Arene substitution

A different reaction takes place when electrophiles react with arenes Substitution is observed instead of addition If we represent an arene by the general formula ArH where Ar stands for an aryl group the electrophihc portion of the reagent replaces one of the hydrogens on the ring... 

Yilmaz and Deligoz [47,48] prepared a calix[6]arene substituted with six aminoglyoxime groups (2), and two Wc-dioxime compounds of calix[4]arene (3,4), and they examined their chelating ability with Co, Cu, and NF. ... 

The other general method for the formation of arenes substituted by groups containing As or Sb bonded directly to an aromatic carbon atom is based on the use of arsenite and stibonite ions (HAsOf- and HSbC>3 ) or compounds which form similar or related ions in alkaline aqueous systems (AsC15, SbCl5 Scheme 10-91). 

Due to the inherent unsymmetric arene substitution pattern the benzannulation reaction creates a plane of chirality in the resulting tricarbonyl chromium complex, and - under achiral conditions - produces a racemic mixture of arene Cr(CO)3 complexes. Since the resolution of planar chiral arene chromium complexes can be rather tedious, diastereoselective benzannulation approaches towards optically pure planar chiral products appear highly attractive. This strategy requires the incorporation of chiral information into the starting materials which may be based on one of three options a stereogenic element can be introduced in the alkyne side chain, in the carbene carbon side chain or - most general and most attractive - in the heteroatom carbene side chain (Scheme 20). 

The well-defined copper complexes 94 and 95 (Fig. 2.16) have been used as catalysts for the intermolecular hydroamination of electron-deficient alkenes [Michael acceptors, X=CN, C(=0)Me, C(=0)(0Me)] and vinyl arenes substituted... 

Surprisingly, the organometallic catalyst shows good stability under the reaction conditions (CFjCOOH/CH Cl ). In the absence of 107 (Fig. 2.18), Pd(OAc)j under the same conditions catalyses the same reaction with reduced activity (ca. 50% conversion in 24 h) and different chemoselectivity. Arenes, substituted by electron-withdrawing snbstitnents react slower. Both internal and terminal alkynes undergo the reaction, however, the former require more forcing conditions [90],... 

A. Marra, M.-C. Schermann, A. Dondoni, A. Casnati, P. Minari, and R. Ungaro, Sugar calixarenes Preparation of calix[4]arenes substituted at the lower and upper rims with O-glycosyl groups, Angew. Chem. Int. Ed., 33 (1994) 2479-2481. 

Veiy recently it was disclosed, that the water-soluble dinuclear complex obtained in the reaction of [ RhCl(COD) 2] and 11-mercaptoundecanoic acid catalyzed the aqueous/organic biphasic hydroformylation of styrene and various arene-substituted styrenes with good activity and useful selectivity to the branched aldehydes (Scheme 4.6) [82], Below pH 4 the acid form of the complex [ Rh(p-S(CH2)ioC02H)(COD) 2] precipitated virtually quantitatively but could be redissolved in water on addition of base. Importantly, higher olefins could also be hydroformylated by this catalyst (for 1-octene TOP = 17.5 h at 55 °C, 35 bar syngas, n/i = 1.0). 

Arene Substitution via Nucleophilic Addition to Electron Deficient Arenes... 

Arenes substituted with OCH, CH, F, and Cl are converted in satisfactory yield to 4,4 -substituted biphenyls in the same way. 

Dialkoxy Calix[4]arene Substituted Benzocrown-6 Extraction Percentages (% ) of Alkali Picrates from Water into Dichloromethane... 

The 1,2 and 3,4 regioselectivity of the ortho addition of an alkene to an arene substituted with a strong donor substituent is, according to Houk, dominated by interaction of the benzene S orbital with the alkene -tt HOMO, because the A -tt interaction would result in a 2,3 ortho adduct. For an arene substituted with a strong donor, the donor substituent, rather than the approaching alkene, will determine the symmetry of the orbitals [188],... 

A similar dimerization was recently observed for thiocalix[4]arenes substituted by four CMPO-residues. 

C. Paradisi, Arene Substitution via Nucleophilic Addition to Electron Deficient Arenesin Comprehensive Organic Synthesis (B. M. Trost, I. Fleming, Eds.), Vol. 4, 423, Pergamon Press, Oxford, 1991. 

Arene-substituted alkenes can undergo radical-cation [4+2] cycloadditions with 1,3-dienes when they are irradiated in the presence of an electron acceptor (Sch. 13) [49]. Good levels of regio and stereoselectivity... 

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