Carbon nucleophilic attack

No reaction of soft carbon nucleophiles takes place with propargylic acet-ates[37], but soft carbon nucleophiles, such as / -keto esters and malonates, react with propargylic carbonates under neutral conditions using dppe as a ligand. The carbon nucleophile attacks the central carbon of the cr-allenylpal-ladium complex 81 to form the rr-allylpalladium complex 82, which reacts further with the carbon nucleophile to give the alkene 83. Thus two molecules of the a-monosubstituted /3-keto ester 84, which has one active proton, are... 

Ring-atomic centers can undergo attack by electrophiles, easily at the ring nitrogen and less easily at ring carbons. Nucleophilic attack is also possible at ring carbons or hydrogens. 

In contrast, soft carbon nucleophiles attack at C5. The reaction of 23 with diethylaminopropyne yields alkenyl(amino)pentatetraenylidene complexes (34) by insertion of the C = C bond of the alkyne into the C4=C5 bond of the pentatetrae-nylidene ligand [9]. The reaction is initiated by a nucleophilic attack of the ynamine at C5 followed by ring closure and electrocyclic ring opening (Scheme 3.34). Complexes 34 are obtained as mixtures of s-cis/s-trans isomers. 

Thermal and Photochemical Reactions Electrophilic Attack at Nitrogen Electrophilic Attack at Carbon Nucleophilic Attack at Carbon Nucleophilic Attack at Hydrogen Reduction Oxidation... 

The oxazole ring possesses less aromatic stabilization than a thiazole ring and is readily opened in many of its fused derivatives, especially in oxazolium salts. In the pyridazinium derivative (191) the oxazole ring is opened by oxygen, sulfur or carbon nucleophilic attack at the C-8a ring junction (77YZ422). In the mesoionic pyridine (192) an amine attacks at C-2, which is a pseudocarbonyl carbon atom (70JCS(C)1485). 

Since the soft carbon nucleophiles attack the Ti-allyl group from the side opposite to palladium, the asymmetric induction at the carbon nucleophiles is difficult with... 

In the first step of acetal (or ketal) formation, the acid protonates the carbonyl oxygen, making the carbonyl carbon more susceptible to nucleophilic attack (Figure 18.3). Loss of a proton from the protonated tetrahedral intermediate gives the hemiacetal (or hemiketal). Because the reaction is carried out in an acidic solution, the hemiacetal (or hemiketal) is in equilibrium with its protonated form. The two oxygen atoms of the hemiacetal (or hemiketal) are equally basic, so either one can be protonated. Loss of water from the tetrahedral intermediate with a protonated OH group forms a compound that is very reactive because of its electron-deficient carbon. Nucleophilic attack on this compound by a second molecule of alcohol, followed by loss of a proton, forms the acetal (or ketal). 

Nucleophiles that are also strong bases react with the electrophilic hydrogen of an alcohol rather than the electrophilic carbon. Nucleophilic attack at carbon would need the loss of a hydroxide ion in a nucleophilic substitution reaction. However, this is not favoured as the hydroxide ion is a strong base and a poor leaving group (Fig. A). However, reactions which involve the cleavage of an alcohol s C-O bond are... 

The [i-aUyl complexes can react with several types of nucleophiles, giving rise to the corresponding substitution products. O- and N-nucleophiles as well as soft carbon nucleophiles attack the t-allyl complex directly at the aUylic position, while hard C-nucleophiles react via transmetaUations [2c, 3]. If the nucleophihc attack occurs under an atmosphere of CO, insertion of CO can occur, yielding carbonyl compounds [4]. Alkenes and aUcynes can also insert into allyhnetal bonds, a protocol that is used preferentially for cycUzations [5]. Cyclizations can also occur, if the 7t-allylmetal complex contains an internal nucleophilic center. If the metalallyl complex acts as a nucleophile, direct coupling with aryl halides [6] or additions to electrophiles such as aldehydes, ketones, or imines are possible [7]. This review focuses on C-C coupling reactions via these tt-allyhnetal (or in some cases, a-allyhnetal) intermediates. 

Predominant formation of the C-benzylated product can be understood by considering the soft carbon nucleophile attacking the benzyl carbon of the oxosulfonium trilluoromethane sulfonate, with diphenyl sulfoxide acting as a soft leaving group. The reaction also proceeds smoothly with various other substituted benzyl alcohols with moderate to good yields. Sodium enolates derived from esters, a-cyano esters, a-aromatic and aliphatic ketones can also be benzylated with consistent high yields. 

A soft carbon nucleophile attacks the sp carbon of the allenylpalladium complex A to give a TT-aUylpalladium complex. Another soft carbon nucleophile attacks the Tr-aUylpal-ladium complex thus formed to afford an alkene, into which the same nucleophiles are doubly introduced (Schemes 7 and The reaction with /S-keto esters provides... 

---