Nitroso compounds cyclization reactions

On transforming the cyclopentenone 1431 into the trimethylsilyloxy diene 1432 the ensuing Diels-Alder cyclization gives rise to 69% tricychc compound 1433 [10] (Scheme 9.8). For Diels-Alder-reactions of thioaldehydes, selenoaldehydes, or unsaturated nitroso compounds with cyclopentadiene, see the reactions of 602 to 603 and of 605 to 606 in Scheme 5.48 and of 1092 to 1093 in Scheme 7.43. For Diels-Alder-reactions of silyloxyazadienes such as 510 with maleic anhydride to give 511, see Scheme 5.29. 

A related reaction accompanied by cyclization occurred with ortho-substituted benzamides (and also non-cyclic amides such as RCH(CONH2)2 [60]. Several compounds with a primary amino group, such as t-butylamine, p-tol uenesulphona-mide, ethyl carbamate, etc. were oxidized by DIB in presence of alkenes or nitroso compounds to give, respectively, aziridines or azoxy compounds. 

The acid-catalyzed cyclization to benzimidazole AT-oxides may also be conducted photolytically with good results.40 Denitration is not observed here and very clean reaction products are obtained. In a few cases, however, the corresponding benzimidazole and not its A-oxide is the sole product. Since these A-oxides are photostable under the reaction conditions, it appears that a different mechanism operates for the photocyclization. A plausible alternative (101)-(88) may be visualized by analogy to the photolytic rearrangement of o-nitro to o-nitroso compounds.43 The o-nitroso-A-oxide (110) may... 

Treatment of the ureide 129 or its 4-methyl derivative with diazomethane results in the formation of the monomethylated, and then the dimethylated spirohydantoin 131. This also demonstrates the ease of cyclization of these ureido derivatives. Similar reactions occur with 1,2-dihydro-2-oxo-3-ureidopyrido[2,3-h]pyrazine. If the methylated hydantoin 131 is treated with nitrous acid, the 1-nitroso compound 132 is formed. On alkaline hydrolysis this yields the 2-methylamino compound 133. The corresponding reactions with the 2-oxo isomer of 131 failed as... 

Oxadiazinan-2-ones 300 are obtained from norephedrine in good yield via N-alkylation, nitrosation, reduction, and cyclization <2002JHC823, 1996JME3938>. The nitroso compounds 299 are reduced with lithium aluminium hydride and the intermediate hydrazine alcohols cyclized with carbonyldiimidazole to afford compounds 300 (Scheme 37). Similarly, l,3,4-oxadiazinan-2-one derivatives 302 are obtained by reaction of hydrazino alcohols 301 with diethylcarbonate and sodium hydride (Equation 50) <2004SC835>. 

In 1962, Prof. John I. G. Cadogan at University of St. Andrews observed that aromatic C-nitroso compounds were readily deoxygenated by triethyl phosphite. Carbazoles were prepared from 2-nitrosdb ary s in this fashion albeit in low yields. Later on that year, he published an article titled Reduction of Nitro Compounds by Triethyl Phosphite A New Cyclization Reaction in the journal Proceedings of the Chemical Society In the paper, Cadogan described that 2- /7robiaryIs were also readily deoxygenated by... 

Because the nucleophiles can be introduced at the ortho-position of the nitro group, various heterocycles can be prepared via VNS and related reactions. Indoles and related compounds are prepared via the VNS reaction and subsequent cyclization. The VNS reaction of nitroarenes followed by cyclization with Et3N-Me3SiCl gives 1-hydroxyindoles (Eq. 9.53).86 Cyclization is also catalyzed on treatment with bases, in which nitroso intermediates are postulated. 

Coverage in this chapter is restricted to the use of alkenes or alkynes as enophiles (equation 1 X = Y = C) and to the use of ene components in which a hydrogen is transferred. Coverage in Sections 1.2 and 1.3 is restricted to ene components in which all three heavy atoms are carbon (equation 1 Z = C). Thermal intramolecular ene reactions of enols (equation 1 Z = O) with unactivated alkenes are presented in Section 1.4. Metallo-ene reactions are covered in the following chapter. Use of carbonyl compounds as enophiles, which can be considered as a subset of the Prins reaction, is covered in depth in Volume 2, Chtqiter 2.1. Addition of enophiles to vinylsilanes and allylsilanes is covered in Volume 2, Chapter 2.2, while addition of enophiles to enol ethers is covered in Volume 2, Chapters 2.3-2.S. Addition of imines and iminium compounds to alkenes is presented in Volume 2, Part 4. Use of alkenes, aldehydes and acetals as initiators for polyene cyclizations is covered in Volume 3, Chapter 1.9. Coverage of singlet oxygen, azo, nitroso, S=N, S=0, Se=N or Se=0 enophiles are excluded since these reactions do not result in the formation of a carbon-carbon bond. 

A side-chain methylenamino group reacts with a nitroso group (introduced in situ) when the compound is heated with mineral acid [2466]. An unusual reaction occurred when the nitro-t-amine (103.4) was refluxed with acetic anhydride and zinc chloride the course of this reaction may involve an A -oxide [2039]. When an o-nitroalkylamine is heated with ethoxide, the two functions are converted into a 1-hydroxyimidazole ring [3004]. Nitrosation of the pyrim-idinone (103.5) involves several steps including a Fischer-Hepp rearrangement of an iV-nitroso to a ring-C-nitroso the final product is a 6-(4 -nitrophenyl-amino)purin-2-one [2667]. In a weakly basic medium, the nitroamine (103.6) is cyclized to either the benzimidazole (when R == H), or the benzimidazolone (when R H). 

The nucleophilic substitution of 4-chloro-5-nitropyrimidines by a-aminocarbonyl compounds, followed by cyclization and oxidation, is also a useful, and widely applicable, method for the synthesis of pteridines (in place of the 5-nitro substituent aryldiazenyl or nitroso moieties can also be used). This reaction is sometimes known as the Polonovski-Boon synthesis.130,131 The use of aminoacetaldehyde diethyl acetal gives 6,7-unsubstituted pteridines, whilst amino ketones, aminonitriles, and amino esters give 6-alkyl-, 6-amino-, and 6-oxopteridines, respectively. 

Neiman found that 2-azido-2 -nitrobiphenyl cyclizes readily to benzo[c]cinnoline-iV-oxide on photolysis or thermolysis. The intermolecular counterpart of this reaction now has been found to be equally facile in some cases. Heating a- or jS-naphthyl azide and p-nitroso-iV, -dimethylaniline at reflux in bromobenzene produces the azoxy compounds 40 and 41 in virtually quantitative yield (Np = naphthyl). 

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