Aromatics disubstituted

Chiral 10 to 12-membered nitrogen and oxygen heterocycles, fused to isoxazo-line rings have been prepared with high regio- and stereoselectivity by INOCs of tethered N- and O-allyl carbohydrate derivatives. The use of a -Y-Ar-CH2 tether, containing a 1,2-disubstituted aromatic ring between the heteroatom attached to... 

The UV spectrum [/Imax 245, 296, 341, 352 (sh), and 368 nm] of TAN-999 (296) was very similar to that of (+)-staurosporine (295), indicating the presence of a similar indolo[2,3-fl]carbazole framework with a lactam function. This was also discernible from its IR spectrum with the presence of an NH band at v ax 3430 cm and an amide band at 1680 cm . The H-NMR spectrum of TAN-999 was also very similar to that of (+)-staurosporine, except for the presence of an additional methoxy group at S 3.95, resulting in the presence of a 1,2,4-trisubstituted aromatic ring instead of a 1,2-disubstituted aromatic ring. The location of this additional methoxy group was assigned to C-10, based on COSY, COSY, refocused INEPT, and... 

Two different carbon functional groups can be introduced simultaneously into 1,2-positions of aromatic skeletons based on a novel insertion reaction of arynes (101) into a carbonyl-cyanomethyl a-bond of a-cyanocarbonyl compounds (102) to produce 1,2-disubstituted aromatics (103).134... 

The 1,4-dinucleophilic building blocks used most are 1,2-disubstituted ethanes of the type HXCHiCHjYH, semicarbazides, thiosemicarbazides, hydroxamic acid amides, amidrazones, and 1,2-disubstituted aromatic and heteroaromatic compounds. 1,1-Dielectrophilic building blocks preferentially used are perfluorinated carboxylic acids and their derivatives, such as acid halides, anhydrides, imidoesters, nitriles, perfluoroalkyl chlorosul-... 

Haworth reaction A reaction in which an aryl compound is treated with a cyclic anhydride, such as succinic anhydride, and the intermediate Friedel-Crafts product is reduced and then cyclised via an internal Friedel-Crafts reaction to give a 1,2-disubstituted aromatic compound with a carbonyl group in the new ring. The whole sequence is called the Haworth reaction. 

The mass spectra of radical anions of 1.2-disubstituted aromatic compounds sometimes contain signals which must be attributed to the operation of an ortho effect14,1S. Remarkably the spectra of the negative ions in some cases permit a... 

Conveniently prepared from phenols, more readily available than the corresponding aryl halides, and recognized as the most powerful in the hierarchy of DMGs [63], the aryl O-carbamates are primed for synthetic application. One application is their use in the regioselective preparation of polysubstituted aromatics and then involvement as leaving groups in subsequent Suzuki-Miyaura or Kumada-Corriu (Section 14.3.1.2) cross-coupling reactions for the establishment of 1,2-disubstituted aromatics, illustrated by the conceptual 1,2-dipole synthetic equivalent, 35 36 = 37 (Scheme 14.10 and Scheme 14.11) [64]. 

P=0 Stretching vibrations), and 751 cm (deformation vibration caused by the 1,2-disubstituted aromatic DOPO rings), while the phosphorus-free resin EP-0 spectrum presented characteristic bands only at 2,970 cm" and 2,930 cm" (aliphatic C-H asymmetric stretching vibrations), 2,875 cm" (aliphatic symmetric stretching vibration), 1,610 cm and 1,501 cm" (aromatic C=C stretching vibration), and at 1,240 cm" and 1,040 cm" (-C6H4-0-CH2-asymmetric and symmetric stretching vibrations, respectively). 

Because the position of electrophilic attack on an aromatic nng is controlled by the direct ing effects of substituents already present the preparation of disubstituted aromatic com pounds requires that careful thought be given to the order of introduction of the two groups Compare the independent preparations of m bromoacetophenone and p bromoace tophenone from benzene Both syntheses require a Friedel-Crafts acylation step and a bromination step but the major product is determined by the order m which the two steps are carried out When the meta directing acetyl group is introduced first the final product IS m bromoacetophenone... 

Because the position of electrophilic attack on an aromatic ring is controlled by the dir ecting effects of substituents aheady present, the preparation of disubstituted aromatic compounds requires that careful thought be given to the order of introduction of the two groups. 

Of particular synthetic importance is the coupling of aryl- and hetarylboronic acids to aryl- and hetaryl halides (or triflates), allowing for a convenient synthesis of biphenyls, even sterically demanding derivatives such as 14, hetaryl phenyls and Zj/ -hetaryls. With appropriately disubstituted aromatic substrates, the Suzuki coupling reaction can be applied in the synthesis of polyphenylene materials. 

