Bases 1.8- Diazabicyclo undecene

The elimination of HX from an alkyl halide is a very general reaction and can be accomplished with chlorides, fluorides, bromides, and iodides.232 Hot alcoholic KOH is the most frequently used base, though stronger bases233 (OR, NH2", etc.) or weaker ones (e.g., amines) are used where warranted.234 The bicyclic amidines l,5-diazabicyc o[3.4.0]nonene-5 (DBN)235 and l,8-diazabicyclo[5.4.0]undecene-7 (DBU)236 are good reagents for difficult cases.237... 

Two frequently used amidine bases are DBN (l,5-diazabicyclo[3.4.0]nonene-5) and DBU (l,8-cfiazafciicyclo[5.4.0]undecene-7). 

Chapter S you met the bases DBU (l,8 diazabicyclo[5.4.0]undecene-7) and DBN (l,5-diazabicycio[3.4.0]nonene-5) named in the same way—and you will meet them again in the very next chapter, as they are particularly good bases for the promotion of elimination reactions. 

Bases Alumina, see p-Toluenesulfonylhydrazine. Dehydroabietylamine. 1,5-Diazabicyclo [4.3.0]nonene-5. 1,4-Diazabicyclo[2.2.2]octane. l,S-Diazabicyclot5.4.0]undecene-5. 2,6-Di-/-butylpyridine. N,N,-Diethylglycine ethyl ester, see /-Amyl chloroformate. 2,6-Dimethyl-piperidine. Ethanolamine. Lithium diisopropylamide, see Diphenylsulfonium isopropylide. Lithium nitride. Magnesium methoxide. N-Methylmorpholine. Piperidine. Potassium amide. Potassium hydroxide. Potassium triethylmethoxide. Pyridine. Pyrrolidine. Sodium methoxide. Sodium 2-methyl-2-butoxide. Sodium thiophenoxide. Thallous ethoxide. Triethyla-mine. Triphenylphosphine, see l-Methyl-2-pyrrolidone. 

Dimedone provides diazo dimedone (135) with -benzoic acid sulfonylazide (84%) and with p-tolyl sulfonylazide (96%). Weak nucleophilic base such as 1,8-diazabicyclo[5.4.0]undecen-7-ene (DBU) has been used as catalyst for the diazo transfer reactions of 1,3-diketones (136 -139).55 A highly efficient methodology in solid state has been developed for the synthesis of a-diazo carbonyl/sulfonyl compounds from 1,3-diketones using tosyl azide. This method avoids any aqueous workup and diazo compounds are obtained via a column filtration over silica gel. 0... 

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