4- Aryl-3,5-dimethyl

Durch Abspaltung des Benzoyl-Resles aus 4-Aryl-5-benzoyl-l,2-dimethyl-4,5-dihydro-imid-azolen mit Kaliumhydroxid in Wasser/Methanol werden in Ausbeuten von 71-86% 4-Aryl-1,2-dimethyl-imidazole erhalten417 (der Mechanismus dieser Reaktion ist bislang nicht ge-klart). 

The concept of in situ liberation of carbon monoxide would be even more attractive if a metal-free material could serve as the carbon monoxide source. In the ideal carbonylation method, the organic solvent itself could be exploited for controlled generation of carbon monoxide. In 2002, Wan et al. addressed this issue and developed a microwave-promoted carbamoylation process based on the commonly used solvent dimethylformamide (DMF) as the carbon monoxide precursor75. Firstly, it was discovered that aryl dimethyl amides were accessible from the corresponding bromides in the presence of a nucleophilic catalyst, imidazole (Scheme 2.34). Secondly, tertiary benzamides other than dimethylamides were synthesised by addition of 3 equiv of an external amine (Scheme 2.34). 

The demethylation of the arylmethyl ethers A in Figure 2.2 is run in dimethyl formamide (DMF structural formula see Figure 2.17) the fourfold demethylation of the aryl tetramethyl ether B is performed in molten salt and the monodemethylation of the aryl dimethyl ethers C in DMF. The selectivity of the latter reaction deserves comment. Compound C and lithium... 

Excess methyl iodide refluxed with diaryl ditellurium derivatives produced aryl methyl tellurium diiodide and aryl dimethyl telluronium iodides. 

The following aryl methyl tellurium compounds were prepared from the aryl dimethyl telluronium iodides in refluxing pyridine. 

Lithium arenetellurolates and two or more moles of methyl iodide react to produce aryl dimethyl telluronium iodides3. 

The following aryl dimethyl telluronium iodides were similarly prepared ... 

When refluxed in excess methyl iodide, diaryl ditellurium compounds produced aryl dimethyl telluronium iodides as one of the products3,4 (Vol. IX, p. 1078). 

The MNK rearrangement proceeded smoothly to furnish S-aryl dimethyl-thiocarbamate. A temperature of 280 °C was necessary for clean conversion. Eventual hydrolysis with sodium hydroxide and acidification with dilute acid chloride promoted the cyclisation to thiocoumarin 83. 

A stepwise mechanism with a rate-limiting leaving group expulsion from the intermediate was proposed for the reactions of Z-aryl dimethyl- (43a), methylphenyl-(43b), and diphenyl-phosphinates (43c) with substituted anilines in DMSO at 333 K, based on the positive cross-interaction constants, The steric effects of the two ligands (R, R ) play a role in determining the reactivity of the phosphinates, but are relatively small compared to other phosphinate systems. A dominant frontside nucleophilic attack involving a hydrogen-bonded four-centre-type transition state (44) was proposed... 

The main limitations of the methodology are the low reactivity observed with ortho-substituted aryl(dimethyl)aluminium reagents and the competing methyl transfer-derived by-product which can be detected. Conversely, the addition of alkyl aluminium reagents to bulky substrates and non-aromatic enones proceeds with very high enantioselectivity, as exemplified in Fig. 6. 

In 2002, Alterman and coworkers exploited this concept and developed a micro-wave-promoted carbamoylation protocol using DM F as the in situ carbon monoxide liberator in septum-sealed reaction vials [40]. It was discovered that aryl dimethyl amides were accessible from the corresponding bromides in the presence of KOt-Bu and the nucleophilic catalyst, imidazole (Scheme 4.27). Moreover, tertiary benza-mides other than dimethylamides were prepared by adding 3 equiv. of an external primary or secondary amine. This in situ carbon monoxide generation methodology... 

Allenes also react with aryl and alkenyl halides, or triflates, and the 7r-allyl-palladium intermediates are trapped with carbon nucleophiles. The formation of 283 with malonate is an example[186]. The steroid skeleton 287 has been constructed by two-step reactions of allene with the enol trillate 284, followed by trapping with 2-methyl-l,3-cyclopentanedione (285) to give 286[187]. The inter- and intramolecular reactions of dimethyl 2,3-butenylmalonate (288) with iodobenzene afford the 3-cyclopentenedicarboxylate 289 as a main product) 188]. 

