Chemistry Reference
In-Depth Information
2A
ENANTIOSELECTIVE
ORGANOCATALYSIS INVOLVING
IMINIUM, ENAMINE, SOMO, AND
PHOTOREDOX ACTIVATION
ALLAN J. B. WATSON AND DAVID W. C. MACMILLAN
Department of Chemistry, Frick Laboratory, Princeton University, Princeton, NJ
2A.1. INTRODUCTION
Enantioselective organocatalysis has become a fi eld of central importance within asym-
metric chemical synthesis. Within this fi eld, the concept of using chiral amines to effect
asymmetric bond formations has resulted in two extraordinarily powerful, and comple-
mentary, generic activation platforms. Over the last 10 years, iminium and enamine
catalysis have grown from a handful of unique reactions to over 70 widely applicable
enantioselective transformations, enabling unprecedented access to a host of chiral
molecules. This chapter aims to introduce the concepts of iminium and enamine catalysis
and to survey some of the most important achievements in each of these areas. In addi-
tion, recent extensions of these technologies are discussed.
2A.2. IMINIUM - BASED CATALYSIS
[1,2]
The fi rst organocatalytic generic activation mode to be truly designed, iminium catalysis
was introduced as a general strategy for asymmetric synthesis based on the capacity of
chiral amines to function as enantioselective catalysts for a range of transformations that
traditionally employ Lewis acids. This catalysis concept was founded on the mechanistic
hypothesis that the reversible formation of iminium ions, from
- unsaturated carbonyl
compounds and chiral secondary amines, might emulate the equilibrium dynamics and
α
,
β
