Introduction to Alkyne Reactions

All reactions of alkynes occur because they contain easily broken ft bonds or, in the case of terminal alkynes, an acidic, sp hybridized C—H bond. 

Like alkenes, alkynes undergo addition reactions because they contain weak ft bonds. Two 

The oxidation and reduction of alkynes, reactions that also involve addition, are discussed in Chapter 12. 

Because sp hybridized C - H bonds are more acidic than sp and sp hybridized C - H bonds, 

What bases can be used for this reaction Because an acid-base equilibrium favors the weaker acid and base, only bases having conjugate acids with p/i(a values higher than the terminal 

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P Volume 1,1991,283 pp. 109.50/ 69.50 ISBN 1-55938-180-9 CONTENTS Introduction to the Series An Editor s Foreword, Albert Padwa. Preface, Brian Halton. Strain in Organic Chemistry A Perspective, Brian Halton. Gem-Dihalocyclopropanes in Chemical Synthesis, Martin G. Banwell and Monica E. Re-um. 1-Halo- and 1, 2-Dihalocyclopropenes Useful Synthetic Intermediates, Mark S. Baird. Cyciization and Cycloaddition Reactions of Cyclopropenes, Albert Padwa and Glen E. Fryx-ell. New Synthetic Pathways From Cyclobutanones, Edward Lee-Ruff. Cyclic Alkynes, Enynes and Dienynes A Synthetic Challenge, Herbert Meier. Index. 

Rawal and Thadani [160] have taken advantage of alkynes as excellent insertion partners in Pd(II)-catalyzed allylations. Interestingly, the Pd(II) species present in the medium after alkyne insertion into allyl chlorides or bromides can serve for a sequential Wacker-Tsuji oxidation upon introduction of CuCl, oxygen, and water to the reaction medium to give y-halo /-fy-cnones 220 in good yields (Scheme 91). If phenylacetylene is used as an alkyne l-phenyl-pent-2-ene-l,4-dione can be isolated in 77% yield as the result of a subsequent oxidative hydration of the y-halo P,y-enone 220. 

The most important of the methods of synthesis of C-vinylpyrroles is direct introduction of the vinyl group into pyrrole and indole rings by addition of pyrrole or indole to alkynes or substitution reactions at the double bond. Such processes preclude the need for a prior functionalization step, making the overall chemical transformations highly effective. 

CHAPTER 6 Reactions of Alkynes Introduction to Multistep Synthesis... 

The Diels-Alder reaction of oxazoles with alkenes, alkynes, and heterodieno-philes has become a valuable tool for the construction of highly substituted pyridines, furans, and other heterocycles and has now been exploited for the synthesis of diverse compounds from pharmaceuticals to complex natural products. These reactions have been extensively reviewed. The purpose of this chapter is to provide an introduction to the use of oxazoles in Diels-Alder cycloadditions and an update on these reactions since 1985. 

Direct introduction of sp carbon to alkynes by the reaction of Cu acetylides with aryl and alkenyl halides to form arylalkynes and alkenylalkynes is known as the Castro reaction [1]. Later it was found that coupling of terminal alkynes (1-alkynes) with halides proceeds more smoothly by using Pd catalysts. There are two methods of Pd-catalyzed coupling, hi 1975 direct coupling of 1-alkynes catalyzed by a phosphine-Pd(O) complex in the presence of amines was reported by Heck and Cassar as an extension of the Heck reaction to 1-alkynes [2,3]. In the same year, Sonogashira and Hagihara found that the addition of Cul as a co-catalyst gave better results, and the Pd(0)-CuI-catalyzed reaction is called the... 

As noted in the introduction to this section, the insertions of alkynes and alkenes into metal-boron bonds appear to be involved in catalytic additions of borane reagents to alkenes and alkynes. One direct observation of the insertion of an alkyne into a metal-boron bond has been reported, and this reaction is shown in Equation 9.91. In another case, the reaction of an olefin with a metal-boryl complex generated products consistent with the... 

Addition reactions of alcohols to alkenes and alkynes have already been provided (Chapter 6) and a few more are shown in Table 8.6. Further, although many more addition reactions will be encountered later in the text (when the functional group with which the alcohol, enol, or phenol reacts is discussed in more detail), an introduction to some of the more common reactions is provided in Table 8.6. The table presents some of the partners of addition reactions with alcohols, enols, and phenols and the products they form together. The reactions shown are typical and, as such, are briefly discussed. 

CHAPTER 7 The Reactions of Alkynes An Introduction to Multistep Synthesis 299... 

Within the area of alkyne-substituted cluster chemistry by far the most common structural arrangements found are clusters in which the alkyne caps a triangular cluster either in a parallel or perpendicular mode, as described in the introduction to this section. This area of chemistry has been reviewed and particular attention has been paid to the chemical transformations that could occur during catalytic reactions. Table Z lists the /i3-77 - -alkyne triruthenium and triosmium clusters reported, whereas Table 3 lists the -L-alkync clusters. 

The introduction of sulfur moieties to unsaturated hydrocarbon compounds is an important synthetic strategy in the preparation of bioactive compounds. In particular, the use of alkynes enables the facile synthesis of alkenyl sulfides that are stereochemically as well as regiochemically defined structures. Given the important role of catalysts in the stereospecific addition of sulfur-containing reagents to alkynes, the following four sections are devoted to hydrothiolation, bisthiolation, carbothiolation, and related reactions. 

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