Alkynes double elimination from dihaloalkanes

Double Elimination from Dihaloalkanes to Give Alkynes X X... 

The two basic methods used to prepare alkynes are double elimination from 1,2-dihaloalkanes and alkylation of alkynyl anions. This section deals with the first method, which provides a synthetic route to alkynes from alkenes Section 13-5 addresses the second, which converts terminal alkynes into more complex, internal ones. 

In Summary Alkynes are made from vicinal dihaloalkanes by double elimination. Alkenyl halides are intermediates, being formed stereospeciflcally in the first elimination. 

The other major dehalogenation pathway involves elimination of two halogens, leaving behind a pair of electrons that usually goes to form a carbon-carbon double bond. Where the pathway involves halogens on adjacent carbons, it is known as vicinal dehalogenation or reductive / -elimination. The fine dashed arrows in Fig. 4 illustrate this process for PCE. Note that this pathway can produce alkynes from vicinal dihaloalkenes [88,94,95], as well as producing alkenes from vicinal dihaloalkanes [96,97],... 

The elimination route to alkynes involves removal of two moles of hydrogen halide by strong base from a dihaloalkane. The most common kind of sequence involves forming the dihaloalkane by addition of halogen to an alkene double bond. Because you already know how to make alkenes, you now have access to alkynes in the following way ... 

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See also in sourсe #XX -- [ ]

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