2-Nitroenamines synthesis

Nitroenamines and related compottnds have been used for synthesis of a variety of heterocyclic compottnds. Rajappahassummaiized the chemistry of nltroenamines fseeSecdon4.2. Anga and coworkers have developed the synthesis of heterocycles based on the reacdon of nltropytidones or nltropyrimldmone v/ith nucleophiles. For example, 2-subsdntted 3-nltro-pyridmes are obtained by the reacdon of l-methyl-3,5-dinitro-2-pyridones wiih ketones in the presence of ammonia fEq. 10.82. ... 

The addition of alkoxides to 2-nitro-l-phenylthio-l-alkenes affords P-nitro-aldehyde acetals.276 The reaction of the same nitroalkenes with amines gives nitroenamines.270 They are important intermediates for organic synthesis and are generally prepared by the reaction of nitroalkanes with triethylorthoformate in the presence of alcohols or secondary amines.2"1 0 The methods of Eqs. 4.20 and 4.21 have some merits over the conventional methods, for variously substituted (3-nitro-aldehydes acetals or nitroenamines are readily prepared by these methods. 

A new synthesis of [i-nitroenamines by amination of nitroalkenes with methoxyamine in the presence of base is reported (Eq. 4.23).29... 

Nitroalkenes with potential leaving groups in (3-position such as a dialkylamino, an alkylthio, or a phenylsulfonyl group undergo addition-elimination reactions with nucleophiles. The chemistry of nitroenamines has been extensively investigated, and their potential utility in organic synthesis has been well established.2613 116 Severin and coworkers have developed the addition of elimination reactions of nitroenamines with carbon nucleophiles in 1960-1970, as exemplified in Eq. 4.94.117... 

They have developed direct asymmetric synthesis of quaternary carbon centers via addition-elimination process. The reactions of chiral nitroenamines with zinc enolates of a-substituted-8-lactones afford a,a-disubstituted-6-lactones with a high ee through addition-elimination process, in which (5)-(+)-2-(methoxy methy l)pyrrolidine (SMP) is used as a chiral leaving group (Eq. 4.96).119 Application of this method to other substrates such as a-substituted ketones, esters, and amides has failed to yield high ee. 

JPR711). Also, nitroenamines can be used as the starting materials for the synthesis of thiazoles (85JOC1547) (Scheme 12). 

Nitroenamines have also been used for the synthesis of nitroimidazoles [497] (Scheme 72). 

There are reviews dealing with conjugated nitroalkenes in organic synthesis, " nitroenamines, the oxyalkylation of carbonyl compounds with conjugated nitroalkenes and the use of conjugated nitroalkenes in the synthesis of heterocyclic compounds. In this section mainly the preparation of nitroalkenes starting from alkenes is described. 

Some novel triazolo[4,3-a][l,3,5]triazines have been synthesized by cyclization of imidates with 3-allyl-5-amino-l-phenyl-l,2,4-triazoles <05SC2467>. Derivatives of 1,6-polymethylene-l,3,5-triazinones have been prepared in the reaction of cyclic nitroenamines with isocyanates using a strong base <05M211>. The synthesis and reactions of 5-nitromethyltetrazolo[l,5 [l,3,5]-triazinones have been described <05KGS259 05KGS582>. 

Use ofenamine or iminium electrophiles. In their synthesis of spirotryprostatin B (133), Fuji and co-workers started from rac-3-prenyl-2-oxindole (149) with an interesting enantioconvergent nitroolefination affording the C3-quatemised product 151 ee 78%, Scheme 30). The proline-derived nitroenamine 150 was used with the pyrrolidine section functioning as auxiliary [135, 136]. 

Ethereal a-naphthylmagnesium bromide added rapidly with ice-salt cooling to l-nitro-2-dimethylaminoethylene in tetrahydrofuran, then poured into a mixture of 3%-HCl and ice -> l-(2-nitrovinyl)naphthalene. Y 80%. F. e. s. T. Severin, D. Sdieel, and P. Adhikary, B. 102, 2966 (1969) reaction of 2-nitroenamines with 0X0 compds., also synthesis of 1,3-dinitrobenzenes, cf. ibid. 104, 2856 (1971). 

---