Aza-polycyclic compound

Superacid-catalysed intramolecular reactions of some dicationic electrophiles have been investigated.36 The positively charged centres migrate apart and this chemistry gives a new synthetic route to aza-polycyclic compounds. The polycyclic compound (26) can, for example, be formed from reaction of 2-phenyl-3-(l-hydroxy-2-phenyl-ethyl)quinoline (25) with CF3SO3H at 25 °C, loss of water and benzene being involved. Highly diastereoselective polycyclization of homo(polyprenyl)arenes [e.g. (27)... 

The majority of published work on aza-ylides concerns their applications in synthesis, and here we report a selection of contributions from this area. The Staudinger reaction is a popular route to aza-ylides and has been used to prepare a series of perfluoroalkyl-tagged aza-Wittig reagents, e.g., (68), which were generated in situ (Scheme 22), and utilised in the synthesis of 3//-quinazolidine-4-ones in a fluorous biphasic system. A method for the preparation of aza-polycyclic compounds derived from pyrrolidine, indolizidine and indole has... 

Current IUPAC and Chemical Abstracts nomenclature has been employed in this index with the former given preference. Substitutive nomenclature has been given preference over radicofunc-tional, additive, subtractive, conjunctive or replacement nomenclature, except where this becomes unwieldy. With many bicyclic and polycyclic compounds bearing heteroatoms, standard bicyclic or polycyclic oxa, aza, and thia replacement nomenclature has often been used. With certain functional groups, where the names are rather complex and probably not familiar to most organic chemists, such as ylides, those compounds have simply been named as sulfur, tellurium and arsonic ylides. Metal catbenes have been treated similarly. With more complex functionality and many heterocycles, the Beilstein Commander Crossfire nomenclature system has been used with certain modifications. 

Superacid-promoted dicationic species containing heteroaromatic rings, where positive charge centres migrate through consecutive deprotonation-reprotonation steps, undergo cyclization reactions followed by aromatization and superacid-promoted elimination of benzene (Scheme 10).31 The process leads to the synthesis of aza-polycyclic aromatic compounds in moderate to good yields. Seven examples include pirazole, oxazole, and thiazole heterocycles. 

Scheme 3. Proposed mechanism for aza-polycyclic aromatic compound formation.

Thus, the diaddition reaction of bifunctional nucleophiles to alkyl-1,4-diazinium salts followed by the oxidation of cycloadducts formed provides us with a simple and effective route to preparation of polycyclic aza-aromatic compounds. 

Meta-cyclizations are often called meta-bridging reactions, since they yield polycyclic meta-bridged structures (74ACR181). In the series of aza-aromatic compounds, these reactions are mostly found with 3-nitro-substituted azines or with 1,3-diazines, as illustrated by Scheme 54 (77JOC2589). 

Very recently, chiral tricarbonylchromium complexes have been introduced as novel chiral auxiliaries for aza Diels-Alder reactions [192, 193]. Using the brominated imine 3-8, Kiindig s group was successful in efficiently generating enantiopure polycyclic compounds such as 3-10 by cycloaddition of 3-8 to l-methoxy-3-trimethylsilyloxy-l,3-butadiene (Danishefsky s diene), subsequent radical cyclisation of the cycloadduct 3-9 and oxidative metal removal from 3-11 (Fig. 3-3). 

Biological activation of polycyclic-hydrocarbon carcinogens proceeds through dihydrodiols and diol epoxides and such pathways are clearly possible for aza-aromatic compounds. To assist in investigating the existence of such routes, a range of dihydrodiols and diol epoxides of benz[c]acridine and benz[a]acridine (R.E. Lehr and S. Kumar, J. org. Chem., 1981, 367 ... 

Padwa and co-workers also explored the rhodium-catalyzed reaction of diazo imides to form isomunchnones. Subsequent in situ trapping affords aza-substituted polycyclic compounds. Thus 405 smoothly forms isomunchnones 406, which can be intercepted in high yield with DMAD to give furans 407, following loss of methyl isocyanate from the cycloadducts (Fig. 4.129). Likewise, the bicyclic... 

Also, synthesis of aza-polycyclic aromatic compounds such as novel phenazines and quinoxalines using TSA was reported by Karami et al. (2011) (Scheme 3.7). This stimulated our interest in further studies on the chemistry of catalysts. 

For example, as illustrated in Scheme 3.22, dibenzo[f,h]pyrido[2,3-b]quinoxa-line was prepared in refluxing ethanol as a novel aza-heterocyclic compound. This approach shows an interesting synthesis of the new polycyclic aromatic heterocycles, which was the main purpose of this work (Scheme 3.22). 

Karami, B., Khodabakhshi, S. and Nikrooz, M. 2011. Synthesis of aza-polycychc compounds Novel phenazines and quinoxalines using molybdate sulfuric acid (MSA). Polycycl. Aromat. Compd 31(2) 97-109. 

Other reactions that have been applied in the Ugi postmodification strategy are the aza-Wittig reaction [80-84] and copper-catalyzed processes [85, 86], More recently, Domling and coworkers have developed a new approach for the synthesis of polycyclic compounds via Ugi MCR followed by a Pictet-Spengler reaction [87-89]. In 2011, apro-tocol for the rapid access to quinolin-2-(l//)-one scaffold was reported by a sequential 4-component Ugi-Knoevenagel condensation [90]. Hulme et al. have introduced a one-pot, two-step protocol for large-scale production of libraries of novel peptidomimetic-like fcM-pyrrolidinone tetrazoles via the Ugi-3CR-azide reaction of tethered keto ester methyl... 

The gas-phase reactivity of pyridine radical cation was studied and it was shown to combine with molecules of acetylene to provide aza-polycyclic aromatic structures, such as the quinolizium cation. Similar processes were demonstrated for the radical cation of pyrimidine. It is suggested that similar chemical processes are involved in formation of aza-polycyclic aromatic compounds in interstellar clouds and solar nebula. 

Various polycyclic aromatic hydrocarbons, carbonyl arenas, polycyclic nitro-aromatics, aza arenes, N-nitroso compounds, and other carcinogens have been detected in ambient air (Hughes et al, 1980 Kneip et al, 1983 Spiegelhalder and Preussman, 1983). Diesel exhaust particles... 

The 1-ADPM rearrangement of 1-aza- 1,4-dienes affords the corresponding cyclopropylimines regioselectively. However, in order to predict the outcome of the reaction in pyrazinobarrelenes, quinoxalinobarrelenes, and other polycyclic systems, two different factors should be taken into account. One is the possible competition between the DPM and the 1-ADPM rearrangements, and the other is the influence of substitution on the stability of the reaction intermediates. However, in most of the cases studied, the 1-ADPM process takes place preferentially over the DPM reaction [3e]. An example of competition between these two reactions is shown in Sch. 4 for compound 5a [10a]. 

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