L- -nitroalkenes

A stereospecific total synthesis of polyoxin C and related nucleosides is reported, in which thereacdon of l-Cphenylthioi-l-nitroalkenes v/ith nucleophiles and siibseqiientozono lysis are key reacdons Addidonof potassium trimethylsilanoate to l-Cphenylthioi-nitroalkenes derived from D-ribose followed by ozonolysis gives the cr-hydroxy thioester, which is formed v/ith excellent diastereoselecdvity fScheme 4 5 This conformadon meets the stereo-electronic requirements for andperiplanar addition of the nucleophile with the result of high 5-fS stereochemical bias in the reacdons... 

Jackson and coworkers have used a new approach to the synthesis of fi-hydtoxy-ct-amino acids using farylthio nitrooxiranes. c-Jsopropylideneglyceraldehyde is converted into the corresponding 1-arylthio-l-nitroalkene, which is a key material for stereoselective synthesis of fi,Y-dihydroxyamino acids fScheme 4.6. The key step is stereoselective nucleophilic epoxlda-donof the Tarylthio-Tnltroalkene. Sy)i and ruin epoxides are selecdvely obtained by appropriate choice of epoxidadon reagent." ... 

When D-galacto-l-nitroalkene is used, a 85 15 mixnire of ( 45,55 and ( 4ft,5ft is formed. Preferred attacks of dienes at the most stable cooformers of these nitroalkenes are shovm in Scheme 8.10. °... 

Dithio-l-nitroalkenes are prepared by the reacdon of nitromethane v/ith CS and KOH followed by alkyladonv/ith alkyl halides CEq. 10.84. They are important reagents forsynthesis... 

The stereochemical outcome of these reactions can be rationalized by inferring the transition states 2 and 3 for ( )- and (Z)-l-nitroalkenes, respectively4. 

The stereoselective synthesis of awri-P-amino-a-hydroxy acid derivatives using nucleophilic epoxidation of 1-arytlthio-l-nitroalkenes has been reported (Eq. 4.41).54... 

In a similar way, a-nitroselenides are prepared via the reaction of nitronates with phenylse-lenyl bromide, which gives a new synthetic method of l-nitroalkenes from nitroalkanes.130 The sequence of a-selenation, nitro-aldol reaction, and oxidation provides a useful method for the preparation of nitroalkenes with a hydroxymethyl group (Eq. 5.81).131... 

This strategy is applied to a general method for the preparation of 2,2-disubstituted 1-ni-troalkenes. Conjugate 1,4-addition of complex zinc cuprates to l-nitroalkenes, followed by trapping with phenylselenyl bromide and subsequent oxidative elimination, affords the corresponding 2,2-disubstituted l-nitroalkenes in good yields (Eq. 5.82).132... 

The review by Barrett (Ref. 127) documents synthetic application of hetero-substituted nitroalkenes (see also Chapter 4). 1-Chloro-l-nitroalkenes are readily obtained either by the Henry reaction of chloronitromethane with aldehydes or chlorination of l-nitroalkenes. Dauzonne and coworkers have used 1-chloro-l-nitroalkenes for construction of dihydrobenzo-furan or dihydrobenzopyran frameworks. (Eq. 5.83).133... 

Aromatization is often observed during the Diels-Alder reaction using nitroalkenes. Jung24 and Ono25 have reported that 2-phenylsulfinyl-l-nitroalkenes act as nitroacetylene equivalents in Diels-Alder reactions to give aromatic compounds, as shown in Eqs. 8.14 and 8.15, respectively. 

Reactions of the lithium etiolate of cyclohexanone with E-l-nitroalkenes in the presence of chiral lithium amides have been studied by Seebach and co workers [558], and good diastereo- and enantioselectivities are obtained in a few cases. The tin enolate of TV-propionoyloxazolidinone 6.83 undergoes diastereo- and enan-tioselective Michael reactions when coordinated to chiral amine 2.13 (R = NH-l-Np) [682] (Figure 7.59). Similar reactions show low enantiomeric excesses (5 70%) however, some Michael additions catalyzed by chiral catalysts have shown high selectivities ( 7.16). 

Recently, Fuji and coworkers have reported the enantioselective construction of a highly functionalized bicyclo[4.3.0] system through the Diels-Alder cycloaddition between Danishefsky s diene and an enantiomerically pure a,p-unsaturated sulfoxide substituted at the p-position by an electron-withdrawing nitro group [181,182]. Despite the numerous examples of diastereoselective Diels-Alder cycloadditions described above for enantiomerically pure P-substituted-a,P-unsaturated sulfoxide dienophiles, this is the first report of an enantioselective version of the reaction, where the chiral auxiliary is eliminated under the reaction conditions or during the workup procedure. Thus, the Diels-Alder reaction between optically active 2-alkylsulfinyl-l-nitroalkene (228) and Danishefsky s diene afforded endo and exo cycloadducts (229) and (230) in good yields with high enantiomeric excesses (Scheme 5.73). 

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