Electrophilic addition reactions synthesis

The synthesis of polyhalide salts, R4NX , used in electrophilic substitution reactions, are described in Chapter 2 and H-bonded complexed salts with the free acid, R4NHX2, which are used for example in acid-catalysed cleavage reactions and in electrophilic addition reactions with alkenes, are often produced in situ [33], although the fluorides are obtained by modification of method I.I.I.B. [19, 34], The in situ formation of such salts can inhibit normal nucleophilic reactions [35, 36]. Quaternary ammonium chlorometallates have been synthesized from quaternary ammonium chlorides and transition metal chlorides, such as IrClj and PtCl4, and are highly efficient catalysts for phase-transfer reactions and for metal complex promoted reactions [37]. 

IZV118) and the formation of (31) is analogous to the reaction (197)->(98) via a four-membered 1,2-oxathietane 2,2-dioxide intermediate. Subsequent products derived from (31) by electrophilic addition reactions at the alkenic double bond have been described in Section 4.33.3.2.2 and the synthesis of 4,5-dichloro-l,3,2-dioxathiolane 2,2-dioxide (154) by chlorination of ethylene sulfate (18) is discussed in Section 4.33.3.5. Cyclic sulfites, on the other hand, cannot be halogenated without ring opening (cfSection 4.33.3.2.4). 

Such structure reactions have existed in organic chemistry since long. Wilson gives an example of classification of electrophilic addition reactions of alkenes and alkynes. Patterns in organometalhc chemistry with applications in organic synthesis have been discussed by Schwartz and Labinger. 

Cumene is prepared on a large scale from benzene and propylene as an intermediate in the synthesis of acetone and phenol. This makes it an inexpensive and readily available starting material for the production of Galaxolide . Three further electrophilic addition reactions complete the synthesis. Firstly, isoamylene is added, to form pentamethylindane, to which propylene oxide is added. Finally, treatment with formaldehyde leads, via the hemiacetal, to the isochroman. 

Electrophilic addition reactions of alkenes lead to the synthesis of alkyl halides, vicinal dihalides, halohydrins, alcohols, ethers, and alkanes. 

Section 17.20 Synthesis of Carboxylic Acid Derivatives 711 A cyclic ether can also be prepared by an intramolecular electrophilic addition reaction. 

Electrophilic Addition Reactions. Further work by Johnson on the biomimetic polyene olefin cyclization reactions has shown that asymmetric induction by a chiral centre remote from the initiating cationic centre is possible. This was shown by the preparation of 11 a-methylprogesterone and a stereospecific total synthesis of racemic 11 a-hydroxyprogesterone via this route (Scheme 48). > ... 

The use in organic synthesis of Co2(CO)6 -complexed alkyne groups to stabilise an adjacent (propargylic) carbenium ion centre and thus facilitate stepwise electrophilic addition reactions has been reviewed . 

Garbers, C. F., and F. Scott Terpenoid synthesis. V. Electrophilic addition reactions in the synthesis of the ocimenones, the rose oxides, and a pheromone of Ips paraconfusus. Tetrahedron Lett. 1976, 1625—1628. 

The intramolecular Michael addition11 of a nucleophilic oxygen to an a,/ -unsaturated ester constitutes an attractive alternative strategy for the synthesis of the pyran nucleus, a strategy that could conceivably be applied to the brevetoxin problem (see Scheme 2). For example, treatment of hydroxy a,/ -unsaturated ester 9 with sodium hydride furnishes an alkoxide ion that induces ring formation by attacking the electrophilic //-carbon of the unsaturated ester moiety. This base-induced intramolecular Michael addition reaction is a reversible process, and it ultimately affords the thermodynamically most stable product 10 (92% yield). 

It will be recalled that one of the key operations in the synthesis of IJK ring system 86 is the intramolecular conjugate addition reaction (see 90—>89, Scheme 17b) to form ring J. In the context of compound 90, the electrophilic a,/ -unsaturated ester moiety and the potentially nucleophilic tertiary hydroxyl group reside in proximal regions of space, a circumstance that would seem to favor the desired cyclization evept (see Scheme 19). Indeed, exposure of a solution of 90 in THFto sodium hydride (1 equiv.) for one hour at 25 °C results in the formation of compound 89 in 92% yield. In... 

Many mechanistic results on this electrophilic addition are available but most of them deal with the first steps of the reaction in which the ionic intermediate is formed, rather than with the last steps in which the products are obtained by nucleophilic attack on this intermediate (ref. 2). The present paper reports results on the selectivity of olefin bromination, which have been obtained more or less systematically with a view to improving the existing rules which are too naive to be useful in synthesis (ref. 3). 

The synthesis of a-substituted phosphonates 89, via the electrophilic addition of phosphorylated C-radicals 88 (generated by reaction of BujSnH to the readily accessible a-phosphoryl sulfides (or selenides)) and electrophilic addition to electron rich alkenes, has been described [57] (Scheme 26). A large excess of alkene is necessary to minimize the competitive formation of the undesired compound 90 resulting from direct reduction of the initial radical 88. The ratio 89/90 has been measured for each example. The synthesis of the a-mono- or a,a-di-substituted (R or phosphonates 89 shows that the free radical approach... 

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