Hydride Reductions and 1,2-Additions of Nucleophiles to Carbonyl Compounds Using Carbohydrate-Based Reagents and Additives - Carbohydrates: Tools for Stereoselective Synthesis - page 123

6
Hydride Reductions and 1,2-Additions of Nucleophiles to
Carbonyl Compounds Using Carbohydrate-Based Reagents
and Additives
Omar Boutureira and Benjamin G. Davis
6.1
Introduction
The enantioselective addition of organometallic reagents to carbonyl compounds
is one of the most important processes in organic synthesis. In particular, the use
of carbohydrates as a source of chirality to control the outcome of such transforma-
tions has emerged as a versatile and powerful synthetic tool for the preparation of
enantiomerically pure compounds. Carbohydrates are a naturally occurring, inex-
pensive, renewable, readily available source of chirality that contain a high density
of stereogenic centers and may provide advantageously functional groups that can
in principle be systematically modified for altered enantiomeric differentiation.
The present chapter will deal with the application of carbohydrates, in particular
as chiral reagents and additives that have already proven to be effective chiral
inducers in asymmetric hydride reductions and 1,2-additions of nucleophiles to
carbonyl compounds [1-8].
6.2
Hydride Reductions
The enantioselective reduction of carbonyl compounds continues to attract the
attention of organic chemists. Since enantiomerically pure secondary alcohols
are often important building blocks for the preparation of biologically active
products, numerous carbohydrate-based asymmetric reducing agents have been
reported [9-12]. These reagents are mainly chirally modified aluminum and boron
hydrides.