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A kinetic and product study of the dichloroacetic acid catalyzed chlorination of 1-methylpyrrole with 3- and 4-substituted N-chlorobenzamides was carried out. Protonated N-chlorobenzamides served as carriers of CI+. A Hammett correlation was obtained with ρ=−0.68 (r=0.98, n=8). General acid catalysis was observed with α=0.48 (r=0.99 and n=7). The yields of 2-chlorination (84±0.7%) and 3-chlorination (2.6±0.4%) were essentially constant (constant intramolecular selectivity) as the substituent on the N-chlorobenzamide was varied. Observation of constant intramolecular selectivity indicated that two intermediates were formed during the acid catalyzed chlorination of 1-methylpyrrole with N-chlorobenzamides. The carrier method is applicable to all types of aromatic systems and limited only by the availability of suitable carrier molecules. 相似文献
996.
Isabel M. Gomez-Monterrey Alessia Bertamino Maria V. Diurno Paolo Grieco 《Tetrahedron》2006,62(34):8083-8088
A novel synthetic route of diaza-bridged heterocycles based on natural 3,9-diazabicyclo[3.3.1]non-6-ene scaffold has been accomplished. The synthetic approach consists of a Pictet-Spengler condensation of the l-Dopa-OMe with an appropriate aldehyde, Fmoc-Aa-H, followed by intramolecular lactamization. This approach generated two configurationally distinct products (cis and trans-isomers), increasing the stereochemical diversity of these compounds. The synthesized compounds are potentially useful in the discovery of novel pharmacologically active compounds. 相似文献
997.
Prunet J 《Angewandte Chemie (International ed. in English)》2003,42(25):2826-2830
(E)-Alkene units are frequently found in macrocyclic natural products. Among the reactions that form the double bond during the cyclization, the classical Horner-Emmons coupling is still frequently used with success. During the last decade, ring-closing metathesis has emerged as a very powerful tool for the synthesis of large rings, but the E/Z selectivity, which is rarely predictable, depends on many factors which will be discussed in this review. The best solution might be a two-step procedure involving ring-closing alkyne metathesis (RCAM) followed by stereoselective reduction of the macrocyclic alkyne unit to the corresponding E double bond. 相似文献
998.
D. B. Nilov A. V. Kadushkin N. P. Solov'eva Yu. N. Sheinker V. G. Granik 《Chemistry of Heterocyclic Compounds》2004,40(1):106-113
In thionation of cyclic N-cyanoamidines, a four-step process occurs that leads to derivatives of novel heterocyclic systems: 7,8-polymethyleneimidazo[4,5-d]-1,3,2-diazaphosphorin-2-thiones. We have studied the chemical and spectral properties of the compounds obtained. 相似文献
999.
Wei-Jun Fu 《Journal of organometallic chemistry》2007,692(4):740-745
Manganese(III) acetate-mediated tandem radical cyclization reactions of methylenecyclopropanes with methyl substituted dicarbonyl compounds in acetic acid give dihydronaphthalene derivatives in moderate yields under mild conditions. 相似文献
1000.
Aihua Zhou 《Tetrahedron letters》2005,46(22):3801-3805
2-Ethylthiazolines react with 2-halobenzoyl chlorides to form N-(2-halobenzoyl)-cyclic ketene-N,S-acetals, which undergo stereo-controlled radical cyclizations to afford (R,S,S)-3-alkyl-10-methyl-2,3,10,10a-tetrahydrothiazolo[3,2-b]isoquinolin-5-one and (R,R,S)-3-alkyl-10-methyl-2,3,10,10a-tetrahydrothiazolo[3,2-b]isoquinolin-5-one. 相似文献