reduction derivative was isolated and fully characterized. Whereas a conventional catalyst is always present and does not undergo a permanent chemical change in a classic catalysis, the spiroimidazolidinone intermediate is conceptualized as a sub-catalyst as it is only temporary produced from precursors and catalyzes its own consumption. This unique substrate-catalyst (sub-catalyst) dual role of the spiroimidazolidinone induces a substantial steric discrimination in the transition state and an excellent overall diastereoselectivity (>20:1 dr). It allows the use of an amino acid precursor as the sole chirality genesis and avoids the use of transition metals or organocatalysts. An enantiomer of an aza-tricyclic imidazolidinone can be prepared from a commercially available amino acid precursor. The aqueous-based reaction is practical and scalable for multi-gram synthesis. The success of implementing this sub-catalysis concept in the synthesis will pave the way for many efficient chiral catalyst-free preparations of chiral complex molecules.


Keywords

Sub-catalysis, hidden Catalyst, one-pot reaction, spiroimidazolidinone

Supplementary materials

Title
Description
Actions
Title
Supporting information
Description
Actions

Comments

Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.