Anionotropic complexes

A review on anionotropic 1,2-rearrangements of borate complexes evidences the most important factors that are responsible for which group migrates, by showing a broad spectrum of reactions involving borate complexes.17... 

Organoboranes can be used for the synthesis of various organic compounds containing an amino group . The most common procedures involve the reaction of organoboranes with azides, with hydroxylamine derivatives, or with chloroamines. All amination reactions proceed via intermediate formation of a borate complex followed by anionotropic rearrangement to form the new C—N bond (Equation (21)). 

The structural closeness of 1-boraadamantane (5) and 1-azaadamantane (113) induced the attempts to convert (5) into (113). The first reported synthesis has been carried out according to the following synthetic scheme. Treatment of (5) with A,iV-dichloroamines leads to the formation of an intramolecular complex compound (114). A second anionotropic migration in (114) gives rise to compound (115) standard oxidation of the latter provides 3-alkyl-3-azabicyclo[3.3.1]nonanes (116) (Scheme 42) <8UOM(220)l>. 

A more convenient procedure for the synthesis of (113) from (5) was later elaborated <9UOM(4l2)l>. It is based on the intramolecular version of the reaction of organoboranes with organic azides. The THF complex of 1-boraadamantane (5a) is treated with iodine in the presence of an excess of sodium azide. The iodine atom in the intermediately formed borabicycle (118) undergoes an easy nucleophilic substitution by azide ions. The subsequent anionotropic rearrangement in the borabicyclic azide (119) leads (after the oxidation of the reaction mixture) to aminoalcohol (120), which is smoothly converted to 1-azaadamantane (113). The yield of (113) in this synthesis is 40-45% based on (5a), or 20-22% based on triallylborane (Scheme 44). 

Organopalladium derivatives containing Pd(II) can serve as sources of carbocationic species. Both alkene-Pd Tr-complexes and oxypalladated intermediates in the Wacker oxidation reactions can therefore generate carbocationic intermediates, which may then undergo anionotropic rearrangements (Scheme 6). In fact, it is rather remaikable that, despite the well-known involvanent of alkene-Pd Tr-complexes and oxypalladated intermediates, the Wacker-type oxidation of alkenes is relatively free from various possible rearrangement reactions. 

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