Regioselectivity of the Reactions of Heteroatom-Stabilized Allyl ...

Alan Katritzky is Kenan Professor and Director of the Center for
Heterocyclic Chemistry at the University of Florida, where his large
research group is investigating how structure determines chemical and
physical properties, using both experimental and theoretical approaches,
and developing of synthetic methodology. He holds honorary doctorates
from universities in Spain, Poland, France, U.K., Russia, and Romania,
medals from Belgium, Czech Republic Estonia, Greece, Italy, and U.K.,
foreign memberships of the Polish and Catalan Academies, a F.R.S.,
honorary memberships of the Polish and Italian Chemical Societies, and
honorary Professorships from China.
Michaela Piffl was born in 1971. After having studied at Friedrich-Schiller-
University Jena, Germany, the University of Strathclyde Glasgow, U.K.,
and King’s College London, U.K., she received her Diploma in 1995 in
Jena. She investigated heterogeneous catalysts for the dimerization of
acrylonitrile. Her work was supported by the Studienstiftung des Deutschen
Volkes. Currently, she is in the third year of her Ph.D. with Professor
Anders. Her research interest is regioselective electrophilic attack at
heterosubstituted allyl anions.
I. Introduction, Synthetic Importance, and
Theoretical Significance
Allyl anions are stabilized by resonance, and are
considerably more stable than alkane anions: allyllithium
has a stabilization energy of -15.7 kcal/mol,
whereas that for n-propyllithium has been calculated
to be 4.0 kcal/mol. 1 Furthermore, propene has a pKa
of 47.1-48.0 2a (or ) 43 2b ), whereas the pKa of alkanes
are between 50 and 60. 3 Considerable further stabilization
can arise when an allylic anion contains a
heterosubstituent. An unsymmetrically substituted
allyl anion 2 is an ambident anion, which can react
with electrophiles at two sites (cf. Scheme 1). The site
selectivity of such reactions is both of considerable
synthetic importance and of theoretical interest, and
the discussion of such site selectivity to give 1 vs 3
is a major objective of this review.
Hengyuan Lang was born in China in 1962. He received his Ph.D. from
Beijing Institute of Technology in 1989. Following five years of postdoctoral
studies in Professor Katritzky’s group at the University of Florida, he is
now a research scientist at Trega Biosciences, Inc., San Diego, working
on the design and synthesis of small molecular and heterocyclic
combinatorial libraries. He has authored or co-authored more than 40
scientific papers and patents.
Professor Ernst Anders was born in 1942 in Germany. He studied
chemistry at the Free University of Berlin and received his Ph.D. in
theoretical and organic chemistry working with Professor Ernst Ruch at
the Institute of Quantum Chemistry. He then moved to the Friedrich-
Alexander-University of Erlangen-Nürnberg (Bavaria) to work on heterocyclic
chemistry with Professor Hans-Jürgen Bestmann. After receiving
his Doctor habilitus and the position of a Professor of Organic Chemistry
at the University of Erlangen-Nürnberg, he was Visiting Professor in
Göttingen, Germany, and Gainesville, FL. In 1993 he took his present
position as a Full Professor at the Institute of Organic Chemistry and
Macromolecular Chemistry (IOMC, Friedrich-Schiller-University of Jena).
From 1995 to 1997, he was the Director of the IOMC. Presently he is the
Vice Dean of the Faculty of Chemistry and Earth Sciences and chairman
of the Collaborative Research Center (SFB No. 436) “Synthetic Analogues
of Naturally Occurring Metal-Assisted Reactions”. His present research
fields focus on stereoelectronically stabilized cations, heterocyclic chemistry,
organo−metal complexes, and computational chemistry.
An important role of heterosubstituted allyl anions
is in the umpolung of carbonyl groups. The carbonyl
function plays a central role in organic synthesis,
consequently numerous transformations of this group
have been developed. The carbonyl carbon usually
serves as the electrophilic partner in polar condensation
processes. However, a great deal of effort has
Scheme 1
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