Phenyl group, introduction into system

Introduction of a phenyl group into the 6-position of thieno- or pyrrolo[c[-tropylium ions (e.g., transition from 228 to 230) shifts the 5- and 7-methyl protons to high field (0.4 ppm) consequently, noncoplanarity of the 6-phenyl ring and heterocyclotropylium system must be concluded (68-ZOR907). 

As revealed by a comparison of the chromatographic behavior of 1 and 5 in Fig. 3-101, the introduction of a phenyl group into the molecule results in an increase in the retention at an identical number of phosphonic acid groups. This finding is explained by ji-ji interactions between the stationary phase and the aromatic ring system of the analyte. 

The silylenol ether formed from (47) and trimethylchlorosilane was cyclized in situ, and the reaction mixture was worked up under acidic conditions to give the ketone (558). This was subjected to reduction with sodium borohydride, acid-catalyzed elimination of water, and oxidation with dichlorodicyanobenzoquinone (DDQ) to give the bicyclic ester (560). Introduction of a methoxy substituent into the retinoid structure (560) was likewise effected via the ketone (558). When this ketone was ketalized with methyl o-formate, methanol was eliminated and the product was oxidized, its six-membered ring system undergoing aromatization to form a substituted phenyl group. 

Benzyne generated in situ by diazotization of anthranilic acid adds readily to aminides 172 to provide cycloadducts 171. Introduction of a nitro group into para position of the phenyl ring on the nitrogen terminus of the 1,3-dipole (X2 = N02) stabilizes the system and results in higher yields of product 171 (70% vs. 50% forX2 = H). Electron-deficient imines react also with aminides 172, but the yields of isolated adducts 173 are relatively low (10-26%) (Scheme 19) <2003ARK(vii)110>. 

The progressive introduction of methyl groups into the pendant phenyl ring of Cl Acid Blue 25 (6.30 R = H) leads to an increase in dye uptake and to improved wet fastness properties on wool [12]. Steric crowding in the case of Cl Acid Blue 129 (6.33) reduces the conjugation of the 4-substituent with the remainder of the system and results in a reddish blue hue. The aliphatic cyclohexyl ring in Cl Acid Blue 62 (6.31) has a similar effect on the hue. 

Recently it was shown that introduction of fluorescent groups into ionophoric calix[4]arenes provides new systems for recognition of alkali metal ions.<59 62) Because of the mobility of the phenyl units, conformational changes can be induced by solvents and metal ions. Examples are given in Figure 2.15. 

The slight but reproducible diamagnetic shift of H-2 (0.12 ppm) on introduction of the methoxyl group ( + M, —I) in the remote p-position of the phenyl substituents (Nos. 1 and 2) has been interpreted on the basis of the limiting structures 336 and 337. A pd conjugation179 must be taken into account in a detailed quantum mechanical treatment of the 1,3-dithiolium system.180... 

Tetrazolol 1,5-6Ibenzothiazoles generally exist in the tetrazole form in the solid state, but in CHC1, solution the azido form is also present.491 Introduction of electron-withdrawing substituents, such as N02 or Cl, in the phenyl ring results in a preference for the azide form, e.g., 236 (Scheme 27).488,491 Conversion of the sulfur atom of benzothiazoles into an S02 group as in compounds 237492 and 238493 completely favors the azide form, and the system is comparable to acyclic sulfonyl-substituted... 

---