• Description and Characteristics of the Main Reagents
• Cleavage of the Carbon-Heteroatom Single Bond
• Reduction of Double Bonds
• Reduction of Triple Bonds
• Other Derivatives
• Synoptic Tables
• References
• Index

• Successful techniques for performing highly selective reductions
• Chemo-, regio-, stereo-, and enantioselective reductions of both simple and complex compounds
• Best methods for obtaining the main functional groups by hydridereduction, provided in quick-reference tabular form
• New and more selective reagents developed within the last five years
• Experimental conditions, including solvent and temperature, and yields for most cases described.

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Review: Reductions by the Alumino- and Borohydrides in Organic Synthesis, 2nd edition (by Jacqueline Seyden-Penne)
Hoye, R. C. J. Chem. Educ. 76, 33 (1999)

This book focuses entirely on the aluminohydride and borohydride reducing agents. It condenses a large body of information into a valuable user-friendly resource for synthetic organic chemists. The author states that "This second edition has been broadly updated, but it is no longer exhaustive. As in the previous edition, the examples are selected in order to cover problems that are frequently encountered in synthesis."

The first chapter (13 pages) gives an excellent summary of the approximately two dozen most widely used aluminohydride and borohydride reagents. Information is presented on the main applications of each reagent and its solubility characteristics, stability, and handling requirements. Cross-references are liberally given to subsequent chapters where more complete reactivity profiles and examples are found. Chapters two through five (155 pages) detail reduction of the main functional groups by these reagents.

Chapter two covers reductions of carbon-heteroatom single bonds (C-Hal, C-O, C-N, C-P). Reagents capable of effecting a desired single-bond cleavage are described, as are mechanistic considerations of the process. Chemoselectivity and regioselectivity are duly noted.

Chapter three is concerned with reduction of double bonds (C=C, C=O, C=N) and is by far the largest chapter in the book. Reduction of carbon-oxygen double bonds is organized by functional group. The examples for aldehydes and ketones illustrate the potential for selectivity in the presence of other functional groups; the control of stereoselectivity, including a discussion of the factors favoring the Felkin-Ahn or Houk models; a survey of enantioselective reducing agents, particularly those developed in recent years; and the influence of neighboring substituents on stereoselectivity as the result of chelation control. These concerns and further consideration of conditions for partial reduction are given for carboxylic acid derivatives. Similar examples are included for reduction of carbon-nitrogen double bonds.

Carbon-carbon and carbon-nitrogen triple bonds, both isolated and conjugated, are treated in Chapter four. The examples illustrate the potential for chemo-, regio-, and stereoselectivity. Chapter five addresses the reduction of "other derivatives", including nitro and nitroso derivatives, azides, organometallics, sulfides (sulfoxides, sulfones, and amine oxides), phosphine oxides and phosphates, silyl derivatives, and boron reagents. Seyden-Penne concludes with a large table (11 pages) that "shows at a glance" the various methods by which major functional groups can be obtained by hydride reduction with cross references to the appropriate sections of the text.

This book is a thorough and dense compilation of experimental results and observations that highlight selectivity at every level as well as experimental practicality. The 10-page index appears to be well organized and the referencing is extensive (more than 1000 references in 33 pages). Given the prevalent role of hydride reduction reactions in organic synthesis, many practitioners will want to have ready access to this book, and it is a must for all science libraries.

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Review: Reductions by the Alumino- and Borohydrides in Organic Synthesis (by J. Seyden-Penne)
K. Smith, Appl. Organometal. Chem. 12, 881 (1998)

This book is an update from the first edition, which was published in 1991. In the first edition there was an attempt at comprehensive coverage of the topic, but in the second edition any such attempt has been forced to be abandoned. Nevertheless, this second edition is packed with information, cites around 1200 references, and provides a very useful source for anyone contemplating a complex hydride reduction.

The book is organized into five chapters, followed by 11 pages of synoptic tables, then the references and a subject index.

Chapter 1 introduces the most commonly used reagents, indicates their stability and solubility characteristics and briefly describes their main applications. Chapters 2–5 present the reduction of the main functional groups, with reference to features of selectivity and compatibility.
Chapter 2 deals with cleavage of carbon–heteroatom single bonds (halides, sulphonates, epoxides, alcohols, ethers, ammonium salts etc).
Chapter 3, the largest chapter with over 100 pages, deals with reduction of double bonds (other than C=C bonds). The bulk of the chapter (85 pages) concerns reductions of carbonyl compounds, including sections on different kinds of carbonyl compounds, asymmetric reductions and regioselectivity of the reduction of a,b-unsaturated derivatives. The chapter also covers imines, enamines, nitrogen heterocycles and oximes/hydrazones.
Chapter 4 deals with reduction of triple bonds and Chapter 5 with other derivatives (nitro compounds, azides, organometallics, and sulphur, phosphorus, silicon and boron compounds).

The entry point for many will be the synoptic tables. Here it is possible to look up a class of compound and choose a precursor substrate; the table will provide a list of reagents for the transformation and section references indicating where the reactions are discussed. The appropriate sections in Chapters 2–5 will provide the detailed discussion of those reactions and Chapter 1 will give an outline of the characteristics of the chosen reagent. Thus, the book is ideal for identifying the most useful references for any given reduction.

Because it is so densely packed with information, the text is somewhat difficult to read. This is almost unavoidable if the coverage is to remain so full and the book so short (220 pages), and the difficulty is easily outweighed by the value of the work as a source of reference and information.

This book is an imperative purchase for all chemical libraries and for any individuals who make regular use of complex hydride reductions.

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