Ionic Elimination of Nitro Compounds

The alkylation of dianion of methyl 3-nitropropionate requires 5 equiv of HMPA. HMPA is a listed mutagen and should not be used in industry or in academia. l,3-Dimethyl-3,4,5,6-tetra-hydropyrimidine (DMPU)164 and quinuclidine IV-oxide (QNO)165 are recommended as replacements of HMPA (Eq. 7.119). 

The reaction shown in Eq. 7.120 has been applied to a total synthesis of (+)-brefeldin-A.166 

Esters and ketones bearing P-nitro groups can be prepared in many ways. For example, the Diels-Alder reaction of methyl P-nitroacrylate is one typical case. Various cyclic dienes are prepared by this route, and the reactions of Eq. 7.121167 andEq. 7.122168 are exemplified. 

Another approach is the Michael addition to ethyl P-nitroacrylate, as shown in Eq. 7.123, which has been used in the synthesis of a-methylenebutyrolactone, a moiety characteristic of many sesquiterpenes.169 

The Michael addition of nitroalkanes to alkenes substituted with two electron-withdrawing groups at the a- and P-positions provides a new method for the preparation of functionalized alkenes. Although reactions are not new,170 Ballini and coworkers have used this strategy in the synthesis of polyfunctionalized unsaturated carbonyl derivatives by Michael addition of nitroalkanes to enediones as shown in Eqs. 7.124-7.126.171 Success of this type of reaction depends on the base and solvent. They have found that DBU in acetonitrile is the method of choice for this purpose. This base-solvent system has been used widely in Michael additions of nitroalkanes to electron-deficient alkenes (see Section 4.3, which discusses the Michael addition).172 

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