Reaction termination reagent effect

The observed rate law is then three-halves order in the reagent A2. In most real systems, the situation is complicated because more than one termination reaction makes a contribution to the total termination rate. A more complete discussion of the effect of termination steps on the form of the rate law has been given by Huyser. ... 

Terminal alkynes can be converted readily into alkynylsilanes by reaction of the corresponding alkyne anion or its metalloid equivalent with a suitable chlorosilane (/). The reverse reaction, that of liberation of the alkyne, is quite facile, being effected by several reagent combinations, including hydroxide ion, methanolysis, fluoride anion, silver(i) followed by cyanide anion, and methyl lithium-lithium bromide (2). 

Trialkylsilyl groups have a modest stabilizing effect on adjacent carbanions (see Part A, Section 3.4.2). Reaction of the carbanions with carbonyl compounds gives (3-hydroxyalkylsilanes. (3-Hydroxyalkylsilanes are converted to alkenes by either acid or base.270 These eliminations provide the basis for a synthesis of alkenes. The reaction is sometimes called the Peterson reaction.211 For example, the Grignard reagent derived from chloromethyltrimethylsilane adds to an aldehyde or ketone and the intermediate can be converted to a terminal alkene by acid or base.272... 

The reactivity order of alkenes is that expected for attack by an electrophilic reagent. Reactivity increases with the number of alkyl substituents.163 Terminal alkenes are relatively inert. The reaction has a low AHl and relative reactivity is dominated by entropic factors.164 Steric effects govern the direction of approach of the oxygen, so the hydroperoxy group is usually introduced on the less hindered face of the double bond. A key mechanistic issue in singlet oxygen oxidations is whether it is a concerted process or involves an intermediate formulated as a pcrcpoxide. Most of the available evidence points to the perepoxide mechanism.165... 

Figure 1.61 Traut s reagent can undergo side reactions after the modification of an amine-containing molecule. The terminal thiol group can recyclize to create another iminothiolane derivative that effectively ties up the thiol.

This reaction mechanism has already been reported.23,24 The mechanism is actually quite significant for the economics and efficiency of the preparative chemistry. The fact that an S 2 mechanism is not in effect here means that only a slight stoichiometric excess of the fluorocarbon reagent is required for good yields of the intermediate products. Also, the action of an S 2 mechanism would make the desired product itself susceptible to a second nucleophilic attack on the terminal -CF2Br, resulting primarily in the production of polymer from this reaction instead of the observed product. 

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