Elimination reactions alkyne synthesis

Chapter 8 begins the treatment of organic reactions with a discussion of nucleophilic substitution reactions. Elimination reactions are treated separately in Chapter 9 to make each chapter more manageable. Chapter 10 discusses synthetic uses of substitution and elimination reactions and introduces retrosynthetic analysis. Although this chapter contains many reactions, students have learned to identify the electrophile, leaving group, and nucleophile or base from Chapters 8 and 9. so they do not have to rely as much on memorization. Chapter 11 covers electrophilic additions to alkenes and alkynes. The behavior of carbocations, presented in Chapter 8, is very useful here. An additional section on synthesis has been added to this chapter as well. 

Introduction 392 9-2 Nomenclature of Alkynes 393 9-3 Physical Properties of Alkynes 394 9-4 Commercial Importance of Alkynes 395 9-5 Electronic Structure of Alkynes 396 9-6 Acidity of Alkynes Formation of Acetylide Ions 397 9-7 Synthesis of Alkynes from Acetylides 399 9-8 Synthesis of Alkynes by Elimination Reactions 403 Summary Syntheses of Alkynes 404 9-9 Addition Reactions of Alkynes 405... 

Alkene synthesis is the most important and most widely used reaction in organic chemistry. Many review articles and research papers describe methods for the positioning and stereospecific introduction of carbon-carbon double bonds ". The three most important methods for the synthesis of alkenes described in this chapter are (1) elimination reactions, (2) aUcenation of carbonyl compounds and (3) reduction of alkynes. 

The methods for the synthesis of alkynes have been extensively reviewed in the past 20 years two books, which deal particularly with the preparative aspects of alkyne chemistry, have been published. Except for the syntheses of acetylene and propyne, which are prepared in technical processes from carbides, from methane by oxidation, or by electric arc processes, all carbon-carbon triple bonds must be generated by an elimination reaction. Again, as in the synthesis of alkenes, the most important is the de-hydrohalogenation. 

Alkynylsilanes—reactive precursors and versatile synthons for various reactions—can be obtained mainly by silylation techniques of metallated alkynes (including Grignard derivatives), or by elimination reactions of halogenated alkanes and alkenes in the presence of a silylating agent. The main classes of alkynylsilanes will be discussed as well as some derivatives which may be of further interest to organic synthesis. 

Synthetically useful alkynes can be obtained from 1,2-dibromoalkanes using a variety of bases. Ohgiya et al. developed the DBU promoted elimination reaction of 1,2-dibromoalkanes having an oxygen functional group at C3 [43]. Reaction of 1,2-dibromide 134 having PMB ether at C3 with DBU in DMF gave alkyne 135 in 73% yield. This intermediate was employed for the synthesis of sapinofuranone B (136) (Scheme 7.30). 

Alkenes and Alkynes I Properties and Synthesis. Elimination Reactions of Alkyl Halides 291... 

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