Nucleophilic Acylation Reactions

This section describes the nucleophilic reactions—acyl transfer reactions mostly—promoted by micelles and polysoaps. The nucleophiles are imidazoles, oxyanions and thiols, the same catalytic groups found ubiquitously in the enzyme active site. These nucleophiles are remarkably activated in the anionic form in the presence of cationic micelles and cationic polysoaps. These results are explained by the concept of the hydrophobic ion pair (Kunitake et al.,... 

When a Br nsted base functions catalytically by sharing an electron pair with a proton, it is acting as a general base catalyst, but when it shares the electron with an atom other than the proton it is (by definition) acting as a nucleophile. This other atom (electrophilic site) is usually carbon, but in organic chemistry it might also be, for example, phosphorus or silicon, whereas in inorganic chemistry it could be the central metal ion in a coordination complex. Here we consider nucleophilic reactions at unsaturated carbon, primarily at carbonyl carbon. Nucleophilic reactions of carboxylic acid derivatives have been well studied. These acyl transfer reactions can be represented by... 

The power ofbiocatalysts for the production of chiral compounds can be elevated to a second stage when proper use of the process leads to a larger number of different enantioenriched products from the same reaction. Some efforts have been made in this direction because the enzyme can be selective to either nucleophile or acyl donor. The elegancy of the reaction is increased when the process is carried out for the resolution of both. Scheme 7.20 depicts this possibility [38]. 

The reactions in this chapter are classified according to the attacking atom of the nucleophile in the order O, S, N, halogen, H, C. For a given nucleophile, reactions are classified by the substrate and leaving group, with alkyl substrates usually considered before acyl ones. Nucleophilic substitutions at a sulfur atom are treated at the end. 

No products arising from a nucleophilic reaction at C-2 were observed. The reaction with acetic acid also takes place regioselectively at C-3, but the initially formed anfz-3-acetoxy product undergoes an acyl migration to give the anti-3-hydroxy-2-acetamino product (see Scheme 21). 

A few further general examples of zinc catalytic activity or reactivity include the following. Other zinc-containing systems include a zinc phenoxide/nickel(0) catalytic system that can be used to carry out the chemo- and regioselective cyclotrimerization of monoynes.934 Zinc homoenolates have been used as novel nucleophiles in acylation and addition reactions and shown to have general utility.935,936 Iron/zinc species have been used in the oxidation of hydrocarbons, and the selectivity and conditions examined.362 There are implications for the mechanism of metal-catalyzed iodosylbenzene reactions with olefins from the observation that zinc triflate and a dizinc complex catalyze these reactions.937... 

The addition of protons is certainly the most common nucleophilic reaction of reduced hydrocarbon species due to the almost ubiquitous availability of proton donors, which may or not be wanted. However, under strictly aprotic conditions it is also possible to add other electrophilic reagents such as alkyl halides, acyl halides, CO2, and SO2. 

New chiral auxiliaries for nucleophilic reactions have been prepared from 5-hydroxy-l-tetralone <2001TA2605> and myrtenal <2001TA3095> and their use in diastereoselective reactions has been evaluated. It was found that both the tetralone- <2003EJ0337, 2003JOC6619> and the myrtenal- <2003TA3225, 2005TA1837> derived 2-acyl-l,3-oxathianes reacted diastereoselectively with nucleophiles (Equations 60 and 61). 

Assume initial nucleophilic reaction (alkylation or acylation) is slowest step... 

The apparent fickleness of the acyl-pyrroles and -indoles in their reaction with carbanions to form new C—C bonds arises from the contribution made by the zwitterionic structure, e.g. (410b), to the resonance hybrid and the choice of the reaction conditions is critical for a successful nucleophilic reaction. Thus, formyl-pyrroles and -indoles do not normally undergo the Cannizzaro reaction nor do they form stable cyanohydrins or undergo benzoin-type reactions. However, surprisingly, 2-formylpyrrole reacts with arylaldehydes in the presence of potassium cyanide to yield (428), which is easily oxidized to (429) (B-77MI30505). It is noteworthy that the presence of an ester substituent adjacent to the formyl group modifies the mesomeric interaction to such an extent to allow the formation of (430) in low yield, as a result of an initial benzoin-type self-condensation (Scheme 76) (68BSF637). 

H-1,2- Diazepines acylation, 7, 602 nucleophilic reactions, 7, 603 protonation, 7, 601 from pyrylium salts, 3, 660 4-subs tituted synthesis, 7, 604 synthesis, 7, 598, 599 thermal reactions, 7, 600... 

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