Redistribution allyls

Reactions of tetraallylstannanes with aldehydes catalyzed by SnCl4 also appear to involve a halostannane intermediate. It can be demonstrated by NMR that there is a rapid redistribution of the allyl group.174 Reactions with these halostannanes are believed to proceed through a cyclic TS. 

Here the CH2 is presumed to insert into the methyl CH bond. If the reaction occurred through a radical intermediate, a symmetrical allyl radical would have been obtained which on recombination would have had the C -activity redistributed equally between terminal olefin and the 3-position ... 

Until relatively recently, less attention has been given to catalysis of redistribution reactions by transition metal complexes. Redistributions have been observed during the course of platinum-catalyzed hydrosila-tion hence, the scrambling reaction can be a nuisance by decreasing the yield of desired hydrosilation products. A noteworthy example is the H/Cl exchange that occurs during the hydrosilation of allyl chloride [Eq. (10)]. 

In the presence of a catalytic amount of aluminum chloride, hydrogen chloride, or trimethylchlorosilane also undergoes cleavage of the Si bond. The latter is an example of a redistribution reaction (equation 40). Facile cleavage of the allyl-silicon bond has been utilized for the preparation of iodotrimethylsilane (equation 41). ... 

Write the mechanism for the redistribution of the electrons within the n bond and pz orbital system so as to give the other canonical structure of this allylic cation. 

If redistribution proceeds through the formation of three-center, two-electron bonds (Scheme 1), alkenyl, aryl, alkynyl, allyl, benzyl and propargyl groups should participate more readily than the alkyl group, but this point is not established. Catalysis by boron hydrides is not applicable where alkenyl or alkynyl groups are present, because the boron hydrides are consumed through hydroboration. 

The allyl radical can be represented as a hybrid of two contributing structures. Here, fishhook arrows show the redistribution of single electrons between contributing structures. Note that three v electrons take part in this resonance. 

One example of the Claisen rearrangement transforms allyl phenol ethers to o-allylphenols through the redistribution of she electrons in a cyclic transition state. 

The Ciaisen Rearrangement A Pericyciic Reaction (Section 20.6A) The Gaisen rearrangement transforms an allyl phenyl ether to an ortho-substituted phenol. The reaction takes place in a single step and involves the redistribution of six... 

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