Nitroso-olefins

SCHEME 10.42 In situ generated nitroso olefins undergo facile cycloadditions with enol ethers. 

Sullivan, A.B. Electron spin resonance studies of a stable aryl nitroso-olefin adduct, free radical. J. Org. Chem. 1966, 31, 2811. 

The known chemistry of the bisftrifluoromethyOnitroxyl [3i, 34] includes additions to both olefins [75, 36 37] and fluoroolefins [iaddition products with chlorotnfluoroethene or tetrafluoroethene [39] The nitroso denvative, (Cp3)3NONO, reacts with a liimted set of halogenated olefins to add the (CF3)2NO and NO moieties [40]... 

Reactive unsaturated nitroso compounds such as 1112 can also be readily prepared from a-halooximes such as 1111 on treatment with powdered Na2C03 in diethyl ether to give, in the presence of enoltrimethylsilyl ether 1113 or strained olefins such as norbomene and other dienophiles, hetero-Diels-Alder adducts such as 1114 and 1115 in moderate yields [150-155] (Scheme 7.47). 

Main Aspects of Chemistry and Stereochemistry of Cyclic Nitroso Acetals Chemistry of cyclic nitroso acetals or nitrosals (the term was introduced by Prof. Seebach) has attracted interest only after the discovery of the 1,3-dipolar cycloaddition reaction of nitronates with olefins in 1962 by the research group of Prof. Tartakovsky. (Principal data on nitroso acetals up to 1990 were summarized in the review by Rudchenko (395).)... 

Besides, cyclic nitroso acetals have attracted considerable interest because [3+ 2]-cycloaddition of nitronates to olefins provides a simple and efficient procedure for the synthesis of five-membered cyclic nitrosals (see Scheme 3.153). Hence, knowledge of the configurations of these products allows conclusions about the mechanism of this very important process. However, it is impossible to distinguish kinetic and thermodynamic products of [3+ 2]-cycloaddition of nitronates to olefins without studying such a fundamental problem as the stereodynamics of five-membered cyclic nitroso acetals, that is, the ring and nitrogen inversions. 

Entry Nitronate R Olefin R Nitroso acetal Ratio cis/trans Yield, %%... 

The synthesis of nitronates (297) in the presence of electron-deficient olefins (398) produces optically pure nitroso acetals (300) with high optical purity. Interestingly, the use of ethanol as the solvent in the (296— 298) reaction leads to a substantial increase in de compared to CH2CI2 (157). 

Another research group (147) studied the reaction of vinyl ethyl ether with optically pure a-nitroolefin (302) giving rise to enantiomerically pure nitronate (303). The reaction of the latter with an excess of the olefin gradually produces nitroso acetal (304) (Scheme 3.181). 

A method for the preparation of olefins from primary amines is shown in equation 120. Treatment of 2-(4-bromophenyl)ethylamine (358) with acetic acid, acetic anhydride and sodium nitrite generates the nitroso amide 359, which decomposes to 4-bromostyrene in the presence of rhodium(II) acetate. The procedure is thus a mild, non-basic alternative to the classical Hofmann elimination of amines396,397. 

Terminal olefins appear to be reactive only if they are not allylic in nature (e.g., styrene and 2,4,4-trimethyl-l-pentene). Allylbenzene (3-phenyl-l-pro-pene) is inert toward nitrosyl chloride, whereas propenylbenzene (1-phenyl-l-propene) reacts. The preparations are usually carried out at low temperatures. When molecular weights of the products are determined at 5°C, they correspond to dimeric structures. At the melting point of naphthalene, the products are predominantly monomeric. This observation is reasonably general for nitroso compounds [69]. 

In a study of the addition of nitrosyl chloride or nitrosyl bromide to norbor-nene and norbomadiene, it was observed that (a) there was no structural rearrangement during the reaction, (b) a cis addition had taken place, (c) nucleophilic solvents such as ethanol or acetic acid were not incorporated in the products. These facts seem to speak against an ionic addition mechanism, while a free radical initiated by NO radicals was considered unlikely since nitric oxide is inactive toward norbomadiene. Therefore a four-center mechanism has been suggested [70], However, when a relatively simple, unstrained olefin such as A9-octalin was subjected to the reaction, only blue, crystalline, monomeric 9-nitroso-10-chlorodecalin was produced. This product had a trans configuration. Thus it is evident that the structure of the olefin has a significant bearing on the steric course of the addition [71]. 

There are three possible products when NOCI is added to olefins.666 The initial product is always the p-halo nitroso compound, but these are stable only if the carbon bearing the nitrogen has no hydrogen. If it has, the nitroso compound tautomerizes to the oxime ... 

With some olefins, the initial p-halo nitroso compound is oxidized by the NOCI to a p-halo nitro compound.667 Many functional groups can be present without interference, e.g., COOH, COOR, CN, OR. The mechanism in most cases is probably simple electrophilic addition, and the addition is usually anti, though syn addition has been reported in some cases.668 Markovnikov s rule is followed, the positive NO going to the carbon that has more hydrogens. 

Aziridines not substituted on the nitrogen atom react with nitrous acid to produce olefins.324 An N-nitroso compound is an intermediate (2-51) other reagents that produce such intermediates also give olefins. The reaction is stereospecific cis aziridines give cis olefins and trans aziridines give trans olefins.325 Aziridines carrying N-alkyl substituents can be converted to olefins by treatment with ferrous iodide326 or with m-chloroperbenzoic acid.327 An N-oxide intermediate (9-28) is presumably involved in the latter case. 

Full papers have appeared on the formation and reactivity of the compounds ML(CNR)2 (M = Ni, Pd, Pt L = Oz, azobenzene, olefin, diazo-fluorene, acetylene) (231-237) (see also Sections IV,D,2 and V,D). Complexes of the type Ni(olefin)(CNBu )2 have been prepared for a large range of olefins (234, 237). The isocyanide stretching frequencies have been measured and related to the electron-withdrawing properties of the olefin. Other unsaturated molecules such as imines, diazenes, ketones, nitroso compounds, and acetylenes have been similarly studied. The effect of substituent change has been found to be cumulative and an empirical relationship has been developed to predict v(NC) (237). 

The interaction of aryldiazonium tetrachlorocuprates [Cu(II)] with olefins has been studied by ESR spectroscopy using the spin-trapping technique (Lyakhovich et al. 1991). The radicals ArCH2CH( )Ph and ArCH2CH( )CN have been detected in mixtures of the aryldiazonium tetrachlorocuprates [Cu(II)] with styrene and acrylonitrile using nitroso-durene as a spin adduct. However, aryl radical signals were not detected under those conditions. Obviously, aryl radicals react with the nearby ethylenic bond within the activated... 

The reaction of nitroalkanes and dinitroalkanes with sodium hydrogen telluride gives nitrosoalkane dimers and olefins, respectively.96 The reduction of other nitrogenated species such as hydroxylamines, azides, nitroso, azo, and azoxy compounds can also be performed by using tellurium reagents.6,11,12... 

The hetero Diels-Alder reaction of nitrosoalkenes with electron-rich olefins has been known for a long time [363]. A detailed mechanistic study carried out by Reissig et al. has given evidence that this inverse electron demand cycloaddition is a concerted process [364]. Recent ab initio calculations dealing with the reaction between ethylene and nitroso ethylene strongly corrobate this view [365]. In this work, Jursic and Zdravkovski have also investigated the influence of BH3 as Lewis acid catalyst. However, cycloadditions of nitrosoalkenes already pro-... 

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