Regarding the series of hetero aromatic pentacyclic compounds with three heteroatoms, an accelerated synthesis of 3,5-disubstituted 4-amino-1,2,4-triazoles 66 under microwave irradiation has been reported by thermic rearrangement of dihydro-1,2,4,5 tetrazine 65 (Scheme 22). This product was obtained by reaction of aromatic nitriles with hydrazine under microwave irradiation [53]. The main limitation of the method is that exclusively symmetrically 3,5-disubstituted (aromatic) triazoles can be obtained. 

An /n-geometry can be ensured by appropriate substitution of the building block which carries the acid-base functionality, for instance by using 2,6-disubstituted aromatic compounds like pyridines, 2,6-disubstituted benzoic acids or other 2,6-disubstituted phenyl derivatives (see Scheme 1). The use of 2,6-disubstituted arenes is sometimes called the 1,3-xylyl trick and assures an intra-annular orientation. 

Figure 2. Origin of the nonlinearity of charge-transfer molecules for a two-level-like disubstituted aromatic molecule. The donor (D) and acceptor (A) cooperate to distort the linear response (dotted lines) of a nonsubstituted benzene ring (below).

It has been found that the disproportionation of toluene over ZSM-5 catalyst can be directed such that p-xylene is the predominant xylene isomer (14-17). This reaction, designated STOP, is one of several in which disubstituted aromatics rich in the para isomer are produced. Others are the alkylation of toluene with methanol to produce p-xylene (15,18) and with ethylene to produce p-ethyltoluene (19,20), as well as the aromatization of olefins (20), paraffins (20) and of methanol... 

Commonly, ortho elimination refers to a hydrogen transfer via a six-membered transition state at ortto-disubstituted aromatic compounds. In practice, the reacting entities are almost in position to form this six-membered transition state. The general mechanism of the ortho elimination is as follows ... 

The conditions leading to the formation of F indicate a disubstituted aromatic ring. In addition, the reaction conditions and formula indicate thatFis a diccirboxylic acid. Disubstitution may be ortho, meta, or pcira. 

Much of the initial synthetically useful carbonyl ylide work originated from the Ibata group. Exploiting simple disubstituted aromatic diazoketo-esters and structurally diverse dipolarophiles, Ibata and co-workers (64—70) prepared several different cycloadducts 167-169 through an intermolecular ylide cycloaddition (Scheme 4.38). 

Box 3.4 Out-of-plane C-H Bending Vibration Frequencies of Mono- and Disubstituted Aromatic Rings... 

Many intramolecular nitrone cycloadditions have been carried out on substrates containing a cyclic intervening bridge. Perhaps the simplest possibility here is an o-disubstituted aromatic substrate, as, for example, the nitrone derived from aldehyde (42), which cyclizes to the 5,6-fused isoxazolidine (43 Scheme 10).19 There are many additional possibilities the nitrones derived from biphenyl aldehyde... 

Substituted aromatic compounds are named using the suffix -benzene. Thus, C6H5Br is bromobenzene, C6H5CH3 is methylbenzene (also called toluene), C6H5N02 is nitrobenzene, and so on. Disubstituted aromatic compounds are named using one of the prefixes ortho-, meta-, or para-. An ortho- or o-disubstituted benzene has its two substituents in a 1,2 relationship on the ring a meta- or m-disubstituted benzene has its two substituents in a 1,3 relationship and a para- or p-disubstituted benzene has its substituents in a 1,4 relationship. When the benzene ring itself is a substituent, the name phenyl (pronounced fen-nil) is used. 

The Relative Rates of Reaction of Disubstituted Aromatic Compounds... 

An alternative is FGI back to the ketone 67 and hence the a-bromoketone 68 that can be made from the ketone 69 itself by methods discussed earlier in this chapter. The ketone 69 is clearly made by some sort of Friedel-Crafts acylation, but how are we to make the diol 70 In chapter 3 we said that a good strategy to make ort/io-disubstituted aromatic compounds was to start with an... 

Cycloadditions that involve two unsymmetric reactants can lead to regioisomers. The regioselectivity of these adducts can be predicted with a high degree of success through the use of frontier molecular orbital theory.22 25 The ortho product (this nomenclature follows the analogy of disubstituted aromatic systems) is usually the preferred isomer from 1-substituted dienes, whereas 2-substituted dienes provide the para isomer as the major adduct. However, when a Lewis acid is used as a catalyst in the reaction, the ratio of these isomers can alter dramatically and, occasionally, can be reversed.22... 

The presence of a fluorine or a chlorine atom on the aromatic ring clearly leads to two different behaviors, giving two different products—aniline-1- or anilinium ion with formation of HX or X. Apparently, two different reaction coordinates are involved. In disubstituted aromatic compounds, depending on the nature of the substitutents, these two processes are competitive. 

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