Benzo-fused carbocycles

Other benzo-fused carbocycles could be prepared in moderate yield by a similar strategy. Isomerically pure 3-substituted benzocyclobutenes or 5-substituted tetralins, 211, were prepared by a five-step sequence from the appropriate a-(2-fluorophenyl)-[Pg.101]

As reactions in benzo-fused rings are generally similar to simple carbocyclic compounds, our discussion of these is limited. 

Several examples are known for coupling of triflyloxy derivatives in the carbocyclic part of benzo-fused azines. 8-Quinolyl triflate reacts in the same manner as aryl triflates (87JA5478 89AJC279). Another example is provided by the 6,8-difluoro-7-triflyloxyquinoline (142), which has been used in a coupling reaction with 3-tributylstannylcyclopent-2-enone to form (143) (90TL1837). 

The reactivity of substituents on the fused benzene rings of (benzo)pyridazine derivatives was not discussed in CHEC-I because it is little different from that of the corresponding fused carbocycles,... 

Studies on benzo-fused analogs of 78 have also been reported. Solutions of unstable dibenzo[b,e]phosphabenzene (phosphaanthracene) (80, R = H)286 and dibenzo[6,d]phosphabenzene (phosphaphenanthrene) (81)287 have been prepared and examined by UV spectroscopy. The overall shape of the spectrum due to 80 (R = H) resembles that of anthracene rather than acridine, whereas that of 81 resembles the phenanthridine more closely than the phenanthrene spectrum. The absorptions of both 80 (R = H) and 81 show the typical strong bathochromic shifts relative to their nitrogen and carbocyclic analogs. 10-Phenyldibenzo[6, e]phospha-benzene (80, R = Ph)288 is more stable than its parent and shows similar UV absorption. 

Reactivity of some thiocanes, tetrahydrothiocins, and benzo-fused analogues were reviewed in the first edition. For the most part, reactivity and chemistry of those rings systems are that which are expected from their carbocyclic counterparts, with few exceptions. 

The aryne C—C triple bond is highly reactive toward palladation processes, and the initially formed arylpalladium intermediate can undergo a variety of transformations with an appropriate reagent in an intermolecular, giving rise to 1,2-functionalized benzene derivatives, or in an intramolecular manner, leading to benzo-fused (hetero)carbocyclic systems. 

Three different fused systems have been reported in the literature thieno[3, 2 4,5]thieno[2,3-c]pyridine (f/r-thiophenes), thieno[2, 3 4,5]thieno[2,3-c]pyridine (tram- thiophenes) and thicno[3,2-g]thicno [3,2-d pyridine derivatives. So far, the parent thienothienopyridines have only been prepared via the corresponding pyrylium salts (see below) all others are benzo or extended carbocyclic derivatives, for example, thienothienoquinolines. 

It is a predictable consequence, therefore, that substituents at positions a and y to the ring nitrogen have an enhanced reactivity, whereas substituents /3 to ring nitrogen or in a fused benzo ring behave more as would be the case if they were attached to the equivalent benzenoid carbocyclic system. 

Volume 2 covers five-membered rings with one heteroatom together with their benzo- and other carbocyclic-fused derivatives. 

The following monocyclic, benzo-, and dibenzo-fused ring systems, including dihydro, and tetrahydro derivatives, are treated in this chapter. Further carbocyclic and heterocyclic condensed systems are also described. 

Several saturated parent systems shown in Scheme 1, especially (2), (4) and (7), have been incorporated into spiro compounds or have been fused with a variety of non-aromatic carbocyclic or heterocyclic rings. Unsaturated compounds with an endocyclic carbon-carbon double bond, formally possible in all systems with three adjacent heteroatoms, are only known in very few cases (e.g. cyclic sulfites and sulfates of enediols) or in the form of benzo or other condensed systems (mainly cyclic sulfites and sulfates of aromatic 1,2-dihydroxy compounds). For details concerning the various types of derivatives, see Section 4.33.4.2. 

Schatz J, Brendgen T, Schuhle D (2008) Five-membered rings with one heteroatom togethta-with their benzo and other carbocyclic-fused derivatives. In Katritzky AR, Ramsdtai CA, Scriven EFV, Taylor RJK (eds) Comprehensive heterocyclic chemistry III, vol 3. Oxford, Elsevier, Amsterdam, p 932... 

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