Alkyl derivatives ring systems

CpMoX and Derivatives. [CPM0X4] (X = Cl, Br) are best synthesized by oxidation of [CpMoMe(CO)3] with PCI5 or PBrs. The tetrachloride may also be prepared on treatment of [CpMoO(Cl)2] with HCl. These Mo compounds may be reduced to lower valent species. Thus, treatment of [CpMoCLt] with zinc affords the insoluble molybdenum(III) compound [(CpMoCh) ]. Enhanced solubility is obtained through the use of alkylated cyclopentadienyl ring systems. The Mo complexes are best prepared by one of two methods ... 

Thiophene [110-02-1] and a number of its derivatives are significant in fine chemical industries as intermediates to many products for pharmaceutical, agrochemical, dyestuffs, and electronic appHcations. This article concentrates on the industrial, commercial, and economic aspects of the production and apphcations of thiophene and thiophene derivatives and details the main synthetic schemes to the parent ring system and simple alkyl and aryl derivatives. Functionalization of the ring and the synthesis of some functional derivatives that result, not from the parent ring system, but by direct ring cyclization reactions are also considered. Many good reviews on the chemistry of thiophene and thiophene derivatives are available (1 7). 

By reaction of thiosemicarbazide or its 4-alkyl derivatives with nitrous acid Freund and co-workers in 1896 prepared compounds which were formulated as amino or alkylamino derivatives of the ring system 1,2,3,4-thiatriazole (1). Oliveri-Mandala, however, argued that these compounds are actually thioazides (2), and this view seems to have been generally accepted (e.g. in Beilstein s Handbuch) until... 

The initial series of major tranquilizers consists of alkylated derivatives of 4-aryl-4-hydroxypiperidines. Construction of this ring system is accomplished by a set of rather unusual reactions. Condensation of methylstyrenes with formaldehyde and ammonium chloride afford the corresponding hexahydro-1,3-oxazines (119). Heating these oxazines in the presence of acid leads to rearrangement with loss of water to the tetrahydropyridines. Scheme 1 shows a possible reaction pathway for these transformations. Addition of hydrogen bromide affords the expected 4-bromo compound (121). This last is easily displaced by water to lead to the desired alcohol (122) The side chain (123) is obtained by Friedel-Crafts acylation of p-fluorobenzene with 4-chloro-butyryl chloride. Alkylation of the appropriate arylpiperidinol with 123 affords the desired butyrophenone derivative. Thus,... 

Scheme 10.17 illustrates allylation by reaction of radical intermediates with allyl stannanes. The first entry uses a carbohydrate-derived xanthate as the radical source. The addition in this case is highly stereoselective because the shape of the bicyclic ring system provides a steric bias. In Entry 2, a primary phenylthiocar-bonate ester is used as the radical source. In Entry 3, the allyl group is introduced at a rather congested carbon. The reaction is completely stereoselective, presumably because of steric features of the tricyclic system. In Entry 4, a primary selenide serves as the radical source. Entry 5 involves a tandem alkylation-allylation with triethylboron generating the ethyl radical that initiates the reaction. This reaction was done in the presence of a Lewis acid, but lanthanide salts also give good results. 

A wide range of derivatives of the bicylic ring systems RCN5S3 (108, R=alkyl, aryl, CF3, NR 2, Cl) have been prepared and structurally characterized.265 Two synthetic routes are available (a) reaction of. SVV -dichlorodithiatriazines with (Me3SiN)2S (Equation 4) and (b) reactions of trisilylated benzamidines with (NSC1)3. 

So far, only the ring system of ervitsine has been synthesized. Exploiting the regiospecific alkylation of a 2-cyano-3-piperideine derivative 279, Husson et al. (196) obtained 280, whose stereochemistry was determined by X-ray analysis (Scheme 5). 

The utilization of the Robinson annellation method for the synthesis of cory-nanthe-type alkaloids has been thoroughly investigated by Kametani and coworkers (149-152). The tetracyclic ring system was efficiently formed via the Michael addition of dimethyl 3-methoxyallylidenemalonate (247) to the enamine derived from 3,4-dihydro-1 -methyl-(3-carboline (150). Alkylation of 248, followed by hydrolysis and decarboxylation, resulted in a mixture of stereosiomeric enamides 250 and 251. Hydrogenation of 250 afforded two lactams in a ratio of 2 1 in favor of the pseudo stereoisomer 253 over the normal isomer 252. On the other hand, catalytic reduction of 251 gave 254 as the sole product in nearly quantitative yield. Deprotection of 254, followed by lithium aluminum hydride reduction, yielded ( )-corynantheidol (255) with alio relative configuration of stereo centers at C-3, C-15 and C-20. Similar transformations of 252 and 253 lead to ( )-dihydrocorynantheol and ( )-hirsutinol (238), respectively, from which the latter is identical with ( )-3-epidihydrocorynantheol (149-151.). 

Alkylation of the pyridine-like nitrogen in 1 with the Meerwein s salt allowed the preparation of a derivative 2 of this ring system suitable for the evaluation of intercalating properties (Scheme 1) <2000BML1767, 1996BML2831>. 

The azide derivatives 269 of urocanic acid undergo thermolysis to give 270 in moderate yields, presumably via cyclization of the isocyanate and migration of the alkyl group R (Equation 53) <2002TL5879>. When R is larger than ethyl, a different ring system is formed instead. 

The reaction of the 3-(bromomethyl)pyrazole 276 with various alkyl derivatives of tosylmethyl isocyanide (TosMIC) 277 affords the products 278 (Equation 56) and requires phase-transfer conditions for success <2005JOC4879>. This reaction was also used for the synthesis of ring system 68, but in lower yield (25%). 

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