Nitrostilbenes, reactions with

As another example of nitrene formation, the reaction of o-nitrostilbene (96) with CO in the presence of SnCU affords 2-phenylindole (97). The reaction is explained by nitrene formation by deoxygenation of the nitro group with CO, followed by the addition of the nitrene to alkene. Similarly, the 2//-indazole derivative 99 was prepared by reductive cyclization of the A-(2-nitrobenzyli-dene)amine 98[89]. 

The reactions of /J-methoxy-a-nitrostilbene (82) with anionic sulphurated nucleophiles159 showed UV/VIS spectroscopic evidence for the presence of the intermediate 83 in the formation of the substitution product (84) illustrated in Scheme 36. 

The aldehydes 3 were synthesized either by Vilsmeyer formyladon of 2 or by reaction of 4-fluorobenzaldehyde with a secondary amine (20). The stilbenes 4 were formed from the corresponding 4-dialkylamino-benzaldehydes either by the Homer-Emmons reaction with 4-nitrobenzyl-(diethyl)phosphonate (prepared by the Arbuzov reaction of a-bromo-4-nitrotoluene) or with 4-methylsulfonylbenzyl(diethyl)phosphonate (prepared in three steps from 4-methylthiobenzylaicohol) (21). A few nitrostilbene compounds were synthesized by heating aldehyde 3 with 4-nitrophenylacetic acid in the presence of piperidine. 

According to Pitacco, Valentin and coworkers secondary ketoenamines react generally with nitroolehns to give alkyl- and aryl-substituted tetrahydroindole-7-ones under thermodynamic control in good yield without any catalyst, if the a-ketoenamine is an N-alkyl derivative. The course of the reaction depends on the substituents and the conditions which result in different cleavage or rearrangement reactions. In the case of a-nitrostilbene a Michael adduct is obtained in low yield. If, however, for example, 1-nitrocyclopentene is used in the reaction with iV-t-butylenaminone under kinetic control, an unstable [4 -i- 2]cycloadduct can be isolated. The reaction clearly demonstrates the concurrence of Michael addition and subsequent cyclization to 7-indolones... 

A kinetic study of the reaction of j8-methoxy-Q -nitrostilbene with cyanamide (NH2CN) in DMSO-H2O (1 1) over the pH range 8.5-12.4 has demonstrated that the anion ( NHCN, pA a = 11.38) rather than the neutral amine is the reactive species. Attempts at monitoring the reaction with the neutral NH2CN at low pH were unsuccessful... 

The synthesis and characterization of the dye-labeled silicone particles with the core-shell architecture was described [18]. In the first step, the chlorobenzyl-functionabzed core was formed via co-condensation of MeSi(OMe)j and trimethoxy-chlorobenzylsilane (ClSi(OMe)3) in the presence of benzetho-nium chloride under basic conditions. Next, a nonfunctional homogeneous shell was formed by the addition of variable amounts of MeSi(OMe)j. The obtained core-shell particles were coated with a hydrophobic surface layer by the end-cap-ping reaction with Me SiOMe and (Me Sil NH, and isolated from the surfactant. This procedure results in the well-defined silicone nanoparticles having a chlorobenzyl-functionahzed core of 10 nm in size that is surrounded with a non-functional-ized protective shell of the thickness in the range 0-3.2 nm. The dye labels (orfho-nitrostilbene (ONS), rhodamine B, coumarin 343, and pyrene) were chemically attached to the core-shell particles by an esterification reaction of the cesium salt of the chromophores with chlorobenzyl functions present in the core. 

It was also found that bromonitrophenylmethane (375) reacted with sodium aryl-methanenitronate (374) in DMSO to give the isoxazoline iV-oxide (369) in 60% yield. Both reactions probably involved the formation of a vicinal dinitroethane derivative (376), which lost nitrous acid to give cfs-a-nitrostilbene (368). As mentioned, the reaction of (368) with (374) gave the isoxazoline iV-oxide (369). 

If the nitro group is located at the ethylene fragment, one-electron transfer initiates dimerization of the developing anion-radicals. a-Nitrostilbene, w-methyl-co-nitrostyrene, and a-nitro-p-ferrocenylethylene give anion-radicals, which dimerize spontaneously. It is interesting to compare reactions of cyclooctatetraene dipotassium (C8HgK2) with a-nitro and a-cyano ferrocenylethylenes (Todres and Tsvetkova 1987, Todres and Ermekov 1989 Scheme 3.4). 

The reactivity toward singlet oxygen [238,454] should be taken into consideration if triplet states are involved (either as intermediate or as sensitizer) on irradiation of air- or oxygen-saturated solutions. Benzaldehyde, hydroperoxides, and dioxetanes have been found as products from the reaction of stilbenes with reactive oxygen species [464,465]. A rearrangement reaction has been reported for nitrostilbenes formation of a-oximinoketones, typical for / -nitrostyrenes, which may be accompanied by cleavage products [466],... 

The Cadogan reaction refers to the deoxygenation of o-nitrostyienes 1 or o-nitrostilbenes with trialkyl phosphite or trialkylphosphine and subsequent cycliza-tion of the resulting intermediate nitrene 2 to form ii oles 3. The Sundberg indole synthesis refers to the synthesis of indoles 3 via either thermolysis or irradiation of o-azidostyrene 4 via the intermediacy of nitrene 2. 

Various catalyst types were tested with a wide variety of substrates. For example, p-iodonitrobenzene and styrene react according to the Heck cross coupling to p-nitrostilbene with a yield of 99%. This situation is similar for many other reactions of styrene and methylacrylate with other reactants containing iodine and bromine. On the other hand, chlorobenzene reacts with styrene only in trace amounts. 

Synthesis of N,N-diethanol-4 -amino-4-nitrostilbene (16). A mixture of of 4-bromo-N,N-diethanolaniline (0.872 g, 3.35 mmol), 4-nitrostyrene (0.500 g, 3.35 mmol), Pd(OAc)2 (0.0752 g, 0.335 mmol), tri-o-tolyl phosphine (0.204 g, 0.670 mmol), and Et3N (0.513 mL, 3.685 mmol) in DMF was heated in a screw tapped tube purged with argon at 90 C for 48 h. The reaction mixture was cooled, filtered, and poured into ice cold water. The organic layer was extracted with EtOAc. The organic extract was dried over MgS04 solvent removed in vacuo. Stilbene... 

Synthesis of nitrostilbene polyurethane 19. A20mLheavy walled glass vial was charged with diol 16 (0.1889 g, 0.575 mmol) and 5 mL of dry DMF. Diisocyanate 17 (0.2449 g, 0.748 mmol) in 5 mL of DMF was added. Two drops of Et3N was added to facilitate the polymerization. The polymerization mixture was stirred at 90 X, yielding an orange-r viscous solution. The reaction was stopped after 48 h and added dropwise into cold methanol. Polymer 19 precipitated out as an orange-red solid powder. It was reprecipitated and washed with methanol. UV ... 

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