Nitro compounds reductive cyclizations

The aminothiophene derivative 2, which is produced by reduction of the corresponding nitro compound 1, cyclizes spontaneously to the thienodiazepinedione 3. An analogous reaction of 4 yields compound 5.307... 

Aminocinnamoyl compounds (accessible by reduction of the corresponding 2-nitro compounds) undergo cyclization to give quinoline derivatives thus, from 2-nitro-cinnamic aldehydes or -ketones quinoHnes 65 are obtained, while from 2-nitrocinnamic adds the products are 2-quinolones 66 ... 

Perhaps the most reliable method for the reductive cyclization of a nitro ester to a hydroxamic acid is that which involves treatment with sodium horohydride in the presence of palladium on charcoal. Although under these conditions aromatic nitro compounds are reduced to amines, o-nitro esters such as 53, in which the ester group is suitably oriented with respect to the nitro group, give good yields of cyclic hydroxamic acids (54). Coutts and his co-... 

Kraus has reported the synthesis of a tricyclic indole related to the pyrroloiminoquinone marine natural products (Scheme 10.9), in which an intramolecular SNAr and the reductive cyclization of a nitro aldehyde are involved as key steps.94 Related target compounds have been prepared by Joule and coworkers via a similar strategy.95... 

The reduction of aromatic nitro compounds to amino derivatives and cyclizations to various heterocyclic compounds are presented in Chapter 9. Recent advances are presented here. Reaction of 2-nitrobenzaldehyde with vinyl carbonyl compounds in the presence of 1,4-diazbi-cyclo[2.2.2]octane affords Baylis-Hillman products, the catalytic reduction of which results in direct cyclization to quinoline derivatives (Eq. 10.78).134... 

Cyclization, reductive, aromatic nitro compounds to heterocyclic compounds, 48,115... 

Nitro compounds, aromatic, reductive cyclization with triethyl phosphite, 48, 115... 

Reaction of the TMS-nitro compound 1496 and the indole carboxaldehyde 1497 with a catalytic amount of TBAF led to the desired alcohol 1498, which, on further treatment with TFAA, followed by elimination of the corresponding trifluoroacetate with DBU, afforded the frans-stilbene 1499. Reductive cyclization of 1499 under Cadogan-Sundberg conditions afforded the bisindole 1500. Finally, condensation of 1500 with (dimethylamino)acetaldehyde diethyl acetal led to tjipanazole D (359) in 71% yield (796) (Scheme 5.255). 

Tris[(2-perfluorohexyl)ethyl]tin hydride has three perfluorinated segments with ethylene spacers and it partitions primarily (> 98%) into the fluorous phase in a liquid-liquid extraction. This feature not only facilitates the purification of the product from the tin residue but also recovers toxic tin residue for further reuse. Stoichiometric reductive radical reactions with the fluorous tin hydride 3 have been previously reported and a catalytic procedure is also well established. The reduction of adamantyl bromide in BTF (benzotrifluoride) " using 1.2 equiv of the fluorous tin hydride and a catalytic amount of azobisisobutyronitrile (AIBN) was complete in 3 hr (Scheme 1). After the simple liquid-liquid extraction, adamantane was obtained in 90% yield in the organic layer and the fluorous tin bromide was separated from the fluorous phase. The recovered fluorous tin bromide was reduced and reused to give the same results. Phenylselenides, tertiary nitro compounds, and xanthates were also successfully reduced by the fluorous fin hydride. Standard radical additions and cyclizations can also be conducted as shown by the examples in Scheme 1. Hydrostannation reactions are also possible, and these are useful in the techniques of fluorous phase switching. Carbonylations are also possible. Rate constants for the reaction of the fluorous tin hydride with primary radicals and acyl radicals have been measured it is marginally more reactive than tributlytin hydrides. ... 

Nitro compounds can be cyclized to give quinolines in two non-reductive processes. In the first, an o-nitro-cinnamate or -cinnamonitrile is cyclized by treatment with cyanide ions, via the cyanide addition product as generalized in equation (29). The reaction has been... 

The requisite hydroxylamine function for such cyclizations can also be generated from a precursor having a nitro group. This novel route has provided access to hitherto unknown l-hydroxy-6-allyl-, and -6,6-bisallyl-piperazine-2,5-diones (91UP1). The starting material is an W-nitroacetyl amino acid ester that can be either mono-or bis-allylated at the methylene adjacent to the nitro group. Reduction of the N02 to NHOH using zinc/ ammonium chloride, followed by cyclization, leads to the desired products (Scheme 76). Compound (215) is unique in that it possesses a chiral center at C-3 and a quaternary carbon at C-6 on a l-hydroxypiperazine-2,5-dione system. 

Substituents on thiocoumarins behave in predictable fashion for example, 3-nitro compounds afford the 3-amines on reduction, while 3-acyl derivatives readily form normal carbonyl derivatives such as phenylhydrazones, or enoic acids with malonates. These derivatives may frequently be cyclized on to position 4 of a 4-hydroxythiocoumarin to give products such as (119) (equation 59). 

Aminobenzo[6]thiophene and its simple ring-substituted derivatives are most conveniently obtained by reduction of the corresponding nitro compound with tin and hydrochloric acid,883,334,544,545 iron and hydrochloric acid,555 ferrous sulfate and ammonia,185,330 333 334,497 sodium borohydride and palladized charcoal,337 cata-lytically,152, 422,488,543 or, preferably, with Raney nickel and hydrazine hydrate.152,298,338,497,556 Several 5-aminobenzo-[6]thiophenes may also be made by cyclization reactions (Section IV, D).239,330,331 333,494... 

The indolyl nitro compound (98) was converted to the corresponding nitrile oxide, which cyclized to afford an inseparable mixture of isoxazolidines (99) and (100 Scheme 2S).46 These were acetylated and the THP group replaced by a mesyl group at which point the desired 3-isomer could be separated. Elimination via a selenide intermediate provided the alkenylisoxazoline (101), which was converted to an isoxazolinium salt and reduced with LAH to give an N-methylisoxazolidine. Reductive cleavage with aluminum amalgam provided (+)-paliclavine. 

Nitrodienes undergo intermolecular Diels-Alder reactions with appropriate dienophiles. The resulting nitro compounds can then be cyclized via a nitrile oxide intermediate.49 Thus, the 2-chloroacrylonitrile Diels-Alder adduct of 8-nitro-l,3-octadiene was prepared and cyclized to give (105) as a 3 1 mixture of diastereomers (Scheme 30). The Diels-Alder adduct of dimethyl acetylenedicarboxylate and 8-nitro-l,3-octadiene cyclized exclusively at the conjugated double bond, activated by the ester groups. Similarly, the quinone Diels-Alder adduct (106) cyclized at the conjugated double bond reduction of the conjugated double bond permitted cyclization on the cycloalkenyl double bond. 

Azole approach. Application of the commonly used method for reductive cyclization of aromatic nitro compounds by means of triethyl phosphite to the 4-c-nitrobenzylidene oxazoles (249) leads to the fused quinolines (250) (69JCS(C)385). 

From or via o-substituted cinnamoyl derivatives. or/ -Substituted benzenes of type 93 (Z = 0, S, NH) can undergo ring closure (Scheme 61). Amines of type 93 (Z = NH), which usually cyclize spontaneously, are often prepared in situ by reduction of nitro compounds, e.g., o-nitrocinnamic acid with (NH4)2S gives 2-quinolone. 

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