Dehydrohalogenation by sodium amide

Dehydrogenation of hydrazo compounds with bromine, 32, 16 Dehydrohalogenation by sodium amide, 30, 72... 

Dehydrohalogenation with sodium amide also provides a useful method for closing an aziridine ring, as illustrated by the preparation of N-ethylallenimine (I -ethyl-2-methylenaziridine). ... 

Double dehydrohalogenation (Section 9 7) Reaction in which a geminal dihahde or vicinal dihahde on being treated with a very strong base such as sodium amide is converted to an alkyne by loss of two protons and the two halogen substituents... 

The synthesis of 1-ethoxy-1-butjme has been reported previously, but the preparations have required multistep sequences. Two of the procedures use 1,2-dibromo-l-ethoxy butane which is dehydrohalogenated in two successive steps, first by an amine base and then by either powdered potassium hydroxide or sodium amide no yields are given. The... 

By using sodium amide in ammonia, ethynyl-Ai-methylpyrazoles 15a-c were synthesized by dehydrohalogenation of dichlorides 13a-c, 14a-c in 60-85 % yields, calculated on acetylpyrazoles 12a-c (Table VTT). 

Sodium amide has been extensively used in the synthesis of a large number of acetylenic compounds by dehydrohalogenation. An example is ... 

A triple bond may be formed by dehydrohalogenation of dihalides and olefinic halides of the general types RCX= CHj, RCH= =CHX, RCH= =CXR, RCHXCHjX, RCHXCHXR, RCHjCHX, and RCXjCHjR. The choice of a base depends somewhat on the position desired for the triple bond in the product. Sodium amide tends to rearrange the triple bond toward the end of the chain," and potassium hydroxide favors reverse isomerization toward the center of the chain,Although neither rearrangement is dependable from a synthetic standpoint, it is best to choose the base favoring the desired product. 

Mono- and di-alkylacetylenes are prepared from sodium alkydes and primary alkyl halides which lack branching on the second carbon atom. The branched primary halides as well as secondary and tertiary halides undergo dehydrohalogenation to olefins by the basic alkyde. The alkydes are best prepared from the acetylenes and sodium amide in liquid ammonia.The yields of 1-alkynes are frequently 70-90% when alkyl bromides are employed as alkylating agents. Dialkylacetylenes... 

Two dehydrohalogenations involving ether cleavage are described by the Jones group. One is the preparation of ethoxyacetylene from diethylchloroacetal. A suspension of sodium amide in liquid ammonia was agitated manually in a flask... 

In dehydrohalogenation reactions, hydrogen and halogen are the atoms eliminated from adjacent carbons. Bases such as potassium hydroxide and sodium amide are the reagents. Both alkenes and alkynes can be synthesized by dehydrohalogenation. 

Dehydrohalogenation [1, 1035-1037, at end]. In a general procedure for the conversion of alkenes into alkynes by bromination and dehydrobromination, Ward and van Dorp recommend sodium amide and liquid ammonia for the dehydrobromination step.103 The preparation of propargyl aldehyde diethyl acetal is an example ,cb... 

Initial dehydrohalogenation of the w r-dihalide produces a mixture of two bromoalkenes that are not isolated but that undergo a second dehydrohalogenation. The terminal alkyne that results from this step is deprotonated (because of its acidity) by the third mole of sodium amide (see Section 7.9). To complete the process, addition of ammonium chloride converts the sodium alkynide to the desired product, 1-butyne. 

The most often applied and most reliable procedure to obtain a cycloalkyne (Fig. 2, bottom), as originally developed by Brandsma in the Netherlands, [11], involves the stepwise double dehydrohalogenation of a vicinal dihalogenide (typically bromide), which can be readily obtained from a cyclic alkene upon treatment with elemental halogen. In this case, a first E2-elimination may take place under mildly basic conditions, forming an intermediate alkene, which in turn will undergo a second elimination upon treatment with a strong base like sodium amide or potassium ferf-butoxide. More conveniently even, in many cases both... 

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