Page 6 - Advanced Organic Chemistry Part B - Reactions & Synthesis

vi Chapters 7 to 9 deal with organometallic reagents and catalysts. Chapter 7
considers Grignard and organolithium reagents. The discussion of organozinc reagents
Preface
emphasizes their potential for enantioselective addition to aldehydes. Chapter 8
discusses reactions involving transition metals, with emphasis on copper- and
palladium-mediated reactions. Chapter 9 considers the use of boranes, silanes, and
stannanes in carbon-carbon bond formation. These three chapters focus on reactions
such as nucleophilic addition to carbonyl groups, the Heck reaction, palladium-
catalyzed cross-coupling, olefin metathesis, and allyl- boration, silation, and stanny-
lation. These organometallic reactions currently are among the more important for
construction of complex carbon structures.
Chapter 10 considers the role of reactive intermediates—carbocations, carbenes,
and radicals—in synthesis. The carbocation reactions covered include the carbonyl-ene
reaction, polyolefin cyclization, and carbocation rearrangements. In the carbene section,
addition (cyclopropanation) and insertion reactions are emphasized. Catalysts that
provide both selectivity and enantioselectivity are discussed. The section on radicals
considers both intermolecular and intramolecular (cyclization) addition reactions of
radicals are dealt with. The use of atom transfer steps and tandem sequences in
synthesis is also illustrated.
Chapter 11 focuses on aromatic substitution, including electrophilic aromatic
substitution, reactions of diazonium ions, and palladium-catalyzed nucleophilic
aromatic substitution. Chapter 12 discusses oxidation reactions and is organized on
the basis of functional group transformations. Oxidants are subdivided as transition
metals, oxygen and peroxides, and other oxidants.
Chapter 13 illustrates applications of synthetic methodology by multistep synthesis
and perhaps provides some sense of the evolution of synthetic capabilities. Several
syntheses of two relatively simple molecules, juvabione and longifolene, illustrate
some classic methods for ring formation and functional group transformations and,
in the case of longifolene, also illustrate the potential for identification of relatively
simple starting materials by retrosynthetic analysis. The syntheses of Prelog-Djerassi
lactone highlight the methods for control of multiple stereocenters, and those of the
Taxol precursor Baccatin III show how synthesis of that densely functionalized tricyclic
structure has been accomplished. The synthesis of epothilone A illustrates both control
of acyclic stereochemistry and macrocyclization methods, including olefin metathesis.
The syntheses of + -discodermolide have been added, illustrating several methods
for acyclic stereoselectivity and demonstrating the virtues of convergency. The chapter
ends with a discussion of solid phase synthesis and its application to syntheses of
polypeptides and oligonucleotides, as well as in combinatorial synthesis.
There is increased emphasis throughout Part B on the representation of transition
structures to clarify stereoselectivity, including representation by computational
models. The current practice of organic synthesis requires a thorough knowledge of
molecular architecture and an understanding of how the components of a structure
can be assembled. Structures of enantioselective reagents and catalysts are provided
to help students appreciate the three-dimensional aspects of the interactions that occur
in reactions.
A new feature of this edition is a brief section of commentary on the reactions
in most of the schemes, which may point out a specific methodology or application.
Instructors who want to emphasize the broad aspects of reactions, as opposed to
specific examples, may wish to advise students to concentrate on the main flow of the
text, reserving the schemes and commentary for future reference. As mentioned in the