Nitrosobenzene, cycloaddition

Neurotoxin, frog, 86 Nitriles, 146-150 intramolecular, 149-150 Nitrosobenzene, cycloaddition, 72-78 Nitrosyl cyanide, 87... 

IH-Azepine, 1-methoxy carbonyl-cycloaddition reactions, 7, 522 with nitrosobenzene, 7, 520 tricarbonyliron complex acylation, 7, 512-513 conformation, 7, 494 tricarbonylruthenium complex cycloaddition reactions, 7, 520 1 H-Azepine, l-methoxycarbonyl-6,7-dihydro-synthesis, 7, 507... 

The same diazepine acts as a 4 -component in the cycloaddition with nitrosobenzene to give the bridged compound 22.101... 

Ri = OH, OCH3 R2 = CgHs, 4-CH3C6H4, camphoryl Scheme 55 Cycloaddition with electrogenerated nitrosobenzenes. 

Diels-Alder and hetero [4 -I- 2] cycloadditions of l-(l,3-butadien-l-yl)benzotriazole (638) with N-phenylmaleimide, maleic anhydride, ethyl acrylate, Eschenmoser salt, and nitrosobenzene give a... 

Similarly, the formation of the pyrrolinone (4) from the reaction of nitrosobenzene and a-pyrone may also involve the 2H- 1,2-oxazine (3), which then traps a second molecule of the nitroso compound in a [4+2] cycloaddition step (Scheme 2) (76JOC2496). 

Cycloadditions of nitroso compounds and 1,3-dienes lead to 3,6-dihydro-2//- 1,2-oxazines this is a well tried and documented procedure (B-67MI22700), a comparatively modern example of which is the regiospecific synthesis of 2,3,4-trisubstituted derivatives (155) from the addition of nitrosobenzenes to 1,2-disubstituted dienes (154) (78T697). 

Diels-Alder reactions. The cycloaddition of nitrosobenzene with 1 has been used for synthesis of an amino sugar (4).1... 

The [4+2] cycloaddition of 2-substituted-l,2-dihydropyridines 109 with heterodienophile nitrosobenzene gives unstable cycloadducts 110 as single diastereomers in 98% ee. Adducts 110 can be reduced with alane to give 3-aminosubstituted-l,2,3,6-tetrahydropyridines 111 with a /razw-relationship between the 2-substituent and 3-amino group (Scheme 30) <2005JOC2368>. 

The Regioselectivity ofHetero Diels-Alder Reactions. In a few cases, carbonyl, nitrosyl, cyano, and other double bonds with one or more electronegative heteroatoms have acted as dienophiles in Diels-Alder reactions. The carbonyl group has a HOMO and a LUMO as shown in Fig. 1.51. The energies of both orbitals are relatively low, and most of their Diels-Alder reactions will therefore be guided by the interaction between the HOMO of the diene and the LUMO of the carbonyl compound. This explains the regioselectivity in the cycloaddition of dimethylbutadiene 6.176 and formaldehyde, and between 1-substitituted butadienes 6.177 and nitrosobenzenes. 

When l-trifluoromethyl-l,3-cyclohexadiene undergoes cycloaddition with nitrosobenzene, only one dihydro-1,2-oxazine 1 is regio- and stereoselectively obtained, in very good yield54. 

When acylnitroso derivatives are employed as dienophiles in the cycloaddition, the re-gioselectivity of the reaction is inverted with respect to the mode of addition of nitrosobenzene. Thus l,2-dihydro-A -methoxycarbonylpyridine. by reaction with V-acylhydroxylamines in the presence of tetraalkylammonium periodate at 78 r C in dichloromethane, leads to the corresponding 2-oxa-3,5-diazabicyclo[2.2.2]oct-7-enes in good yield. The regiochemistry of the cycloaddition product 2 was determined by 13C NMR84-86. 

Very recently, Pericas reported a new strategy to immobihze trans-4-hydroxypro-line onto an insoluble Merrifield-type polymer by exploiting Cu(I)-catalyzed 1,3-dipolar cycloaddition ( click chemistry ) [42]. The supported catalyst 25 was successfully employed in the a-aminoxylation of ketones and aldehydes (Scheme 8.13). Under the optimized reaction conditions (20mol%/cat, 2 equiv. ketone, DMF, 23 °C, 3 h), the reaction of cyclohexanone with nitrosobenzene catalyzed by 25 gave the product in 60% yield and 98% ee (Scheme 8.13 Equation a). It should be noted that the reaction rates of cyclic ketones with supported catalyst are faster than those reported with (S)-proline. The use of a supported catalyst allowed for a simplification of the work-up procedure, as the product could often be obtained after simple filtration of the catalyst and evaporation of the solvents. Furthermore, 25 was recycled up to three times without any decrease in either the chemical and/or stereochemical efficiency. 

A -Acyl-l,2-dihydropyridines undergo regioselective Diels-Alder cycloadditions with nitrosobenzene [Eq. (5)]. ... 

Cycloadditions of nitrosobenzenes with simple carbocyclic 1,3-dienes have been known for many years.Ib 4 In a recent investigation, Kresze et al. have added p-chloronitrosobenzene to some 5,6-difunctionalized 1,3-cyclohexadienes (Scheme 3-VI).15 In the first example shown, only one cycloadduct was produced, although it is not obvious why this is the case. Also puzzling is the stereochemical result of the second example shown in the scheme. Based on Hart s work (Scheme 3-IV), one might have expected the sy/i-hydroxyl isomer to be the major product of this reaction. 

The regiochemistry of the addition of a-chloronitroso compounds with unsymmetrical acyclic dienes has been probed, and some results are listed in Table 3-II.lb 3a 23 In general, orientational preferences are in accord with those observed for arylnitroso compounds (cf. Table 3-1). As noted above, a glaring exception is the case of isoprene, which gives the opposite selectivities with chloronitroso compounds and nitrosobenzene. It was suggested that steric factors become important in cycloadditions... 

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