Vol.:(0123456789)
Topics in Current Chemistry (2020) 378:1
https://doi.org/10.1007/s41061-019-0261-4
1 3
REVIEW
Asymmetric Reactions Enabled by Cooperative
Enantioselective Amino‑ and Lewis Acid Catalysis
Pier Giorgio Cozzi, et al. [full author details at the end of the article]
Received: 18 May 2019 / Accepted: 22 October 2019 / Published online: 25 November 2019
© Springer Nature Switzerland AG 2019
Abstract
Organocatalysis—the branch of catalysis featuring small organic molecules as the
catalysts—has, in the last decade, become of central importance in the field of
asymmetric catalysis, so much that it is now comparable to metal catalysis and biocatalysis. Organocatalysis is rationalized and classified by a number of so-called
activation modes, based on the formation of a covalent or not-covalent intermediate
between the organocatalyst and the organic substrate. Among all the organocatalytic
activation modes, enamine and iminium catalysis are widely used for the practical
preparation of valuable products and intermediates, both in academic and industrial
contexts. In both cases, chiral amines are employed as catalysts. Enamine activation
mode is generally employed in the reaction with electrophiles, while nucleophiles
require the iminium activation mode. Commonly, in both modes, the reaction occurs
through well-organized transitions states. A large variety of partners can react with
enamines and iminium ions, due to their sufficient nucleophilicity and electrophilicity, respectively. However, despite the success, organocatalysis still suffers from
narrow scopes and applications. Multicatalysis is a possible solution for these drawbacks because the two different catalysts can synergistically activate the substrates,
with a simultaneous activation of the two different reaction partners. In particular, in
this review we will summarize the reported processes featuring Lewis acid catalysis and organocatalytic activation modes synergically acting and not interfering with
each other. We will focus our attention on the description of processes in which good
results cannot be achieved independently by organocatalysis or Lewis acid catalysis.
In these examples of cooperative dual catalysis, a number of new organic transformations have been developed. The review will focus on the possible strategies, the
choice of the Lewis acid and the catalytic cycles involved in the effective reported
combination. Additionally, some important key points regarding the rationale for
the effective combinations will be also included. π-Activation of organic substrates
by Lewis acids, via formation of electrophilic intermediates, and their reaction with
enamines will be also discussed in this review.
Reprinted from the journal
29
Chapter 2 was originally published as Cozzi, P. G., Gualandi, A., Potenti, S., Calogero, F. & Rodeghiero, G.
Topics in Current Chemistry (2020) 378: 1. https://doi.org/10.1007/s41061-019-0261-4.
Topics in Current Chemistry (2020) 378:1
https://doi.org/10.1007/s41061-019-0261-4
1 3
REVIEW
Asymmetric Reactions Enabled by Cooperative
Enantioselective Amino‑ and Lewis Acid Catalysis
Pier Giorgio Cozzi, et al. [full author details at the end of the article]
Received: 18 May 2019 / Accepted: 22 October 2019 / Published online: 25 November 2019
© Springer Nature Switzerland AG 2019
Abstract
Organocatalysis—the branch of catalysis featuring small organic molecules as the
catalysts—has, in the last decade, become of central importance in the field of
asymmetric catalysis, so much that it is now comparable to metal catalysis and biocatalysis. Organocatalysis is rationalized and classified by a number of so-called
activation modes, based on the formation of a covalent or not-covalent intermediate
between the organocatalyst and the organic substrate. Among all the organocatalytic
activation modes, enamine and iminium catalysis are widely used for the practical
preparation of valuable products and intermediates, both in academic and industrial
contexts. In both cases, chiral amines are employed as catalysts. Enamine activation
mode is generally employed in the reaction with electrophiles, while nucleophiles
require the iminium activation mode. Commonly, in both modes, the reaction occurs
through well-organized transitions states. A large variety of partners can react with
enamines and iminium ions, due to their sufficient nucleophilicity and electrophilicity, respectively. However, despite the success, organocatalysis still suffers from
narrow scopes and applications. Multicatalysis is a possible solution for these drawbacks because the two different catalysts can synergistically activate the substrates,
with a simultaneous activation of the two different reaction partners. In particular, in
this review we will summarize the reported processes featuring Lewis acid catalysis and organocatalytic activation modes synergically acting and not interfering with
each other. We will focus our attention on the description of processes in which good
results cannot be achieved independently by organocatalysis or Lewis acid catalysis.
In these examples of cooperative dual catalysis, a number of new organic transformations have been developed. The review will focus on the possible strategies, the
choice of the Lewis acid and the catalytic cycles involved in the effective reported
combination. Additionally, some important key points regarding the rationale for
the effective combinations will be also included. π-Activation of organic substrates
by Lewis acids, via formation of electrophilic intermediates, and their reaction with
enamines will be also discussed in this review.
Reprinted from the journal
29
Chapter 2 was originally published as Cozzi, P. G., Gualandi, A., Potenti, S., Calogero, F. & Rodeghiero, G.
Topics in Current Chemistry (2020) 378: 1. https://doi.org/10.1007/s41061-019-0261-4.