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16
Enantioselective Addition Reactions Catalyzed by
Carbohydrate-Derived Organocatalysts
Jun-An Ma and Guang-Wu Zhang
16.1
Introduction
Enantioselective organocatalysis is regarded as a complementary protocol to the
long-established metal-complex and enzyme-catalyzed procedures. A century ago,
Bredig and Fiske reported the use of natural alkaloids to catalyze the synthesis
of cyanohydrins [1]. About 60 years later, two industrial groups independently
reported the now well-known intramolecular aldol reaction catalyzed by l-proline
[2]. Even though after this pioneering work there were several reports on small
organic molecules promoting synthetic transformations without any assistance by
metal compounds [3], for many years organocatalysis received very little attention.
Only since the beginning of the new century are we witnessing a remarkable
renewal of interest in enantioselective organocatalysis [4].
In this upcoming area of chemistry, a lot of synthetic tools are based on well-
known compounds of the
chiral pool,
such as amino acids, alkaloids, and tartaric
acid. Carbohydrates, which are inexpensive and readily available natural materials,
have only recently also been employed as chiral backbones of organocatalysts [5]. For
example, in the 1990s Shi and coworkers successfully applied the fructose-derived
ketones as chiral organocatalysts in asymmetric epoxidation reactions of olefins [6]
(cf. also Chapter 15); and Roberts' group described carbohydrate-derived thiols as
chiral organocatalysts for the enantioselective radical additions (see below). In the
following sections, the focus will be on several enantioselective addition reactions
to C=N, C=C, and C=O bonds, mediated by carbohydrate-derived organocatalysts.
16.2
Strecker, Mannich, and Nitro-Mannich Reactions
1,2-Additions of carbon nucleophiles to C=N bonds such as Strecker [7] and
Mannich [8] reactions are very important and fundamental C-C bond-forming
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