Nudeophilic substitution

It is interesting that the reaction of triphenylphosphine with a 1,2-allenyl ketone leads to the formation of a vinyl phosphonium salt 449, which upon protection of the carbonyl group would accept nucleophilic attack followed by elimination in the presence of Et3N to afford y-nudeophile substituted- ,/j-unsaturated enones 451 [197]. 

Zhang, X.-M. Yang, D.-L. Liu, Y.-C. Effects of electron acceptors and radical scavengers on nonchain radical nudeophilic substitution reactions. J. Org. Chem. 1993, 58, 224—227. 

The intramolecular nudeophilic substitution reaction - for example, the William-son-type reaction - represents one of the important methods for preparing oxetane ring structures, and have been widely applied to the synthesis of oxetanes (Scheme 7.1) [10]. Unfortunately, side reactions - which indude fragmentation from the intermediary alkoxide anion or elimination from the intermediary carboca-tion - often decrease the chemical yields of oxetane formation. 

Nudeophilic substitution chi 5 electrons Detennination of mechanism cli39... 

Table 5.9. Rate Constants for Nudeophilic Substitution in Primary Alkyl Substrates ... 

The photocyanation of pyrene in a microchaimel through an oil-water interface was investigated by Ueno et al. [13]. The microchips employed are made of polystyrene by embossing with a silicone template. The phase transfer reaction proceeds in four steps as depicted in Figure 16.2. In the first step, a photoinduced electron transfer in the oil phase (polycarbonate) occurs from the aromatic hydrocarbon pyrene (DH) to the electron acceptor 1,4-dicyanobenzene (A). The cationic DH " radical is subsequently the target of the nucleophilic attack of the cyanide anion at the oil-water interface. The cyanated product DCN is insoluble in water and goes back into the oil phase. Experiments without a cyanide source (NaCN) in the aqueous phase show no reaction. Hence it can be excluded that the nudeophilic-substituted cyanide originates from the electron acceptor 1,4-dicyanobenzene. 

Nudeophilic substitution A reaction in which one nucleophile is substituted for another. 

Another common reaction of alkenes uses diatomic halogens such as bromine (Br2) to form 1,2-dibromides (see Chapter 10, Section 10.4.1). In this reaction, the alkene reacts as a Lewis base with the bromine atom to form a bromonium ion. When 1,3-butadiene (3) reacts with bromine, both 1,2 and 1,4 addition products are formed, just as with the HBr reaction. The products are 3,4-dibromo-l-butene (32) and a mixture otE- and Z-l,4-dibromo-2-butene (33 and 34). Initial reaction with bromine gives bromonium ion 29 however, when this reacts with bromide ion, there are two sites for reaction. If bromide attacks the less stericaUy hindered carbon atom, the product is 32, but the bromine ion may also attack the C=C unit to give products 33 + 34. Nucleophilic attack of this type is called an Sj reaction (nudeophilic substitution at an allylic carbon with displacement of the leaving group). 

In this Chspter, we discuss the structure, nomenclature, physical properties, and chemical properties of ethers and compare their physical properties with those of isomeric alcohols. Then we study the preparation and chemical properties of a group of cyclic efhers called epoxides. As we shall see, fheir most important reactions involve nudeophilic substitution. This chapter continues the discussion of S l and Sj 2 reaction mechanisms begun in Chapter 9 and continued into Chapter 10. 

Digestion o proteins also begins with a nudeophilic substitution reaction... 

Adrenaline (or epinephrine), a hormone secreted by the adrenal gland, increases blood pressure and heart rate, and dilates lung passages. Individuals often speak of the "rush of adrenaline" when undertaking a particularly strenuous or challenging activity. Adrenaline is made in the body by a simple organic reaction called nudeophilic substitution. In Chapter 7 we learn about the mechanism of nucleophilic substitution and how adrenaline is synthesized in organisms. 

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