1.8- Diazabicyclo undecene

In chapter 2, Istvdn Hermecz has summarized our knowledge of the chemistry of the pyrimidoazepines, in particular that of diazabicyclo-undecene (DBU). 

The same authors have also reported the application of green solvents in additions of terminal alkynes to aldehydes in the presence of Zn(OTf)2 and l,8-diazabicyclo[5,4,0]-7-undecene (DBU, Scheme 109).287 The reactions proceeded very slowly, but afforded desirable alcohols 195 in moderate to good yields. 

In the presence of proton and/or Lewis acid and strong nucleophiles bicyclo[3.2.0]heptan-6-ones are converted to 3-substituted cycloheptanones (Table 15). Bicyclo[3.2.0]heptan-6-ones rearrange to give 3-iodocycloheptanones on treatment with iodotrimethylsilane. Zinc(II) iodide or mercury(II) halides as catalysts enhance the rate and the selectivity of the reaction.31 If a second, enolizable carbonyl group is present, an intramolecular alkylation may follow the ring enlargement under these reaction conditions.32 Consecutive treatment with tributyltin hydride/ 2,2 -azobisisobutyronitrile affords reduced, iodo-free cycloheptanones, whilst treatment with l,8-diazabicyclo[5.4.0]undecene yields cycloheptenones.33 Similarly, benzenethiol adds to the central bond of bicyclo[3.2.0]heptan-6-ones in the presence of zinc(II) chloride and hydrochloric acid under anhydrous conditions to form 3-(phenylsulfanyl)cycloheptanones.34... 

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... 

B-80MI11514 Technical Bulletin 8-333, DBU l,8-diazabicyclo[5.4.0]undecene-7 , San-Abbott... 

Eghbali et al. [185] have reported the details of a highly efficient method for converting alkenes and C02 into CCs directly in water, by using N-bromosuccin-imide (NBS) together with l,8-diazabicyclo[5.4.0]undecen-7-ene (DBU), or a catalytic quantity of bromide ion together with aqueous H202. 

MICHAEL ADDITIONS Alumina. Aluminum chloride. Cesium fluoride-Silicon(lV) cthoxidc. 1,4-Diazabicyclo[2.2.2]octanc. l,8-Diazabicyclo[5.4.0]-7-undecene. Ketene r-butyldimethylsilyl methyl acetal. Lithium acetylides. (S)-( + )-2-Mcthoxymethylpyrrolidine. Methyl lithiodithioacetate. Methyl (phcnylsulfinyl)acetate. Methyl 2-trimcthylsilylacrylate. Nickel carbonyl. Organocopper reagents. 8-Phenylmcnthol. Phenyl 2-(trimethylsilyl)ethynyl sulfone. Tetra-n-butylammonium fluoride. Tiianium(IV) chloride. 3-Triisopropylsilylpropynyllithiuni. Zirconium(IV) n-propoxiilc... 

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. 

B3LYP = Becke s 3-parameter hybrid with Lee Young and Parr s correlation functional 5 = Chemical shift of NMR signal in ppm DBU = l,8-diazabicyclo[5.4.0]-7-undecene eq = Equivalent NMR = Nuclear magnetic resonance THE = Tetrahydrofuran. 

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