1- FLUOROADAMANTANE

Koch and Miller [12] reported that oxidation of 1-chloro- and 1-fluoroadamantane at a platinum anode in acetonitrile is a two-electron process leading to the formation of the corresponding M-(3-halo-l-adamantyl)acetamide in yields of 91 and 65%, respectively (Eq. 2) ... 

FLUORINATIONS WITH PYRIDINIUM POLYHYDROGEN FLUORIDE REAGENT 1-FLUOROADAMANTANE... 

Since 1-fluoroadamantane sublimes easily, the water bath should be controlled to about 32°, and the vacuum evaporation of the solvent limited to as short a time as possible. 

Adamantane (1) reacts with xenon difluoride in carbon disulfide at —15 to 0 C to form 1-fluoroadamantane (2) in 35% yield.14... 

Fluoroacetamide [640-19-7] M 77.1, m 108°. Crystd from chloroform. 1-Fluoroadamantane see 1-adamantyl fluoride. 

Recently Barton et al. (98) reported extremely selective high-yield reactions at —78°C in CFCl3 between fluorine and adamantane and substituted adamantanes. 1-Fluoroadamantane is produced in 84% yield from adamantane, and 3-fluoro-/V-trifluoroacetyl adamantane is produced from /V-trifluoro-acetyladamantane in 83% yield (98). In addition, Barton, Hesse and coworkers reported regioselective reactions of a number of steroids with yields ranging from 25 to 75% (99). Some of the selectivity in the steroids is rather remarkable and is thought to result from electrophyllic reactions that are strongly influenced by polar substituents on the molecules and by solvents (98,99) p. 73. Although the yields are very impressive in these reports, no information is provided on the conversion or the scale. 

Adcock and Kok have analysed the 19F chemical shifts of a range of 3-substituted 1-fluoroadamantane derivatives 62. The substituent chemical shift (19F SCS) can be factorized into polar field (pf f) and residual contributions (19F SCS - pf f)- A significant solvent-independent residual contribution is observed when R = SiMe3, and is attributed to homohyperconjugation70. 

The chemical shift differences observed for these 1-fluoro-l-methyl-f-butylcyclohexanes, the cis- and rrans-9-nuomdecalins, and for 1-fluoroadamantane provide insight regarding the significant influence of conformation upon fluorine chemical shifts in fluorocyclohexanes. The relative chemical shifts of these various cyclohexyl fluorides can be rationalized simply on the basis of what is commonly known as an anomeric effect. That is, a vicinal hydrogen that is rigidly anti to a fluorine substituent will exhibit an anomeric double-bond/no-bond... 

Analysis of the 19F NMR substituent chemical shifts134,135 (SCS) for a range of 3-substituted 1-fluoroadamantane derivatives 162 demonstrate the presence of significant residual contributions (19F SCS-rF.vF), when R = SiMe3 and SnMe3. 

Alkanes do not usually react with xenon difluoride at room temperature, while thermally initiated fluorinations of organic molecules have received much less attention than liquid-phase reactions. Zajc and Zupan16 have shown that several hydrocarbons react with xenon difluoride when heated to 95-120 °C. Reproducible results can be observed only when a teflon jacket is used in the stainless reactor with appropriate preconditioning. Cyclohexane is converted to fluorocyclohexane, while the reaction with -hexane gives three monofluoro-substituted products. Fluorination of adamantane results in the formation of four products, from whose distribution it is evident that the difference in the reactivity between the secondary and the tertiary carbon atom is much larger than the difference between the reactivities of the primary and secondary carbon atoms of hexane. Liquid-phase functionalization of a tertiary carbon atom is observed in reactions in carbon disulfide, where 1-fluoroadamantane is formed17. 

Fluoroadamantane (mp 259 260 "C) is obtained under similar conditions in an almost quantitative yield from l-(trimethylsiloxy)adamantane. ... 

Adamantyl fluoride (1-fluoroadamantane) [768-92-3] M 154.2, m 210-212 (dec), 259-260 (dec). Dissolve in Et20, dry over Na2S04 evaporate to dryness and sublime the residue at 90-100°/12mm. Recryst sublimate from MeOH, m 259-260 . [Zh Org Khim 30 1609 1965.] To remove 1-hydroxyadamantane impurity, dissolve in cyclohexane cool for many hours, filter off the hydroxyadamantane, and evaporate to dryness. Recrystallise the residue from pet ether at -77° and sublime in vacuum, m 210-212° dec (sealed tube). [/ Org Chem 30 789 1965.]... 

Adamantyltetrafluorophosphorane (23) cannot be prepared from the phos-phonyl difluoride (77) by treatment with sulphur tetrafluoride. Instead, it has been prepared in good yield by Lewis-acid-induced cleavage of 1-fluoroadamantane the first time this has been achieved with an alkyl fluoride. ... 

Bridgehead fluoroadamantanes. 1-Bromoadamantane is converted by anhydrous zinc fluoride in refluxing cyclohexane into 1-fluoroadamantane in 61% yield. However, the yield is sensitive to the heat treatment required to obtain anhydrous salt from the tetrahydrate and the reaction becomes increasingly slow as the number of bridgehead bromine atoms is increased. In this case the more expensive silver fluoride is used. Even 1,3,5,7-tetrabromoadamantane can be... 

Fluorination at saturated carbon. Hesse et al. have observed that adamantanc in the presence of radical inhibitors (.e.g., nitrobenzene) reacts with CF3OF to form 1-fluoroadamantane (75% yield). The same reaction can be carried out with Fa itself. This reaction is characterized by almost exclusive attack at a tertiary position, pronounced tendency to monosubstitution, and a marked polar effect on the rate (adamantane substituted at the 1-position by NHCOCF3 is much less reactive than adamantane). Thus the reaction is considered to involve direct electrophilic fluorination. 

This dichotomy is quite evident in the reaction of cydooctane with nitronium trifluoroacetate. The products obtained were cyclooctyl triflu-oroacetate, cyclooctyl nitrate and nitrocydooctane. Conversion of adaman-tane to 1-fluoroadamantane in 95% 3ueld on reaction with nitronium tetrafluoroborate in pyridine polyhydrogen fluoride indicates that formation of adamantyl cation by formal hydride abstraction is a significant alternative to the nitration-protodenitration pathway. 

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