Dehydrohalogenation, with quinoline

Dehydrohalogenation Reactions. Quinoline is sometimes used as a base or solvent for dehydrohalogenation reactions because of its basic properties. A wide variety of substrates, ranging from very simple to quite complex compounds, have been effectively dehydrohalogenated with quinoline. For example, 3-bromo-3-methyl-2-butanone (1) underwent reaction with quinoline to give a mixture of products, 3-methyl-2-butanone (2) and 2-methyl-l-buten-3-one (3) (eq 1). ... 

While the dehydrohalogenation of 3-halo-5a-steroids gives the A -olefin selectively, it has been shown that in the 5j5-series dehydrochlorination of 3j5-chloro compounds with quinoline gives a mixture of A - and A -olefins in a 45 55 ratio. 

Here direct dehydrohalogenation with KOH [49] to give the desired diene poses a particular problem, which can be overcome by applying quinoline [153], or by a change of the type of elimination, by using electrophilic conditions such as catalytic tin tetrachloride at elevated temperatures [154], sulfuric add [155], lithium chloride in N-methylpyridone [156] or hthium bromide in DMF [157]. 

One of the oldest methods of preparing diphenylketene consists in the dehydrohalogenation of diphenylacetyl chloride with tertiary amines. The yield of the ketene was reported as quantitative when tripropylamine was the dehydrohalogenating agent, and considerably less with quinoline, whereas thermal dehydrohalogenation of the acid chloride... 

Telluropheno[2,3-b]quinolines were obtained by dehydrohalogenation of 2,3-dihydro-telluropheno[2,3-A]quinoline 1,1-dihalides with l,5-diazabicyclo[5.4.0]undec-7-ene (DBU) in yields ranging from 12 to 35%. The dihalides were prepared from the 2,3-dihydro tclluropheno[2,3-6]quinolines (p. 374) and /V-bromosuccinimide or iodine in carbon tetrachloride. 

Dehydrohalogenation. This base is a superior reagent for effecting dehydro-halogenation. Truscheit and Eiter were unable to dehydrochlorinate the chloro ester (1) with usual tertiary bases (pyridine, quinoline, N,N-dimethylaniline) but by stirring a mixture with the bicyclic amidine base at 90°, adding ice and sulfuric acid, and working up the neutral fraction, they obtained in 85% yield a 70 30 mixture of cis- and trans-methyl tridecene-lO-yne-12-oate (3). 

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