Cycloalkyl fluorides

In going from a secondary to a tertiary cycloalkyl fluoride, one observes the usual deshielding effect as is exemplified by the isomeric 1 -lluoro-1 -mcthyl-4-t-butylcyclohcxancs. Of course, these two isomers exist essentially in the single conformation given, because of the presence of the 4-t-butyl substituent. 

Carbon-Fluorine Coupling Constants in Alkyl and Cycloalkyl Fluorides... 

The magnitude of carbon-fluorine coupling attenuates with coupling distance in alkyl and cycloalkyl fluorides, as shown in Tables 4.20(b) and 4.21. Analogously to vicinal proton-proton, carbon-proton and carbon-carbon coupling (Sections 3.2.2.4, 3.2.4.2), 37cf depends on the dihedral angle enclosed by the C—C—C —F connection, and Karplus cosine relations such as eq. (4.7) have been derived empirically [266] and theoretically [267],... 

To a mixture of cycloalkyl fluoride 17 (0.2 g, 0.5 mmol) and dicyclohexano-18-crown-6 (1 mmol) in toluene or diglyme, alkali metal [K or Na-K (44 56 w/w) alloy, 1 mmol] was added. The mixture was stirred at rt for 3 h under N2, followed by quenching with i-PrOH (1 mL). In some experiments. i-PrOH (0.5 mL) was added at the beginning of the reaction as a proton source. Cholestane (18) was isolated by TLC (silica gel). 

Scheme 2.53 Examples of the fluorination of alcohols with a,a-clifluoroalkylamines or a-fluroro-enamines. Synthesis of cycloalkyl fluorides, fluorosteroids, fluoroterpenes, and glycosyl fluorides with G-fluoroenamines [122, 123].

C. The Fluorosvlphonic Acid-Antimony Pentafluoride and Hydrogen Fluoride-Antimony Pentafluoride Solvent Systems Attempts to generate simple alkyl-, arylalkyl-, and cycloalkyl-carbonium ions in sulphuric acid or oleum solution generally result in... 

A number of cycloalkyl-, vinyl-, aryl-, and benzyllithium compounds (predominantly benzyl-lithiums) are converted into fluoro derivatives in good to excellent yields, e.g. formation of 4, 5, and 6 19 however, when this method was applied to the synthesisof 3-fluorobenzocyclobutene from the lithium salt a violent explosion occurred when the reaction mixture was warmed from — 70 C to room temperature.20 Various fluoro-substituted thiophenes 7 are obtained when the starting compounds (thiophene, 2-methylthiophene, etc.) arc transformed with al-kyllithium compounds to the corresponding lithium derivatives then fluorinated with perchloryl fluoride at 0 C.21 Potassium tricyanomethanidc is converted at —15 C in triglyme into tricyanofluoromethane in 81 % yield.22... 

Cycloalkyl and secondary alkyl bromides react with N02 BF4 in pyridinium poly(hydrogen fluoride) solution to yield /J-fluorinated compounds in moderate to good yields. In the case of the cyclic starting materials like 1-bromocyclohexane only trans-substituted products are formed (see Table 22). 

Various oligomers of fluorinated alkenes and cycloalkenes have been prepared by fluoride ion induced oligomerisation of various monomers (Sect. 5.3), and the chemistry of these systems provides some unique reactions. The oligomers of special interest here may be described as of types (95) or (96) (Scheme 59), i. e. systems with either four (95) or three (96) perfluoro-alkyl or -cycloalkyl groups attached to the double bond, whereas systems with two perfluoroalkyl groups attached, i. e. (97) and (98), have a chemistry more similar to fluorinated alkenes that may be derived from other sources. 

The synthesis of azo-compounds via condensation of perfluorinated w-nitrosoalkanecarboxylic acids or esters with amines was mentioned earlier [item (vi), p. 231]. An alternative method to the AtNHj-RfNO condensation for the preparation of azo-compounds of the type AtNiNRf (Rf = perfluoro-alkyl or -cycloalkyl) has now been discovered, viz. trapping of peifluoro-carbanions (from perfluoro-olefins + caesium or potassium fluoride) with arenediazonium salts (see Scheme 36). ... 

Diethylaminosulphur trifluroide converts cyclo-octanol into a mixture of cyclooctyl fluoride (70%) and ds-cyclo-octene (30%). Kinetic data suggests that there is considerable C—Br bond breaking in the transition state for abstraction of bromine from cycloalkyl bromides by phenyl radicals, and that anchimeric assistance by an adjacent bromine atom to bromine abstraction depends upon the accessibility of a trans-periplanar alignment of leaving and neighbouring groups. ... 

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