Adamantane halogenation

The synthesis begins with the halogenation of adamantane (74) with bromine to give 76 or chlorine and AlClg to give 75. The four bridgehead positions... 

Acyclic cationic systems, chalcogen-halogen compounds, 35 299-301 Acylarsonic acids, 44 217 Acyldiazenido complexes, mechanisms of formation, 27 223-225 Acylium cation, 9 231, 241-243 Acylphosphonic acids, 44 217 Acylsilane, hydrolysis, 42 173 Adamantane... 

Diluted fluorine acts on bromo- and iodoadamantanes 1 forming the corresponding fiuoroadamantanes 3. The reaction goes well in several inert solvents particularly in trichloro-fluoromethane. It appears that the initial attack of the fluorine is on the halogen, followed by formation of the very stable adamantane cation 2 which then collapses to the fluorinated products 3.45... 

The mass spectra of a variety of 1- and 3-substituted homoadamantanes have been analyzed and compared 3SS). Analyses of the infrared spectra of alkyl substituted adamantanes 3S6) and analyses of the microwave spectra of 1-halogen substituted adamantanes 357) are also available. 

Table 1. Regioselectivity for functionalization of adamantane using halogen and carbon-centered radicals as the abstracting species.

For electrophilic and more bulky radicals, for example CnHal2n+i, selectivity increases dramatically. Whereas the selectivity for the radical chlorination (Table 1, entry 7) and bromination (Table 1, entry 8) of adamantane with Hal2 in CC14 is only approximately 5, for chlorinations with CC14 (Table 1, entries 9 and 10) and brominations with BrCCl3 (Table 1, entry 11) the selectivity increases to 21.5-27. Halogenations under metal-catalyzed GIF conditions (Table 1, entry 12) or in the presence of dioxirane (Table 1, entry 13) are less selective, because of the participation of oxygen-centered (GIF) or methyl (DMD) radicals. 

Conceptually similar a,a -annulations of ketone enamines have also been carried out with electrophilic alkenes containing a reactive allylic halogen, such as ethyl a-bromo-methylacrylate or dimethyl y-bromomesaconate318-320 (Scheme 156). An elegant one-pot synthesis of the adamantane ring system involving sequential double Stork and Dieckmann reactions has been developed by Stetter and Thomas321 (Scheme 157). Reaction of the bis-enamine 154 with ethyl a-bromomethylacrylate leads to the pentacy-clic system 155322 (Scheme 158). 

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