C-heteroatom

Electron donation from pyrrole-like nitrogen, or to a lesser extent from analogous sulft or oxygen atoms, helps electrophilic attack at azole carbon atoms, but as the number c heteroatoms in the ring increases, the tendency toward electrophilic attack at both C an N decreases rapidly. 

Cobalt-catalyzed C—C and C-heteroatom bond formation in transformations of heterocycles 97SL876. 

Benzylic, allylic and propargylic positions enhance the cathodic cleavage rate of C— heteroatom bonds as, for example, in the reduction of benzylic and allylic halides or alcohols56. Similar activated sulphones, due to their acidity, are in a class apart. Figure 8 shows the similitude between the cathodic behaviour of an allylic sulphone and its isomer, i.e., the corresponding vinylic sulphone when the electrolyses are run in an aprotic solvent. However, in the presence of an excess of proton donor, discrepancies appear. 

Examples of "very tnixed"-metal cluster-assisted C-heteroatom bond formation are still rare, with both literature extant examples involving coupling of bridging phosphido ligand with a C-ligand. Phosphido, hydrido, and alky tie were assembled stereospecilically to afford PPh2(( /.v-CR=CHR) (Fig. 29),-" while an unusual... 

Hydrogenation of substrates having a polar multiple C-heteroatom bond such as ketones or aldehydes has attracted significant attention because the alcohols obtained by this hydrogenation are important building blocks. Usually ruthenium, rhodium, and iridium catalysts are used in these reactions [32-36]. Nowadays, it is expected that an iron catalyst is becoming an alternative material to these precious-metal catalysts. 

Transition metal-catalyzed carbenoid transfer reactions, such as alkene cyclopro-panation, C-H insertion, X-H insertion (X = heteroatom), ylide formation, and cycloaddition, are powerful methods for the construction of C-C and C-heteroatom bonds [1-6]. In contrast to a free carbene, metallocarbene-mediated reactions often proceed stereo- and regioselectively under mild conditions with tolerance to a wide range of functionalities. The reactivity and selectivity of metallocarbenes can be... 

Me3SiCl reacts with phosphinomethanides I (R=Me) with at least one hydrogen as carbanion substituent (X = Y=H X=H, Y=SiMe3, PMej) via Si-C bond formation to give heteroelement substituted phosphinomethanides [4]. With fully C-heteroatom-substituted I, the reaction depends on the nature of X and Y, as shown by Eqs. (l)-(3) ... 

The Zr atom of the C—Zr bond has been replaced with H, D, and several non-metallic heteroatoms, such as Cl, Br, I, and O. Although some reactions of RZrCp2Cl, where R is an alkyl or alkenyl group, with S02 and NO [95,96] are known, very little is known beyond them about the formation of C—S, C—N, C—P, and other C—heteroatom bonds containing Group 15 and 16 atoms. 

Cathodic substitution stands for C,C bond or C, heteroatom bond formation with cathodically generated anions. The question of regioselectivity is encountered in the reaction of such anions with allyl halides (path a) or in the reaction of allyl anions generated in an ECE process from allyl halides (path b). Cathodic reductive silylation of an allyl halide proceeds regioselectively at the less substituted position (Fig. 15) [91]. From the reduction potentials of the halides it is proposed that the reaction follows path b. 

Knoelker H-J (2005) Occurrence, Biological Activity, and Convergent OrganometaUic Synthesis of Carbazole Alkaloids. 244 115-148 Kolodziejski W (2005) Solid-State NMR Studies of Bone. 246 235-270 Koser GF (2003) C-Heteroatom-Bond Forming Reactions. 224 137-172 Koser GF (2003) Heteroatom-Heteroatom-Bond Forming Reactions. 224 173-183... 

Appendix for polycyclic ring systems with C-heteroatom bonds... 

Alkyl, vinyl and aryl radicals can give homolytic substitution at a heteroatom either inter- or intramolecularly thus forming C-heteroatom bonds. 

We can insert the heteroatom into the rest of the carbon skeleton, or attempt to join two units, one of which contains the heteroatom, by means of C-C and C-heteroatom linkages. To make the new bonds, two reaction types are most frequently encountered. Heteroatom-C bond formation is achieved using the heteroatom as a nucleophile to attack an electrophile such as a carbonyl group (see Section 7.7.1). Aldol-type reactions may be exploited for C-C bond formation (see Section 10.3), employing enamines and enols/enolate anions (see Section 10.5). 

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