3- Nitro-2//-chromenes

The Michael aclcliQon of oxygen-nucleophiles followed by subsequent cyclizadon or cycloaddidon provides an important method for the preparadon of oxygen-heterocycles such as tetrahydrofurans For example, 3-nitro-2//-chromenes bearing various snbsdtnents are prepared by the reaction of snbsdtnted sahcylaldehydes with nitro ilkenes fEq 4 14 ... 

The electron impact mass spectra of series of 2-aryl-3-nitro-2//-chromenes and 2-aryl-3-nitrochromanes with varying functionalities have been reported101. The molecular ion is always of considerable intensity. Loss of NO2 from M+ is responsible for the base peak in the nitrochromenes101. In contrast, the [M — HONO]+ is apparently the more abundant ion in the nitrochromanes. This unusual loss of HONO is always observed in the metastable time-frame101. 

Chemical ionization MS of 2-aryl-3-nitro-2//-chromenes and 4-hydroxy-3-nitroflavans have been studied using methane and ammonia as reagent gases102. The behaviour of 2-aryl-3-nitro-2//-chromenes was found to resemble that of aromatic nitro compounds. Thus, the methane spectra are characterized by the MH+ ions, whereas the ammonia... 

Recently, Chen and coworkers found that readily available (2S,4R)-4-hydro>qqDrolinamide 44 in combination with 4-nitrophenol as a cocatalyst effectively catalysed an asymmetric domino oxa-Michael/Henty reaction of salicylaldehyde derivatives 50 with trans-p-nitro olefins 51 to afford 3-nitro-2//-chromenes 52 in moderate to excellent yields and with up to 90% enantiomeric excess under mild conditions (Scheme 10.10). With the corresponding hydrojgr group-free prolinamide a significant reduction in... 

A soln of N-(2-nitrovinyl)morpholine and o-hydroxybenzylalcohol in acetic anhydride refluxed for 2 h - 3-nitro-2-chromene. Y 62%. F.e. inch 3-carbalkoxy, 3-formyl- and 3-acyl-derivs., and alternative method s. L. Rene, Synthesis 1989,69-70. 

The high diastereoselective synthesis of multifunctionalized 3,4-dihydro-coumarins bearing a quaternary stereocenter was developed through tandem Michael additions of indole and its derivatives (1-methyl, 2-methyl, 4-methoxy, 5-methoxy, 5-bromo, 6-benzyloxy) to 3-nitrocoumarines (3-nitro-chromen-2-one, 6- and 7-methyl-3-nitro-chromen-2-one) followed by methyl vinyl ketone in a one-pot step. For the tandem Michael additions, after the first Michael reaction of indole (2) with 3-nitrocoumarine (51) catalyzed... 

Finally, Sankararaman et al. have reported the synthesis of chiral nitro-chromenes on the basis of an asymmetric domino Michael-Henry reaction followed by dehydration, involving nitrostyrene and orlho-hydio-xybenzaldehyde. This reaction was catalysed by a novel C2-symmetric bis-(pyrrolidine-triazole)-based organocatalyst and provided only moderate yields (22-40%) and poor enantioselectivities (7-24% ee). 

H-Chromene, 7-methoxy-2,3-dimethyl-application, 3, 881 2H-Chromene, 2-methyl-mass spectra, 3, 603 2H-Chromene, 2-methyl-3-nitro-hydrogenation, 3, 673... 

Reaction of nitro-2f/-chromene derivatives 134 with 135 in methanol at room temperature afforded a mixture of the Z-isomer 136 and tricyclic compound 137, which could be formed by denitrocyclization reaction of the corresponding primarily formed E-isomer and the following dehydrogenation (Eq. 15). The structural identification was based on the MS and H-NMR, however, it is not sufficiently documented and similar examples are not known (91IJC(B)297). 

The reaction with nitroethanol in the presence of di-)i-bntylammmonium chloride in refluxing iropentyl acetate gives 2-unsnbsdtnted 3-nitro-2H-chromene in 50% yield. Some 3-nitro-2H-chromenes display efficient optical second harmonic generadon for nonhnear opdcal apphcations. 

Stereochemical differences are observed between the products of hydrogenation and those of LAH reduction of some chromenes, for example 2-methyl-3-nitro-2H-chromene, as shown in Scheme 10 (73JCS(P2)227). 

Nitroethenes react with 2-hydroxybenzaldehyde under Baylis-Hillman conditions to afford 3-nitro-2/7-chromenes in high yield (Equation 36) <2001TL2717>. Likewise, the polycyclic nitroethenes 62-65 react with 2-hydroxybenzaldehyde to form the corresponding 2-spirocyclic-3-nitro-27/-chromenes in good yield (49-99%) <2001TL2717>. 

M. A. Gal bershtam, N. M. Przhiyalgovskaya, O. R. Khrolova, I. B. Lazarenko, G. K. Bobyleva, and N. N. Suvorov, Photochromic properties of some N-substituted 3,3-dimethyl-6 -nitro-indoline-2-Spiro-2 -2/7-chromenes, Chem. Heterocycl. Cpds., 1977, 1309-1313. 

Bianco, L., Rene, L., Royer, R., Cavier, R., and Lemoine, J. 1977. Stndies of nitro-derivatives of biological interest. XB. Activities of 2-alkyl-3-nitro 2H-chromenes against microorganisms. European Journal of Medicinal Chemistry, 12(4) 385-6. 

Sequential inter- and intramolecular Michael additions are proposed to account for the formation of 3-nitro-4-nitromethylchromans from the reaction of nitroalkenes with 2-(2-hydroxyaryl)-l-nitroethene derivatives 16 that proceeds with high stereoselectivity. Treatment of the products with base yields chromenes <03TL3813>. 

In a quantitative study of the photostability of spiropyrans, Malkin et al.11 concluded that the photodegradation quantum yield d is independent of the heterocyclic part and is determined instead by the structure of the chromene part of SPs. According to these authors, photodegradation of nitro-substituted SPs originates from the reaction of the cis-cisoid X isomer with solvent or impurities (Scheme 6) ... 

The V1/2 values obtained for dioxane solutions (10 4M) of spirobenzopyrans substituted on the chromene moiety are presented in Table 2. In the nitro-substituted spiropyran series (6, 28, and 29), the 6-nitro derivative is usually more stable. OCH3 and CHO substituents are also more stabilizing when on C6 (cf. 6 and 32 30 and 32). Indeed, the electron-donor efficiency of the methoxy group is higher when at C6 as indicated by the Hammett ct constant values, which are -0.76 for the C6 (para) position and -0.39 for the C8 (ortho) position. For the nitro-substituted spiropyrans, the electron-withdrawing character of N02 depends on the substitution position, with Hammett constants of 0.66, 0.78, and 0.80, for N02 at C7, C6, and C8, respectively. 

When salicylaldehyde is heated with a 2-nitrovinylamine (122), 2-amino-3-nitro-2/f-chromenes (123) are formed. A number of cannabichromene-type compounds have been synthesized, in moderate yields, by condensing citral with the 2-lithio-derivative of a 3-methoxyanisole (124 R = H or alkyl). ... 

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