Heteroaromatic groups

When the aromatic group of the sulfoxide is replaced by a heteroaromatic group (e.g., N-methylimidazole), the internal coordination between Li—N to form a five-membered metallocycle apparently predominates over Li—O coordination to form a four-membered metallocycle . Reaction of imidazole (S)-sulfoxide 16 with benzaldehyde produces aldol 17 as the major product in which the a-H and the sulfoxide lone pair are syn (equation 14) imidazole (R)-sulfoxide 18 reacts similarly (equation 15). The stereochemical outcome of these reactions is rationalized in terms of a-lithiosulfoxides in which the reactive diastereomer (i.e., 20 and 21) is that having one diastereotopic face of the five-membered Li—N metallocycle carrying both H and sulfoxide lone pair. 

The absorption and emission of radiation in the near ultraviolet (UV) and visible regions of the electromagnetic spectrum are associated with electronic (and associated vibronic) transitions involving n- and/or n-electron systems of molecules. Synthetic and natural polymers absorb in the UV region and particularly strong absorption spectra are recorded for polymers containing aromatic and heteroaromatic groups (e.g., poly(styrenes), poly(vinyl naphthalenes), poly(vinyl carbazoles)). 

Introduction of a heteroaromatic group in the spacer proved beneficial in the work by Johnson Johnson researchers Arts et al. [83] and Angibaud et al. [84]. Optimization of the initial lead, having a 1,4-substituted phenyl present in the spacer region (Fig. 15, entry 1), was done by replacing this R... 

Fig. 16 Introduction of heteroaromatic groups in the capping region of hydroxamic acid containing HDAC inhibitors. (Abbott Laboratories)...

In terms of chemical stracture, j3-adrenoblockers have much in common. Practically, all of them are derivatives of l-aryloxy-3-aminopropanol-2, the Cj position of which always possesses a substituted or nonsubstituted aromatic or heteroaromatic group connected by an ether bond to a three-carbon chain. An R group at the nitrogen atom of the propanoic region must be represented as either a tertiary butyl group (nadolol, timolol), or an iso-propyl group (the remainder of the drugs). 

Photoisomerization of E-C=C double bonds substituted with heteroaromatic groups that allow intramolecular hydrogen bonding were found to afford one-way E - Z... 

Mamaev, V. P., Shkurko, O. P., Baram, S. G., Electron Effects of Heteroaromatic and Substituted Heteroaromatic Groups,... 

Electronic effects of heteroaromatic and substituted heteroaromatic groups,... 

Fig. 25 Information storage in dihydroazulene/vinylhepta-fulvene systems attached to heteroaromatic groups.

Figure 3.19. Representative examples of 2H- -benzopyrans annellated with heteroaromatic groups on the f-face.

When the annellated heteroaromatic group is a five-member ring (43, 44), the properties are best described as intermediate between a naphtho and benzopyran. The standard method of synthesis for diaryl naphthopyrans (acid-catalyzed condensation between a diaryl propargyl alcohol and a naphthol, Scheme 8) is reported not to work for heteroaromatic fused phenols. This is true especially in cases where the heteroaromatic phenol contains a (basic) nitrogen. Alternatively, these pyrans can be prepared by the method of Casiraghi69 outlined in Scheme 16. 

Kumar70 has prepared a series of 2//-1-benzopyrans with heteroaromatic groups annellated on the f, g, or h face. These compounds have enhanced optical density due to the phenyls at the 2-position being ortho substituted, an effect much like that observed in the 3,3-diaryl-3//- naphthol2,1 6]pyrans as shown in Section 2.2.2. It is interesting that the colored forms of many of these compounds have very broad, double-humped absorptions. An example of the visible spectrum of a representative compound is shown in Figure 3.20. 

Heterocyclic variations on the basic stilbene — phenanthrcne theme are provided by many systems in which one or both of the phenyl groups of stilbene is replaced by a heteroaromatic group, or in which there is a pair of phenyl groups on adjacent positions in a heterocyclic ring. An example of the latter is seen in 1,2,6-triphenylpyridinium salts, which undergo photochemical cyclization to give a bridgehead aza-derivative of triphenylene (3.67). 

However, systematic studies by Katritzky et al. [3] have demonstrated that reactions of 1-substituted benzotriazoles with organomagnesium compounds constitute a versatile method for substitution a to a variety of functional groups, as exemplified in Scheme 8.1. It is noteworthy that the benzotriazolyl group is displaced in preference to alkoxy (contrast the reactions of aminals noted in Section 8.2.1) and other heteroaromatic groups such as carbazolyl. The following procedure is typical. 

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