Nitronates Preparations acylations

Preparation of a-fluoro ketones or aldehydes can also be achieved by cerium ammonium nitrate oxidation of the corresponding silyl nitronates. C-acylation compounds derived from nitroalkanes can be... 

Nitronate anions react with (jl-allyl)cobalt complexes prepared from acylation of 1,3-dienes by acetylcobalt tetracarbonyl to produce nitro enones (Eq. 5.50).74... 

The formation of derivatives of 2,3,6,8-tetraazabicyclo-[3.2.1]3-octene (425) arises from an intramolecular nucleophilic addition to the nitrone group of hydra-zone (424). Compound (424) was prepared by reaction of 2-acyl-3-imidazoline-3-oxides (423) with hydrazine. From the cis- and frans-derivatives (424), exo- and enr/o-isomers (425) were obtained (Scheme 2.197). The reaction of intramolecular cyclization does not occur in cases with monosubstituted hydrazones (316). 

Finally, the fourth approach (path d) involves the generation of conjugated nitro olefins C from the starting AN by known methods. The latter are involved in the conjugated [1,4]-addition to give target nitronates. This process is of most importance for the synthesis of six-membered cyclic nitronates (see Section 3.2.1.2.2). This method was also used to prepare a small series of boryl-, silyl-and acyl nitronates (see Sections 3.2.3 and 3.2.4). It is beyond reason to believe that all possibilities of the approach (d) are exhausted by these examples. 

There is also evidence that conjugation of the nitronate fragment with jt systems can stabilize acyl nitronates. For example, Perekalin and coworkers (224) isolated a very stable nitronate (63a), which was prepared by acetylation of l,4-dinitrobut-2-ene salts (65) in a mixture with the corresponding C-acylation product (66) (Scheme 3.66), by column chromatography. 

Even more stable acyl nitronates (68) were prepared from conjugated nitro-alkenes (67) (Scheme 3.67) (224). Nitronates (68) were characterized by elemental analysis, mass, and IR spectroscopy. 

The chemistry of acyl nitronates derived from secondary AN has received much more attention. Yoshikoshi and coworkers (226-228) developed a reliable procedure for the synthesis of these derivatives from readily available precursors (ketones and a-nitroalkenes), they demonstrated that the resulting acyl nitronates (123) are convenient reagents for the preparation of various heterocyclic and acyclic derivatives (226) (Scheme 3.104). 

An identical rearrangment can be arrived at tiirou acylation of N-methyl nitrones," conveniently prepared from the kemne (155 to 156), althougb the process is apparently restricted to cyclic substrates, nnally a similar one-pot procedure for conversion of ketoximes to a-acetoxy ketones under the conditions shown (157 to 158), allows the transformation to be carried out simply and efficiently. In this case rearrangement produces a-acyloxyenimides, whose hydrolysis provides Ae keto equivalent. 

Optically active tricyclic isoxazolidine 105, a precursor to (-)-rosmarinecine, was prepared from racemic hydroxy-nitrone 103 through a hydrolase-catalyzed kinetic resolution (KR). In particular, Candida antarctica lipase, fraction B (CAL-B), effectively catalysed the KR of ( )-103 in the presence of the acyl donor 104 in MeCN at 0-5 °C. The generated (R)-ester underwent a fast intramolecular 1,3-DC to 105 under the reaction conditions <05CC2369>. 

Vicinal N-alkylamino-alcohols were prepared by acylation-rearrangement of nitrones, followed by hydride reduction (Scheme 64).146... 

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