Synthesis of alkynes

Acetylene Synthesis by Adding H O to CaC2 (calcium carbide) Sample reaction 17-1 

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These compounds are sources of the nucleophilic anion RC=C and their reaction with primary alkyl halides provides an effective synthesis of alkynes (Section 9 6) The nucleophilicity of acetylide anions is also evident m their reactions with aldehydes and ketones which are entirely analogous to those of Grignard and organolithium reagents... 

A useful synthesis of alkynes and particularly of terminal ( )-enynes results from the insertion of the readily formed ( )-l,2-dichloro-l-lithioethene (68) into organozirconocene chlorides (Scheme 3.17). An intermediate ( )-2-chloroalkenyl zirconium species 69 undergoes anti-elimination of zirconocene dichloride to yield terminal alkynes 70 [38]. 

Cross-Coupling Reactions of Allenes Producing Compounds with an Intact 1,2-Diene Moiety 849 Cross-Coupling Reactions of Allenyl Halides 849 Cross-Coupling Reactions of Allenylmetal Compounds 856 Cross-Coupling Reactions of a-Substituted Allenes 860 Cross-Coupling Reactions of Allenes at the Central Position 862 Synthesis of Alkynes 870 Miscellaneous Reactions 872 Conclusion 873... 

Muller S, Liepold B, Roth GJ et al (1996) An improved one-pot procedure for the synthesis of alkynes from aldehydes. Synlett 6 521-522... 

A particularly interesting example is the synthesis of alkyne-bridged oligomers and polymers, which are attractive materials for optical and electronic applications. Bunz and coworkers were able to modify the Mortreux catalyst system [Mo(CO)6 and a suitable phenol]11 and reaction conditions to perform acyclic alkyne metathesis of 1,4-dipropynylated benzenes to produce high-molecular-weight poly(p-... 

The reactivity order also appears to correlate with the C-X bond energy, inasmuch as the tertiary alkyl halides both are more reactive and have weaker carbon-halogen bonds than either primary or secondary halides (see Table 4-6). In fact, elimination of HX from haloalkenes or haloarenes with relatively strong C-X bonds, such as chloroethene or chlorobenzene, is much less facile than for haloalkanes. Nonetheless, elimination does occur under the right conditions and constitutes one of the most useful general methods for the synthesis of alkynes. For example,... 

A clean and reagent-free generation of highly strained cycloalkynes from bi-3//-diazirin-3-yls has been described.44 A new synthesis of alkynes has been achieved by... 

Alkynes undergo stoichiometric oxidative reactions with Pd(II). A useful reaction is oxidative carbonylation. Two types of oxidative carbonylation of alkynes are known. The first one is the synthesis of alkynic carboxylates 211 by the oxidative carbonylation of terminal alkynes using PdCty and CuCty in the presence of a base [127]. Dropwise addition of the alkyne is recommended as a preparative-scale procedure of this reaction, in order to minimize the oxidative dimerization of alkynes as a competitive reaction [128]. The reaction has been applied to the synthesis of the intermediate 213 of the carbapenem 214 from the terminal alkyne 212 [129],... 

The (dipyridin-2-ylmethyl)amine-derived palladium(n) chloride complex 30 has been found to be a highly efficient catalyst for the synthesis of alkynes in water or in iV-methylpyrrolidone and of diynes in the absence of reoxidant <2005EJOC4073>. 

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... 

Two different approaches are commonly used for the synthesis of alkynes. In the first, an appropriate electrophile undergoes nucleophilic attack by an acetylide ion. The electrophile may be an unhindered primary alkyl halide (undergoes Sn2), or it may be a carbonyl compound (undergoes addition to give an alcohol). Either reaction joins two fragments and gives a product with a lengthened carbon skeleton. This approach is used in many laboratory syntheses of alkynes. 

Chapter 9 covered a synthesis of alkynes by a double dehydrohalogenation of dihalides. A student tried to convert... 

The anthracyciinone class of anticancer compounds (which includes daunomycin and adriamycin) can be made using a mercury (I I )-promoted alkyne hydration. You saw the synthesis of alkynes in this class on Chapter 9 where we discussed additions of metallated alkynes to ketones. Here is the final step in a synthesis of the anticancer compound deoxydaunomycinone the alkyne is hydrated using Hg2+ in dilute sulfuric acid the sulfuric acid also catalyses the hydrolysis of the phenolic acetate to give the final product. 

DIETHYL (DICHLOROMETHYL)PHOSPHONATE. PREPARATION AND USE IN THE SYNTHESIS OF ALKYNES (4-METHOXYPHENYL)ETHYNE (Phosphonic acid, (dichloromethyl)-, diethyl ester to prepare Benzene, 1-ethylnyl-4-methoxy-)... 

DIETHYL (DICHLOROMETHYL) PHOSPHONATE. PREPARATION AND USE IN THE SYNTHESIS OF ALKYNES (4-METHOXYPHENYL)ETHYNE... 

Alkynes are potentially useful as building blocks in the synthesis of numerous organic compounds, and the use of disubstituted alkynes permits the formation of ortho-disubstituted derivatives. However, the commercial development of alkyne chemistry has been hampered by the high cost of most acetylenes. Indeed, only acetylene and propyne can be regarded as low-cost chemicals. Perhaps recent progress in the synthesis of alkynes (206-209) will lead to further large-scale developments. 

The most widely used Pd-catalyzed alkynylation for the synthesis of alkynes, the Sono-gashira reaction, is the hybrid of alkyne version of the Heck reaction and Cu-promoted Castro-Stephens reaction (Scheme 5.20). 

A similar synthesis of alkynes by reductive elimination of enol phosphates of /3-oxosulfones with sodium in liquid ammonia has been reported. ... 

Halogenation is synthetically useful only with CI2 and Br2, because the addition of I2 is often too slow iind the addition of F2 is too explosive. The dichlorides and dibromides formed in this reaction serve as starting materials for the synthesis of alkynes, as we learned in Section 8.10. 

Section 3.1.11.S.3, the double elimination developed by Otera can also be employed in the synthesis 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. 

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