Substitution by Carbon

The Suzuki reaction permits the palladium (Pd)-catalyzed substitution of a halogen (I Br Cl) attached to an alkyl, alkenyl, or aryl group by a second alkyl, alkenyl, or aryl group, originally attached to boron and with retention of stereochemistry (see Miyaura et al, 1979). 

Processes similar to the Suzuki coupling reaction have been observed with alkynes. Thus, the Stephens-Castro reaction between unsaturated iodides (aryl, vinyl) and copper(l) acetylides in pyridine solvent results in the formation of new 

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For a review of substitution by carbon groups on a nitrogen hctcrocyclc. sec Vorbruggcn Maas Heterocvcles 1988, 27. 2659-2776. For a related review, see Comins O Connor Adv. Heterocycl. Chem. 1988, 44. 199-267. 

E. Substitution by Carbon In these reactions a new carbon-carbon bond is formed, and they may be given the collective title coupling reactions. In each case an alkyl or aryl radical is generated and then combines with another radical (a termination process) or attacks an aromatic ring or olefin to give the coupling product.276... 

A DFT study of the geometrical, electronic, and energetic parameters of fluoro derivatives of diphenylborates 9 and 10 and isoelectronic structures where the central atom has been substituted by carbon and nitrogen has also been carried out <2005TA755>. The relative energy of the homochiral versus heterochiral complex has been linearly correlated with the central atom and fluorine substitution on the different positions of the aromatic ring. 

Yli-Kauhaluoma JT, Janda KD. Catalytic antibodies the rerouting of chemical reactions. Towards electrophiUc aromatic substitution by carbon dioxide. Ann. N.Y. Acad. Sci. 1996 799 26-31. Baldwin JE. Approach vector analysis A stereochemical approach to reactivity. J. Chem. Soc., Chem. Commun. 1976 (18) 738-741. 

Besides protons a series of heteroligands in the a-position of phosphonium ylides can also be substituted, giving rise to the formation of new alkylidenephosphoranes. Halogen atoms have been substituted by carbon groups (with lithium organyls or acyl chlorides) or another halogen. Reaction of a-lithiated ylides (see equation 35) or ylide anions with electrophiles may be considered as substitution of an alkali metal substituent at the ylide carbon atom. 

Moreover, the composite reference ETA index, denoted as tir, is calculated as the composite ETA index from a molecular graph where all heteroatoms are substituted by carbon atoms and all the multiple bonds by single bonds. Then, the functionality index Tip is defined as the difference between the composite reference ETA index and the composite ETA index ... 

Substitution by carbon and sulfur electrophiles at the 2-position may be achieved by activation of oxazole with a 2-trimethylsUyl group. For example, 4-methyl-2-trimethylsilyloxazole (49) reacts with aldehydes to give silyl ethers, it reacts with acyl chlorides to give acyl derivatives, and it reacts with phenylsulfenyl chlorides to give a mixtm-e of 2-phenylthio and 2,5-di(phenylthio)oxazole <87JOC34l3>. Reactions with two a-chiral aldehydes, (R)-2,3-0-isopropylideneglyceraldehyde and... 

In addition to the very important palladium-catalysed reactions, boronic acids undergo a number of useful reactions that do not require transition-metal catalysis, particularly those involving electrophilic ipso-substitutions by carbon electrophiles. The Petasis reaction involves ip,y(9-replacement of boron under Mannich-like conditions and is successful with electron-rich heterocyclic boronic acids. A variety of quinolines and isoquinolines, activated by ethyl pyrocarbonate, have been used as the Mannich reagent . A Petasis reaction on indole 3-boronic acids under standard conditions was an efficient route to very high de a-indolylglycines. " ... 

The alkoxy group has been substituted by hydroxy, alkylsulfanyl, amino or hydrazino groups233 234 and can also be substituted by carbon nucleophiles.240... 

Four reviews on allylic substitution reactions have been published. The first deals with the enantioselective allylic substitutions by carbon nucleophiles, in the presence of both palladium and non-palladium catalysts. The second reviews stere- 0 oselective allylic substitution reactions forming asymmetric C-C, C-N, and C-O bonds. The third review covers new developments in metal-catalysed asymmetric 0 allylic substitution reactions with heteroatom-centred nucleophiles. Several applications of this new methodology are included. Finally, the catalytic 5 2 and 5 2 reactions of allylic alcohols, most of which occur with a very high ee, have been reviewed. ... 

DMTSF reacts with flavan-3-ol-based benzyl sulfides with activation of the C4-S bond towards substitution by carbon nucleophiles, allowing the formation of the interfiavanyl bond in procyanidins (eq 14). ... 

When the polymer was heated in the solid state or in solution aromatization occurred, accompanied by elimination of two ROH molecules for each phenylene group formed. For practical reasons, aromatization was performed preferentially on PCHD substituted by carbonate moieties (R = CH3-OCO-) (17), which on thermal decomposition gave methanol and carbon dioxide (Scheme 6.7) [33]. 

A bitter taste appears to be a common feature of a base. It is a fact that many medicinal substances are nitrogen bases, substances that organic chemists call amines. Such substances are considered derivatives of ammonia, in which one or more hydrogen atoms have been substituted by carbon-containing groups. Here, for example, are the structures of some amines ... 

Leucine is known to be a precursor of neoaspergillic acid and pulcherriminic acid, and MacDonald s results would seem to rule out a role of the N-hydroxyamino acids as intermediates in the biosynthesis of these hydroxamates, although direct experiments using the hydroxylamino acids as substrates would be desirable. In the aspergillic acid family, it thus appears that the amino acid nitrogen undergoes substitution by carbon prior to its oxidation (oxygenation ). 

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