Benzo units

Crowns containing two or more fused benzo units.105... 

Table 3.15. Crowns having a meta-benzo unit as part of the macroring...

Very high distribution ratios are obtained with ligands including one and two benzo units in the polyethylene chain, DCs = 45 and DCs = 56, respectively. This enhancement of distribution ratios is explained by a lesser extraction of sodium, linked to a better complementarity of these ligands with cesium (Table 4.6).46... 

Phthalocyanines that possess two types of substituents on different benzo units are termed nonuniformly substituted, or unsymmetrical, phthalocyanines. There are three possible substitution patterns (i) where one of the benzo units is substituted differently from the other three (AAAB) (ii) where adjacent benzo units possess the same substituents ( adjacent, or AABB) ... 

There are many examples of phthalocyanine derivatives, given the general designation azaphtha-locyanines, in which one (or two) of the carbons in each benzo unit is replaced by a nitrogen. The synthesis and properties of such macrocycles has been the subject of a detailed review.65 The physical properties of azaphthalocyanines differ from those of phthalocyanines. For example, they form hydrates readily, which complicates purification and they are protonated by, and soluble in, dilute acids. In addition, the Q-band in the UV/visible absorption spectrum is blue shifted relative to that of phthalocyanine.65 Importantly, the aza moiety can be quaternerized to give water-soluble or amphiphilic derivatives.66 Thus, the cyclotetramerization of symmetrical 2,3-dicyanopyrazines provides a route to isomerically pure 1,4,8,11,15,18,22,25-octaazaphthalocyanines. 

Tetraazaporphyrin (3) (or porphyrazine) differs from Pc only in the absence of the four benzo units. The Q-band absorption of tetraporphyrins is found at shorter wavelengths ( 600 nm)69 and they are less prone to oxidation, which is advantageous for their use in catalysis. The cyclo-tetramerization of maleonitrile by the Linstead method, usually initiated by magnesium alkoxide, is by far the most important route to tetraazaporphyrins (Table l).70 The preparation and properties of substituted maleonitriles have been reviewed.71... 

Phthalocyanines that contain four benzo units fused to the ring are termed naphthalocyanines. If the benzo units are fused to the 1,2,8,9(10,11),15,16(17,18),22,23(24,25)-positions, the parent compound is termed 1,2-naphthalocyanine alternatively, if fused to the 2,3,8,9,16,17,23,24-positions, it is called 2,3-naphthalocyanine (4). The linear benzoannulation of 2,3-napthalocya-nines results in a bathochromic shift of the Q-band in the absorption spectrum of lOOnrn as compared to phthalocyanine.36,69 In addition, their enhanced ability to generate singlet oxygen makes them candidates for photodynamic therapy. Most synthetic routes to 2,3-naphthalocyanines... 

TABLE 8.8. DIBENZOTRIAZA-CROWN MACROCYCLES WITH AZA GROUPS TWO ATOMS REMOVED FROM THE BENZO UNITS... 

The isomerization of the 2,3-benzo derivative at 80°C provided another pathway for isomerization. Here, various derivatives gave 2-1-2 dimers (or adducts with furan) of 3,4-benzobicyclo[3.2.0]cyclohepta-l(2),3-diene derivatives which apparently were formed via a homofulvene with a disrupted benzo unit which undergoes a 1,5-shift (or two 1,3-shifts) (Scheme 8.33). The stereochemistry depicted in the scheme was inferred from the stereochemistry of the dimers and the formation of the /iJ<9-methoxy homofulvene was as observed in the debenzo derivative above. 

Unlike the corresponding oxa-crowns, crown thiothers with fused benzo rings have seen relatively little work. Klar and coworkers [66] prepared the hexa-methoxy derivative of tribenzo-9S3 by a modified Adams-Ferretti reaction between l,2-dibromo-4,5-dimethoxybenzene with l,2-dimercapto-4,5-dimethoxybenzene (Table 4). A variant of this procedure also affords the corresponding 12S4 analogue with four fused benzo units [67]. 

Another p-modified derivative, p-benzo-fused 17b, which possesses an extended TT-structure, provided a mesophase with TATA Cl as a tetragonal columnar (Coltet) phase with a = 4.21 nm and c = 0.73 nm based on a tetrameric assembly (Z = 4.02 forp = 1) (Fig. 4.12a). The mesophase range of 17bCl -(TATA ) was 24-102 °C. On the other hand, anion-free 17b formed a mesophase (33-166 °C) based on a Coin phase (a = 4.15 nm and c = 0.42 nm) consisting of a self-assembled dimer unit. In contrast to the assembled mode of the Colh structure of 14c C1 -(TATA - ), the receptor unit in 17b Cl -(TATA )+ faces the center of the circular unit with anions arranged on the inside, presumably because of the positions of the alkyl chains at the fused-benzo units at the p-positions of the pyrrole [31e]. 

Compound 10 serves as a key intermediate towards any further functionalization of the center benzo unit. For example, BDT unit with alkoxy side chains (11) was prepared from dione 10 through the reduction with zinc dust in aqueous sodium hydroxide solution followed by the alkoxylation with alkyl bromide or alkyl toluene-sulfonate [12, 21]. The synthesis of alkylated BDT unit 13 was first reported by Ong et al. (Scheme 3.4c). In their approach, reacting... 

BDT isomers and related polymers have recently been developed by Mullen and co-workers [41,42]. Depending upon the geometrical arrangement of the thiophene units and the benzo unit in the fused... 

If additional benzo units are likewise ortho-insed to the above pentacyclic system, helical structures result which can be specified as hexa-,hepta- etc. -helicenes. Since the current rules lead to confusing variable peripheral numberings for individual members of that compound class, a new consistent numbering scheme has been proposed according to which numbering always starts at one end of the helix and proceeds sequentially to the other. 

A high dilution way to the 11-membered macrocycle 15 was suggested. It has been shown that two phenyl substituents of bis(phenylphosphino)benzo unit are... 

Membered tetraphosphine macrocycle 28 was obtained utilizing high dilution procedure as a mixture of two mutually intercoverted isomers (Scheme 12.11). As in the case of the analogous 11-membered compounds 15 only the CIS configuration of phenyl groups of the o-bis-(tert-phosphino)benzo unit is observed in the macrocycle and the substituents of the phosphorus atoms occupy pseudoequatorial positions. In one isomer all lone pairs of P-atoms pointed into the molecular cavity [47]. 

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