Fused tricyclic

Complexation with metals has been observed with a variety of pyridopyridazinones, whilst electrophilic attack at nitrogen is involved in cyclizations to a variety of azolo and azino fused tricyclic systems, e.g. (65CPB586, 7UOC3812). 

Fluorous Mixture Synthesis of Fused-Tricyclic Hydantoins. 114... 

Fig. 32 Fluorous mixture synthesis of fused-tricyclic hydantoins. Reagents and conditions a Mo(CO)6, DMSO, toluene, MW 150 °C, 35 min, closed system b TFA CH2CI2 (1 1), rt c PhC2H4NH2, PyBOP, i-Pr2EtN, MeOH, CH2CI2 followed by flash chromatography and F-HPLC d i-Pr2EtN, MeOH, MW 140 °C, 40 min, followed by F-SPE...

The susceptibility of phosphites to hydrolysis limits their application as ligands for homogeneous catalysis. The fused tricyclic monophosphites derived from ca 1 i x[4]arenes260-262 form coordination complexes with palladium.263... 

This process allowed, for example, formation of the angulary fused tricycle 1-13 containing a five-, six-, and eight-membered ring from precursor 1-12 in 64% yield (Scheme 1.4) [Id]. 

Very recently, the Alcaide group constructed fused tricyclic systems from mono-cyclic precursors by a novel and elegant domino mesylation/[3,3] sigmatropic rearrangement/Diels-Alder reaction [467]. This domino process will be described in Chapter 4. 

The [6.5.5]-ring fused tricyclic motif is found in many natural products, and has therefore become an important target in synthesis. A convenient access to this structural framework is offered by a radical domino procedure published by the Nagano group [41]. This reaction of optical pure dibromoacetal 3-85 led to the desired tricycle 3-87 via 3-86 as a single diastereoisomer in a very respectable yield of 94% by applying classical radical conditions (excess tributyltin hydride/AIBN, irradia-... 

Scheme 3.22. Domino radical cyclization procedure for the synthesis of [6.5.5] fused tricycle 3-87.

Recently, the Cuerva group also presented a titanocene-catalyzed domino cycliza-tion of an aryl epoxypolyene such as 3-151, which led to the formation of a trans/ anti/trans-fused tricyclic compound 3-152, though in only moderate yield. Nevertheless, six stereogenic centers are formed in this domino process [64]. 3-152 could be transformed into the natural terpenoid stypoldione (3-153) (Scheme 3.40) [65]. 

Scheme 6/3.11. Ru-catalyzed preparation of angulary fused tricycles...

Subsequent, investigation showed that with prolonged reaction times the initially formed cycloadduct 22a then underwent [2+4+]-polar cycloaddition followed by a sequence of rearrangements to afford a novel benzo-fused tricyclic compound 42 (see Equation 11) <1996CC2185>. Various experiments were conducted in order to elucidate the mechanism of the formation of 42. 

A general synthesis of dibenzo-annelated dithieno[3,Z-b Z, 3 - thiophene 18 has been reported from bis(o-hydro-xyl)diacetylenes. This cyclization constructs a fused tricyclic skeleton in one pot. The subsequent dechalconization with copper powder produces a series of thiophene and selenophene-based heterocenes (Scheme 64) <20050L5301>. 

Linear and angular thiazolothienopyridines have been synthesized from the thiazolopyridinethione 105, by reaction with bromoacetophenone 106 to give the linear product 107, or sulfur and triethylamine to give the angular fused tricycle 104 (Scheme 7) <2003JCCS1061>. 

Chukhadzyan et al. made N-junction fused tricyclic systems such as 123 via a base-catalyzed cyclization onto the tetrazole 122 (Equation 29). The exothermic reaction proceeds at room temperature <1999CHE343>. 

As with other diazines, addition of benzonitrile oxide to pyridazines results in the formation of angular-fused tricyclic products C1995T11855, 1996T6421>. 

The linear-fused tricycle 446 was a key intermediate in the synthesis of the marine toxin azaspiracid (Equation 121) <2004H(63)539, 2004TL351>. 

Ortho-Fused Tricyclic Heterocycles with No Ring-Junction Heteroatom 775... 

Ortho-Fused Tricyclic Heterocycles with Heteroatoms at the 5 5 Ring Junction 793... 

Ortho-Fused Tricyclic Heterocycles with Two or More Ring Junction Heteroatoms 821... 

A four-component Ugi reaction between the thienopyrrole-diketo-acid 280, an isonitrile and an amine gives the fused tricycle 281 with two nitrogens in the six-membered ring <2006SC903> (Equation 44). 

Pyrazolopyrazoloquinoline derivatives can be prepared by treatment of pyrazolidin-3-one with 2-chloroquinoline-3-carbaldehyde, which gives firstly the zwitterionic compound 283. Reduction with sodium borohydride followed by ring closure in basic media gives the fused tricyclic heterocycles (Scheme 77) <1991T9599>. 

Modified neglect of diatomic overlap (MNDO) calculations can support the structures assigned to certain of these fused tricyclic systems, such as 401, where confirmatory X-ray crystallographic data are lacking <1983JCM128>. 

Fused Tricyclic Heterocycles with a 5 6 Ring Junction Heteroatom 881... 

The enamine 141 can be cyclized to the [l,2,4]triazolopyridopyrimidine 142 upon treatment with sodium ethoxide (Scheme 40) <2002M1297>. This fused tricyclic system may also be obtained, like the pteridine analogue (cf. Scheme 38), from the reaction of hydrazonoyl halides and pyridopyrimidines such as 143, and also by treatment of the triazolopyrimidine 144 with dimethylformamide dimethylacetal (DMF-DMA) dimethylacetal and subsequent ring closure <2003MOL333, 2003HAC491> (Scheme 41). Another series of triazolopyridopyrimidines, for example, 146, can be prepared from a hydrazine-substituted pyridopyrimidine 145, in two ways either directly by reaction with an acid chloride, or via a derived hydrazone (Scheme 42) <1996MI585>. 

Coumarins and related ring systems may be converted into benzo-fused tricyclic heterocycles by the simple transformations shown in Equations (113)—(116) <2003JHC249>. 

The stereoselective synthesis of classical trinems (fused tricyclic systems having the azetidin-2-one nucleus fused through the N-C4 bond) <98MI347> and the chemistry of non-classical polycyclic P-lactams have been reviewed <00T5743>. 

It is worth noting that product 443 was not obtained without silicon assistance, which means that the reaction is in fact initiated by an Si-[Rh] species (Scheme 112). Fused tricyclic benzenes such as 443 are formed exclusively using an exactly stoichiometric amount of silane. On the other hand, 2 equiv. of silane preferably lead to the formation of silylated benzenes such as 447 through a hydrosilyIation-carbocyclization-/ -hydride elimination cascade process. 

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