3.4- fused indole skeleton synthesis

A Rh(III)-catalyzed intramolecular redox-neutral or oxidative cyclization strategy for the rapid synthesis of 3,4-fused indole skeletons from tethered alkynes was... 

Since then, numbers of catalytic systems were developed. Regarding the intramolecular cyclization, in 2004, Nishida and co-workers reported a new type of palladium-catalyzed cyclization, which proceeds via selective isomerization of a double bond in the enamine structure followed by 5-endo cyclization. Various fused indoles were produced in good yields (Scheme 2.110). Interestingly, this procedure was also applied for the synthesis of the azocinoindole skeleton. 

Since CHEC-I appeared in 1984, several reviews on specific fused (5,5,6) heterocycles have been published. A review on pyrrolo[l,2-a]indoles has appeared in which the different synthetic approaches leading to this particular heterocyclic assembly have been systematized <86RTC199>. Special interest of the authors in the five most important strategies leading to the pyrrolo[l,2-ajindole skeleton has been shown, of which the greater part is related to the synthesis of the mitomycins, alkaloid-type antibiotics with antitumor activity. The literature cited covered the period from 1978 to the end of 1985. 

Many reactions in heterocyclic multistep syntheses involve thermal condensations. Among these, the Niementowski reaction is the most common method for synthesis of the 31-f-quinazolin-4-one ring. It involves the fusion of anthranilic acid (or a derivative, e.g. 2-aminobenzonitrile) vith formamides or thioamides (or their S-methyl derivatives) and usually needs high temperatures and requires lengthy and tedious conditions. Recently, Besson and coworkers studied the possibilities offered by this reaction and explored the preparation of novel bioactive heterocycles (e.g. 38, 39, and 40 in Scheme 9.11) in which the quinazoline skeleton is fused with thiazole, indole or benzimidazole rings [50a-c]. 

An efficient three-component domino strategy for the synthesis of multi-functionahzed tetracyclic indeno[l,2-h]indole derivatives has again been reported by Tu, li, and coworkers [62]. The domino reaction between enaminones 57 and 2,2-dihydroxyindene-l,3-dione 105 in acid anhydride generated the fused pyrazoles 106 (tetracyclic 6-5-S-6 skeleton), which involved a nucleophilic substitu-tion/cychzation/methyl migration/aromatization/esterification. On the other hand,... 

---