Lithium nitronates

In general, the Henry reaction proceeds in a non-selective way to give a mixture of anti (erythro) and syn (threo) isomers. Ab initio calculations on the Henry reaction suggest that free nitronate anions (not influenced by cations) react with aldehydes via transition states in which the nitro and carbonyl dipoles are antiperiplanar to each other. This kind of reaction yields anti-nitro alcohols. The Henry reaction between lithium nitronates and aldehydes is predicted to occur via cyclic transition states yielding syn-nitro alcohols as major products (Eq. 3.64).108... 

A convenient and general method has been developed for the synthesis of alkylpyrroles starting from ketones and nitroalkenes via reduction of the intermediate acetic nitronic anhydride as shown in Eq. 10.1. Ketone enolates react with a variety of nitroalkenes to yield the Michael adducts, lithium nitronates, which are trapped with acetic anhydride to give the corresponding acetic nitronic anhydrides. The acetic nitronic anhydrides are easily converted into alkylpyrroles by reduction with Zn(Cu).3... 

Die Henry-Reaktion von sek. Nitro-alkananen mit Cyclohexanonen wird bei hohem Druck mit Tetrabutylammoniumfluorid als Katalysator durchgefuhrt bzw. durch Lithium-a-lithium-nitronate erzwungen. 

The structure of LLB-II is still not secure. However, a reasonable proposal is that it is composed of a complex of LLB and LiOH. A proposed reaction course for an improved catalytic, asymmetric nitroaldol reaction is shown in Figure 25. The key feature of this proposal is the formulation of a discrete complex (II) between LLB and the lithio nitronate. This species is proposed to be a faster-acting reagent than the protio-form. In support of this hypothesis is the observation that treatment of the lithium nitronate (0.9 mol %) generated from nitropropane and butyllithium, with 69g (1 mol %), 2, and nitropropane (83) under similar conditions as those described above, gave comparable results (59% yield, syn/anti, 94/6,94%... 

In related procedures acetyl chloride and acetic anhydride have been used to prepare nitrile oxides from lithium nitronates (86T3825), whereas the nitronic ester (18), prepared by 0-alkylation of the nitroalkane (17), underwent thermal elimination of methanol to generate benzenesulfonylni-trile oxide (19) (Scheme 6) (84H2187). The latter procedure is potentially HAZARDOUS, as the nitronic ester (18) has been reported to be EXPLOSIVE (85JMC1109), and base-induced elimination of methanol from the... 

Reduction of a, -unsaturated nitroalkenes J These nitroalkenes are reduced by lithium tri-.vt c-butylborohydride or by lithium triethylborohydride to lithium nitronates, which are hydrolyzed by dilute acid or by silica, - cl to nitroalkanes (equation I). 

Ketoximes from R CH NOj and R MgBr. Reaction of the Vilsmeier reagent with the lithium nitronate of a nitroalkane activates the -position to attack by Grignard reagents to form ketoximes (equation I). 

The anions of nitroalkanes (nitronates) can be used as precursors in a connective and regiospecific synthesis of tetrasubstituted alkenes. They are easily formed on reaction with LiOMe and undergo oxidative dimerization in the presence of bromine. The resultant 1,2-dinitroalkanes (Scheme 37) participate in a reductive elimination involving an rc1 radical chain mechanism when irradiated in the presence of Na2S, PhSNa or the lithium nitronate derived from 2-nitropropane. 

An alternative procedure (Scheme 38) affords a connective synthesis of unsymmetrical tetrasubstituted alkenes. In this case the lithium nitronate reacted with a 1,1-dinitroalkane to give the 1,2-dinitroalkane intermediate. Reductive elimination was effected by Ca(Hg) in DMF-HMPA. 

Cherest, M., and Lusinchi, X., The Action of Acetyl Chloride and of Acetic Anhydride on the Lithium Nitronate Salt of 2-Phenylnitroethane. Reactivity of the Intermediate Nitrile Oxide as an Electrophile or as a Dipole, Depending on the Nature of the Medium, Tetrahedron, 42 (14) 3825-3840 (1986). (English Abstract). 

The proposed mechanism for the asymmetric nitroaldol reaction catalyzed by heterobimetallic lanthanoid complexes is shown in Scheme 2 [5]. In the initial step, the nitroalkane component is deprotonated and the resulting lithium nitronate coordinates to the lanthanoid complex under formation of the inter-... 

Although the lithium nitronate is first generated, there also appears to be a significant possibility that the aldehyde coordinates to La first... 

Conversion of the nitromethyl to aldehyde by oxidation of the lithium nitronate in aqueous sodium tetraborate with sodium permanganate followed by the usual... 

Three cases of Type la activations illustrate a class of reactions expected to give positive results. The first one is provided by SrnI or ETC processes. Figure 1 shows the chain mechanism of the reaction of lithium nitronate with 4-nitro-benzyl bromide established by Komblum and Russell. This reaction was expected to display sonochemical switching, which was indeed foimd. The mechanism suggests that the sonochemical activation should find its origin either in creating species 1 or 2 (no direct entry to 3 seems plausible). The creation of 1 within a cavitation bubble could result either from high-pressure-promoted electron transfer (activation volumes for some electron transfer reactions may be found in Ref. 9) or local conditions at the interface between the cavitation bubbles and the bxilk solution (Qi. 1). The creation of radical 2 could result from a direct sonolysis of the benzylic C-Br bond (p. 86) but... 

A number of functionalization reactions of nitronates have been described. For example, O-sUylation of nitronate salts is relatively straightforward the most reliable methods involve trapping lithium nitronates (prepared by deprotonating... 

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