Dihalides acetylene derivs

Ethylene derivatives from 1,2-dihalides Acetylene derivatives from 1,2-ethylene-1,2-dihalides... 

Cupric chloride 1,2-Ethylene-l,2-dihalides from acetylene derivatives... 

Acetylene derivs. via dihalides Terminal acetylene derivs. via 1,1-chlorobromides... 

The reactions of halogenomethylpyridines Table 6.13) with nucleophilic reagents are normal and require no comment is. The familiar reaction of dehydrohalogenation to produce acetylene derivatives is of considerable value in its application to side-chain halogen derivatives of the pyridine series. Its value arises from the possibility of carrying out the sequence of reactions, 2(or 4)-picoline 2(or 4)-styrylpyridine (p. 334) -> 2 (or 4)-styrylpyridine dihalide (p. 349) 2-(or 4)-tolazole. The dehydrohalogena-... 

Other interesting synthetic applications of the ketone-derived enamine alkylation are found in the monomethylation of steroid enamines (249), extension of the benzylation reaction (250) to a ferrocene derivative (251), the use of a-bromoesters (252) and ketones (252) or their vinylogues (25J), in the syntheses of alantolactone (254-256), isoalantolactone (257), and with a bridged bis-enamine (258). The use of bifunctional alkylating agents is also seen in the introduction of an acetylenic substituent in the synthesis of the characteristic fragrant constituent of jasmine (259), the synthesis of macrocyclic ketolactones (260), the use of butyrolactone (261), and the intermolecular or intramolecular double alkylations of enamines with dihalides (262). 

Chromium(II) sulfate is a versatile reagent for the mild reduction of a variety of bonds. Thus aqueous dimethylformamide solutions of this reagent at room temperature couple benzylic halides, reduce aliphatic monohalides to alkanes, convert vicinal dihalides to olefins, convert geminal halides to carben-oids, reduce acetylenes to /raw5-olefins, and reduce a,j3-unsatu-rated esters, acids, and nitriles to the corresponding saturated derivatives. These conditions also reduce aldehydes to alcohols. The reduction of diethyl fumarate described in this preparation illustrates the mildness of the reaction conditions for the reduction of acetylenes and o ,j8-unsaturated esters, acids, and nitriles. 

The requirement for photoinitiation indicates that a radical-chain mechanism must be involved. Chlorination of 1-pentyne carried out in a gas phase reactor at higher temperatures and with higher chlorine alkyne ratios gives both the trans dichloroalkene and the saturated tetrachloro compound derived from addition of a second mole of chlorine.Fair yields of dichloroalkenes, predominantly the cis dihalide, can be obtained from acetylenes by reaction with antimony penta-chloride... 

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