Diazatriphenylenes and their thiophene analogues: synthesis and applications

This review highlights the recent advances in the field of the synthesis of diazatriphenylenes and their structural analogues, such as phenanthrenes, fused with the thiophene ring, and naphthalenes, condensed with two thiophene rings. Also applications of these compounds are considered.


Scheme 3. Synthesis of the parent dibenzo[f,h]cinnoline (I).
Cobalt-mediated [2+2+2] cycloisomerisation of ynedinitriles 13-15, developed by Chercheja et al, 57 appears to be a novel, facile, and straight forward synthesis of dibenzo[f,h]cinnolines 16-18 (Scheme 4).In fact, the diazotization / Pschorr type ring closure of 30 is certainly a superior method for the preparation of 27, affording the target product in 70% yield (56% overall yield from 25) within 3 hours of the reaction time.It should be compared with 56% yield of the same product (49% overall yield from 25) reached for 64 hours of the intramolecular Pd-catalyzed arylation.

Intramolecular version of nucleophilic aromatic substitution of hydrogen (the S N
H reaction) has been used (59), by using concentrated sulfuric acid as a catalyst and iron(III) chloride, as an oxidant (Scheme 15). 79For a better understanding of the S N H reactions, see the recently published review 87 and references cited therein.Also oxidative cyclodehydrogenation (the Scholl reaction) appears to be a versatile tool for the construction of 1,3-diaza-analogues of triphenylenes.It requires a Lewis acid and oxidant, and is supposed to proceed through either the radical-cation (electron transfer) or arenium cation (proton transfer) intermediates. 88,89A variety of oxidants, including Fe(III), I(III), Tl (III), Ru(IV) and V(V), and their effects on the oxidative cyclodehydrogenation reaction, have been elucidated. 85In particular, Olivera et al. 85,90 have observed that phenyliodine(III) bis(trifluoroacetate) (PIFA) is the most suitable oxidant for the intramolecular reaction of non-halogenated 4,5-diarylpyrimidines (61) into the corresponding methoxy substituted dibenzo[f,h]quinazolines (62) in 23-88% yields (Scheme 16).Scheme 16.Synthesis of substituted dibenzo[f,h]quinazolines (62) via the oxidative cyclodehydrogenation of 4,5-diphenylpyrimidines (61).
Recently, Mohamed et al. 97 have proposed a novel versatile method for the synthesis of fused functionalized helicenes, affording, for instance, naphtho [

Conclusions
In this review article we have tried to present up-to-date literature data on the latest achievements in the chemistry of 1,2-, 1,3-and 1,4-diaza-analogues of triphenylene, phenanthro [9,10-b]thiophene and naphthothiophenes.In order to prepare 1,2-and 1,4-diaza derivatives of these polycyclic aromatic systems various types of condensation reactions appear to be appropriate ones, while the synthesis of 1,3-diaza compounds is usually realized via intramolecular cross-coupling reactions.It should be noted that from 32 possible diazaanalogues of triphenylene, phenanthro [9,10-b]thiophene and naphthothiophenes only 11 structures have so far been described in the literature.We believe that this review will be useful for organic chemists working in the field of polycyclic (hetero)aromatics and their metal complexes.

Acknowledgements
The research was financially supported by the Russian Science Foundation (Project No. 16-13-10435) and the Russian Foundation for Basic Research (research project №. 17-03-00011-А).

Figure 2 .
Figure 2. Structures of possible tetracyclic diazatriphenylenes and related thiophene-containing systems bearing the pyridazine ring.

Scheme 10 .
Scheme 10.Examples of biologically active compounds in the series of dibenzo[f,h]cinnolines (I).