Summary—The Reactions of Organometallic Reagents

We have now seen many different reactions of organometallic reagents with a variety of functional groups, and you may have some difficulty keeping them all straight. Rather than memorizing them all, keep in mind the following three concepts  

The reactions learned in Chapter 20 have proven extremely useful in organic synthesis. Oxidation and reduction reactions interconvert two functional groups that differ in oxidation state. Organometallic reagents form new carbon-carbon bonds. 

Synthesis is perhaps the most difficult aspect of organic chemistry. It requires you to remember both the new reactions you ve just learned, and the ones you ve encountered in previous chapters. In a successful synthesis, you must also put these reactions in a logical order. Don t be discouraged. Learn the basic reactions and then practice them over and over again with synthesis problems. 

Before proceeding with Sample Problems 20.6—20.8, you should review the stepwise strategy for designing a synthesis found in Section 11.12. 

Chapter 20 Introduction to Carbonyl Chemistry Organometallic Reagents Oxidation and Reduction 

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The purpose of this review is to provide a summary (through to the end of 1988) of the uncatalyzed reactions of type I and type III allyl organometallics with C X electrophiles. Most of the examples involve aldehydes and ketones, but the reactions of allyl organometallics with imines are also covered. Because the focus of this review is on selectivity and synthetic efficiency, this review is not intended to be as comprehensive as an Organic Reactions chapter or a Chemical Reviews article. Rather, we have attempted to define and illustrate the factors that influence stereoselectivity, to provide access to the most pertinent literature, and, most importantly, to provide a basis for selection of an allyl organometallic reagent for application in specific synthetic problems. 

In summary, sulfonamides are most commonly prepared by the reaction of amines with sulfonyl halides. Aryl sulfonyl chlorides may be accessed from C-H bonds by chlorosulfonylation, from C-S bonds by oxidation, from C-N bonds by diazotization, or from C-X bonds by metalation. Approaches to all l sulfonamides are more limited as they are typically prepared by either oxidative chlorination of thiols or addition of organometallic nucleophiles to sulfur electrophiles. Traditional sulfonamide preparation has frequently necessitated harsh reagents and conditions, but the development of Pd-catalysed approaches and discovery of new sulfur dioxide sources allow for operationally simple sulfonamide synthesis under mild conditions. Future directions in sulfonamide synthesis will likely involve the direct C-H installation of sulfonamides without the use of hazardous reagents. 

Since Kosolapoff s classic summary of the chemistry of organophosphorus compounds (116), many advances in the techniques required for study of these materials have been developed. Selective displacement of halide ions and/or alkoxy (or aryloxy) groups from a phosphorus atom by organometallic reagents is a convenient process of synthetic importance for an enormous variety of organophosphorus compounds. Only within the past few years has data been made available on the mechanism of this type of reaction, but further study is necessary for a complete interpretation. We have attempted to correlate the existing information with emphasis on synthetic utility and application to the manner of displacement of halide ion and OR groups attached to phosphorus. Selection of examples for discussion is arbitrary, of course, but an attempt was made to include topics for which... 

Chemical reagents can also be used to carry out redox intercalation reactions. Alkali metals in liquid ammonia and organometallic reagents such as n-butyllithium were among the earliest used. Other chemical reagents can be used to provide different effective activities of the alkali metal relative to the pure metal. A convenient summary, developed for comparison of the reduction potentials for some common lithium reagents and common host lattices, is shown in Figure 5. ... 

Reactions of Allyl and Vinyl Anions. A brief summary of some key reactions reported in this area is recorded here. This area is also partly covered in Chapter 8. The results are summarized in Table 11. A comparison of the reactivity of ene-sulphides and ene-ethers towards organometallic reagents revealed remarkable differences. With thio compounds metallation at the olefinic site next to the heteroatom dominates clearly over the alternative deprotonation of an allylic position. Only with propenyl phenyl sulphide were both exchange modes observed simultaneously, whereas in all higher homologues as well as vinyl phenyl sulphide the metal was exclusively attached to the olefinic a-carbon atom. ... 

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