Anisole, metal complexes

Activation of aromatic compounds by transition-metal complexes was initially studied with Cr(CO)3 complexes. Nucleophilic addition of 2-lithio-l,3-dithianes to arene-chromium(O) complexes 185 followed usually by iodine-promoted decomplexation affords the corresponding 2-arylated 1,3-dithianes 186. The reaction of //-(toluene)- and (anisole)tricarbonylchromium (185) with compound 161 gave mixtures (52 46 and 10 90, respectively) of ortho and meta substituted derivatives (186) (Scheme 54)244. The meta directing effect was also observed (mainly better than 95%) with amino and fluoro substituted complexes245. 

Cobalt.—Aromatic hydrocarbon hydrogenations with a discrete metal complex have now been achieved for the first time. Thus hydrogenation of benzene to cyclohexane proceeds slowly at 25 °C and < 760 mmHg pressure in the presence of [Co( y -C3HB)- P(OMe)3)3]. Alkylbenzenes are converted into alkylcyclohexanes, anisole into methoxycyclohexane, and ethylbenzoate into ethyl cyclohexenylcarboxylate. The suggested mechanism of reaction is summarized in Scheme 14. ... 

Arene-metal complexes have again featured in approaches to spirocyclic ring systems. Thus, Semmelhack s group has extended their studies of chromium hexacarbonyl complexes of anisoles to effect new total syntheses of the spiro-sesquiterpenes, acorenone (169) and acorenone B (170) (Scheme 25), In... 

The synthetic results indicated that both metal complexes efficiently catalyzed ROP at 100 °C in an anisole solution, and 2 showed much better controlled characteristics of ROP than 1 (Scheme 49). 

In 2009, Peris et al. reported the henzylation of arenes using complex 35b as catalyst (0.1 or 1 molyo). " Different benzylating agents such as benzyl alcohols, benzyl ethers or styrene derivatives were used in combination with toluene, xylenes, phenol and anisole [eqn (8.16)]. Catalyst 35b displayed high activities, except for a few cases, but poor selectivities for the ortholpara isomers were observed (40 60 to 10 90). Although a mixture of orthol N-alkylated/para products was obtained when anilines were used as substrates, the results compared well with those previously reported which made use of Bronsted acids or metal complexes as catalysts. 

The reactivities of hydrido(phenoxo) complexes of trons-[MH(OPh)L2] (6 M = Ni 7 M = Pt) (L = phosphine) were examined (Eqs. 6.29, 6.30 Scheme 6-16), and a high nucleophiUdty for the metal-bound phenoxide was suggested [9, 10]. Reaction with methyl iodide produced anisole and trans-[MH(I)L2] for both Ni and Pt complexes. Phenyl isocyanate also provided the insertion products into the metal-phenoxo... 

The combination of ortho metallation and meta nucleophilic acylation was used to prepare a key intermediate in a synthesis of deoxyfrenolicin (42), as outlined in Scheme 11. The complex of anisole is orf/io-metallated with n-butyllithium and quenched with chlorotrimethylsilane the resulting [(o-(tri-methylsilyl)anisole)Cr(CO)3] (43) is then metallated again, converted to the arylcuprate, and coupled with ( )-2-hexenyl bromide to give the complex of l-trimethylsilyl-2-methoxy-3-(2-hexenyl)benzene (44). Addition of the carbanion from the cyanohydrin acetal of 4-pentenal, followed by the standard iodine oxidation and subsequent hydrolysis of the cyanohydrin acetal to regenerate the carbonyl group... 

Transition-metal-catalyzed hydroboration, a reduction using B H bonds, of styrene derivatives has been demonstrated to occur in supercritical carbon dioxide using tunable Rh(I) complexes as catalysts. In the case of vinyl anisole (eq. 2.5), significantly higher regioselectivities were reported for the reaction in this medium than in THF or perfluoro(methylcyclohexane) (Carter et ah, 2000). 