Goto et al. (386) have qualitatively studied the relationship between the structure and the ease of formation of some 2-aryl- and 2-heteroaryl-A-2-thiazolin-4-one derivatives. It is found that 2-pyridyI, 2-benzimidazoyl, and 2- 6 hydroxy-5 -methyl)-benzothiazolyl derivatives are too unstable to be isolated. 6 -Hydroxy-, 6 -methyl-, and unsubstituted 2-benzothiazoiyl derivatives, as well as naphtothiazolyl derivatives are unstable but isolable. On the other hand, 6 -methoxy-. 6 -acetoxy-. and 5, 7 -dimethyl-6 -hvdroxybenzothiazolyl derivatives as well as most of their 5-methyl substituted derivatives are stable and easily prepared. 

This method has been applied to the synthesis of 4-methyl (659), 4-aryl (416, 519, 659), 4,5-dimethyl (137, 220, 221), 4,5-dialkyl (229, 681), 4-methyl-5-O-acetoxyethyl) (229), 4-methyl-5-(j3-carbethoxyethyl) (229), 4-ary 1-5-bromo (579), and 2-chlorothiazoles from the corresponding a-thiocyanatoketones (Table 11-28). 

Other sulfur compounds such as thiourea, ammonium dithiocarbamate, or hydrogen sulfide also lead to 2-mercaptothiazoles. Thus thiourea has been used in the syntheses of 4,5-dimethyl (369) and 4-aryl-2-mercapto-thiazoles (Table 11-30) (519). The reactions were carried out by condensing the ia -thiocyanatoketones with thiourea in alcohol and water acidified with hydrochloric acid. By this procedure, 4-aryl-2-mercaptothiazoles were obtained in yields of 40 to 80% with bis-(4-aryl-2-thiazolyl) sulfides as by-products (519). These latter products (194) have also been observed as a result of the action of thiourea on 2-chloro-4-arylthiazole under the same experimental conditions. They can be separated from 2-mercaptothiazoles because of their different degrees of solubility in sodium hydroxide solution at 5%. In this medium bis-(4-phenyl-2-thiazolyl)sulfide is... 

The reaction is of the 8 2 type and works best with primary and secondary alkyl halides Elimination is the only reaction observed with tertiary alkyl halides Aryl and vinyl halides do not react Dimethyl sulfoxide is the preferred solvent for this reaction but alcohols and water-alcohol mixtures have also been used... 

I itro-DisplacementPolymerization. The facile nucleophilic displacement of a nitro group on a phthalimide by an oxyanion has been used to prepare polyetherimides by heating bisphenoxides with bisnitrophthalimides (91). For example with 4,4 -dinitro monomers, a polymer with the Ultem backbone is prepared as follows (92). Because of the high reactivity of the nitro phthalimides, the polymerkation can be carried out at temperatures below 75°C. Relative reactivities are nitro compounds over halogens, Ai-aryl imides over A/-alkyl imides, and 3-substituents over 4-substituents. Solvents are usually dipolar aprotic Hquids such as dimethyl sulfoxide, and sometimes an aromatic Hquid is used, in addition. 

Sulfoxides are compounds that contain a sulfinyl group covalendy bonded at the sulfur atom to two carbon atoms. They have the general formula RS(0)R, ArS(0)Ar, and ArS(0)R, where Ar and Ar = aryl. Sulfoxides represent an intermediate oxidation level between sulfides and sulfones. The naturally occurring sulfoxides often are accompanied by the corresponding sulfides or sulfones. The only commercially important sulfoxide is the simplest member, dimethyl sulfoxide [67-68-5] (DMSO) or sulfinylbismethane. 

Photolysis of Cp2TiAr2 in benzene solution yields titanocene and a variety of aryl products derived both intra- and intermolecularly (293—297). Dimethyl titan ocene photolyzed in hydrocarbons yields methane, but the hydrogen is derived from the other methyl group and from the cyclopentadienyl rings, as demonstrated by deuteration. Photolysis in the presence of diphenylacetylene yields the dimeric titanocycle (28) and a titanomethylation product [65090-11-1]. 

C H Sb, however, both possess trigonal-bipyramidal geometry. In addition to compounds of the type R Sb, mixed compounds of the type R R Sb or R3R 25b, where R and R may be alkyl, alkenyl, alkynyl, or aryl groups, are known. Thus triethyl dimethyl antimony [67576-92-5], CgH2 Sb, has been prepared (197) ... 

Many other organometaUic compounds also react with carbonyl groups. Lithium alkyls and aryls add to the ester carbonyl group to give either an alcohol or an olefin. Lithium dimethyl cuprate has been used to prepare ketones from esters (41). Tebbe s reagent, Cp2TiCH2AlCl(CH2)2, where Cp = clyclopentadienyl, and other metal carbene complexes can convert the C=0 of esters to C=CR2 (42,43). 

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