Nitroalkenes crystallization

Seebach and Brenner have found that titanium enolates of acyl-oxazolidinones are added to aliphatic and aromatic nitroalkenes in high diastereoselectivity and in good yield. The effect of bases on diastereoselectivity is shown in Eq. 4.59. Hydrogenation of the nitro products yields y-lactams, which can be transformed into y-amino acids. The configuration of the products is assigned by comparison with literature data or X-ray crystal-structure analysis. 

The photochemical reaction of tetranitromethane with aromatic compounds leads in low yields to 1,3,2-dioxazoles, as products of the nitroalkene cycloaddition of the trinitromethyl intermediate <1995ACS482, 1996ACS29, 1996ACS735>. The cycloaddition products 22a and 22b (0.2-1.8%) were isolated from 1,3-dimethylnaphthalene <1995ACS482>, compound 23a (20%) from 1,2,3-trimethylbenzene <1996ACS29>, and compound 23b (3%) from 1,2,3,4-tetramethylbenzene <1996ACS735>. The structure of all these compounds has been proved by single crystal X-ray analysis (see Section 6.02.3.1). 

The Essential Oils reports that the best general method for making pseudonitrosites is to first dissolve the asarone in petroleum ether, hexane, or even mineral spirits, and then add a concentrated aqueous solution of sodium nitrite. Then after cooling the mixture, acid is slowly introduced, and the whole mixture shaken. The batch is then allowed to stand in the cold, and the crystals filtered out later. With the pseudonitrosite thusly obtained, it s time to move on to the next stage of the reaction scheme, that of producing the nitroalkene B-nitro asarone. Put 10 grams of the pseudonitrosite into any suitable flask which can be... 

The single-crystal X-ray structure of the optimum catalyst (Figure 6.6) was obtained to get an insight into the reaction mechanism and a better understanding of the role of the achiral N ligands. The tridentate Schiff base ligand coordinates in a bidentate mode and the OH of the amino alcohol does not coordinate to the Zn center. Two piperidine molecules occupy two of the coordination sites of Zn, generating a distorted tetrahedral structure. A bifunctional catalyst mode is proposed in which the nitroalkene is activated... 

In the first report [80], an unactivated Z-dienophUe attached to nitroalkene 379 undergoes an intramolecular [4 + 2] cycloaddition in the presence of SnCU to provide a mixture of stable, isolable nitronates 380 and 381 (Scheme 16.75). The major product 380 results from an exo-fold transition structure the minor product 381 forms via the endo-io A transition structure. Nitronate 380 participates in a [3 + 2] cycloaddition with 4-bromophenyl acrylate to afford nitroso acetal 383. The stereostructure of 383 (confirmed by single crystal X-ray structural analysis) reveals that the dipolarophile reacts with nitronate 380 in an exo fashion proximal to the C(4) substituent. This contrasteric result is interpreted in terms of a kinetic anomeric... 

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