A peculiar complex is formed by if coordination of Os(II) ammine complex to one of the double bonds of benzene rings, rather than rf coordination, and the coordinated benzene rings show interesting reactivity [82]. For example, Os(II) coordinates regioselectively to the 2,3-double bond of anisole to form the complex 333, and hence localization of the remaining 7r-electrons occurs. As a result, at 20 °C an electrophile attacks easily at C(4) due to electron-donation of the methoxy group. The 4H-cationic intermediate 334 is stabilized by backdonation from the metal, and the monosubstitution product 334 is formed without deprotonation. The / ara-substituted anisole 335 is... 

The pentaammineosmium(II) metal center also binds in a dihapto fashion to several other classes of aromatic molecules, including benzenes, naphthalenes, phenols, anisoles, anilines, furans, and thiophenes, activating them toward further functionalization. The reactivity and synthetic utility of these complexes are the subject of a recent review Harman, W. D. Chem. Rev. 1997, 97,1953. 

Almost all rj2-arene complexes of [Os] are amenable to both intrafacial (i.e., ring-walk) and interfacial (i.e., face-flip) isomerization mechanisms, which allow the metal to coordinate to the most thermodynamically favorable position (Figure 2). Aromatic molecules bearing a redonor group (e.g., anisole, aniline, phenol) tend to place the metal across C5-C6 in order to... 

Steric arguments suggest that the addition of dihydrogen to [Os]-arenes should occur on the arene face opposite that of metal coordination. This theory is supported by the generation of l-d4 upon the partial deuteration of 1. Furthermore, the hydrogenation of complexed anisole (5) under anhydrous conditions yields complexed 3-methoxycyclohexene (6), in which the methoxy group is syn to the metal. It was found, however, a trace of water in the reaction mixture results in the formation of complexed cydohexenone (7), presumably from the attack of water on the dihydroanisole intermediate [13]. 

In the presence of Lewis acids, N-substituted aniline complexes of [Os] also add electrophiles at C4, again at the arene face opposite to that involved in metal coordination. This reaction has been shown to be general for a broader range of Michael acceptors than may be utilized with anisole complexes of [Os]. The N-ethyl aniline complex, for example, adds Michael acceptors and acetals in yields ranging from 53-95 % (Table 13, entries 1-6) [27]. The N,N-dimethyl aniline complex (entries 7-9) also adds Michael acceptors to C4 in moderate to high yields (Table 13) and adds to the <5-carbon of an a,/ ,y,<5-un saturated ester (entry 3). 

Metal fragments of the form (TpRe(CO)(L), in which L = Melm or NH3, have the ability to bind substituted benzenes in an 2-fashion. The fragment having L = Melm has seen more application because of difficulties associated with the synthesis and isolation of aromatic complexes having L = NH3. Anisoles, phenols, and naphthalenes all form thermally stable -complexes when stirred in excess (10-25 equiv.) with TpRe(CO)(MeIm)( /2-benzene) in THF. The complexes are typically isolated by precipitation from hexanes. The benzene complex can be prepared by direct reduction of the Re(III) precursor, TpRe(MeIm)(Br)2, with Na° in benzene under one atmosphere of CO [35]. 

Some antioxidants possess antimicrobial properties, such as propyl gallate and butylated hydroxy anisole, which are somewhat effective against bacteria. Butylated hydroxy toluene has demonstrated some antiviral activity. Compatibility of antioxidants with the drug, packaging system and the body should be studied carefully. For example, tocopherols may be absorbed onto plastics ascorbic acid is incompatible with alkalis, heavy metals, and oxidizing materials such as phenylephrine, and sodium nitrite and propyl gallate forms complexes with metal ions such as sodium, potassium and iron. 

Similar ortfo-metallation products have been obtained from reactions of (775 7]1-CsMe4SiMe2NBut) Y(CH2SiMe3)(THF) with anisole and 3- and 4-methylanisole.290 Both the lutetium and ytterbium alkyl complexes were subjected to hydrogenolysis with dihydrogen or with phenylsilane in pentane at room temperature to give the... 

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