Chemistry Reference
In-Depth Information
10
ASYMMETRIC CARBONYLATIONS
CYRIL GODARD , AURORA RUIZ , MONTSERRAT DI É GUEZ ,
OSCAR P À MIES , AND CARMEN CLAVER
Department of Physical Chemistry and Inorganic Chemistry, Universitat Rovira i Virgili,
Campus Sescelades, C/Marcel.li Domingo s/n 43007, Tarragona, Spain
10.1. INTRODUCTION
Transition metal-catalyzed carbonylation is one of the most straightforward tools to
obtain fi ne chemicals intermediates from alkenes and other unsaturated products.
Together with asymmetric hydrogenation, asymmetric C-C bond formation, and asym-
metric allylic substitutions, the asymmetric carbonylations are among the most challeng-
ing homogeneous processes. Their potential is still to be made the most of, perhaps
because of the complexity of these reactions where aldehydes, esters, or acids can be
formed from simple olefi ns and enantiomerically pure products or enantiomeric enrich-
ment of one of the products can be obtained when the transition metal catalyst is modi-
fi ed with a chiral ligand. The most famous asymmetric carbonylation process is the
Rh-catalyzed hydroformylation of alkenes, together with the Pd-catalyzed hydroxy- or
alkoxycarbonylation of alkenes. There are, however, important differences between
these processes, as the rhodium-catalyzed hydroformylation is of greater industrial inter-
est than the palladium carbonylations. From the mechanistic point of view, rhodium-
catalyzed hydroformylation has been much more studied and understood than the
palladium-catalyzed carbonylations maybe because of the stability of rhodium species,
as well as the applicability of spectroscopic high-pressure (HP) nuclear magnetic reso-
nance (NMR) techniques for the study of the intermediates and the early application of
rhodium hydroformylation in industry as “oxo” process. As a result, the last develop-
ments in rhodium-catalyzed hydroformylation led to a very good control of the regiose-
lectivity to the desired product as well as the preparation of practically enantiomerically
pure aldehydes. Palladium-catalyzed carbonylations, both alkoxycarbonylation and
hydroxycarbonylation, have also been widely studied but present more issues to obtain
