REARRANGEMENTS IN NATURAL PRODUCT SYNTHESIS - Modern Tools for the Synthesis of Complex Bioactive Molecules - page 241

8
REARRANGEMENTS IN NATURAL
PRODUCT SYNTHESIS

CHAPTER

JOS ´ MARCO-CONTELLES and ELENA SORIANO
Laboratorio de Qu ımicaMedica y Computacional, Instituto de Qu ımica Organica General,
Madrid, Spain

8.1. INTRODUCTION

Molecular rearrangements occupy center stage in the development of organic
synthesis [1] and have resulted in various impressive achievements that have been
reported in the last decades [2]. Accordingly, the purpose of this chapter is to highlight
the use of a set of selected molecular rearrangements and show how these reactions
have been utilized as efficient regio-, enantio-, and chemoselective synthetic tools for
the preparation of complex bioactives.
Our selection has been mainly addressed to pericyclic reactions, among them
the [3,3]-sigmatropic rearrangements [3], which continue to provide excellent
opportunities for reaching high chemical diversity. In the class of the [3,3]-
sigmatropic rearrangements, focus will be on the neutral [3,3]-sigmatropic Cope [4],
oxy-Cope/anionic oxy-Cope [5], Claisen [4], and Overman [6] rearrangements, as
well as the cationic [3,3]-sigmatropic Petasis-Ferrier [7] and Prins-pinacol [8]
rearrangements, and the anionic [1,2]- and [2,3]-sigmatropic Wittig rearrange-
ments [9]. Finally, and in order to complement the selected pericyclic reactions, we
will end this chapter with some very well-known propargylic rearrangements, such as
the Meyer-Schuster and Rupe rearrangements [10], which are very useful synthetic
methods for the transformation of allylic alcohols into a , b -unsaturated carbonyl
derivatives. It is worth pointing out that these rearrangements are among the most
basic and useful transformations in synthetic organic chemistry. This is due to the fact
that these rearrangements are efficient for controlling quaternary, sterically hindered
chiral centers and for building carbon-carbon and carbon-heteroatom bonds in a
stereoselective fashion. In addition, [3,3]-sigmatropic rearrangements can be easily
integrated and adapted in cascade processes as simple methods to prepare complex
molecules in atom-economical reactions.