Rearrangements hydride

Bromine trifluoride is used to selectively substitute fluorine for bromine in brominated alkanes and esters. The reactions are carried out by gradual addition of bromine trifluoride to a solution of the substrate in CFC-113 or CFC-112 at 10-20nC. The bromine-fluorine exchange in mono-bromohaloalkanes is nonstereoselective and accompanied, in some eases, by skeletal rearrangements, hydride shifts, and halogen migrations. All three fluorine atoms in bromine trifluoride are involved in the fluorination reaction. Chlorine atoms in the substrate molecules remain intact.109... 

A-13. Rearrangement (hydride migration) occurs to form a more stable carbocation. 

Since in electron spectroscopy the time scale of the measured ionization processes is on the order of 10 16 sec, definite ionic species are characterized, regardless on their possible intra- and intermolecular interactions (e. g., Wagner-Meerwein rearrangements, hydride shifts, proton exchange, etc.). Thus, electron spectroscopy gives an undisputible, direct answer to the long debated question of the non-classical nature of the norbornyl cation independent of any possible equilibration process. 

Creating or removing unsaturation on the ligand can initiate a ct-tt rearrangement. Hydride abstraction and protonation reactions are perhaps the best-elucidated examples. 

Efficient preparation of 2,3-diarylbenzo[ft]thiophenes (475) is accomplished in two ways starting from thioisatins (474) (Scheme 98) <83TL3381>, A series of reactions, that is, Grignard reaction, pinacol rearrangement, hydride reduction, and acid-catalyzed rearrangement, converts (474) to thiophenes (475). Another series of reactions, Friedel-Crafts reaction, hydride reduction, and acid-catalyzed rearrangement, also convert (474) to (475). 

STEPS 5-9 OF FIGURE 23.16 CARBOCATION REARRANGEMENTS Once the tetracyclic carbon skeleton of lanosterol has been formed, a series of carbocation rearrangements occur (Section 7.10). The first rearrangement, hydride... 

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