Replacement of a carboxyl function by fluorine, fluorodecarboxylation, is a new process that can be accomplished by the reaction of alkanoic acids with xenon difluoride. Primary, tertiary, and benzylic acids perform best in the reaction, which is conducted at room temperature in methylene chloride or chloroform solution. A reaction mechanism is proposed in which the acid is initially converted to a fluoroxenon ester, RCO2XeF. The esters of the primary and secondary acids react by nucleophilic displacement by fluoride, as evidenced by incorporation of 18F− and no reactions common to free radicals or carbocations. The esters of the tertiary and benzylic acids react by converting to free radicals that can be further oxidized to carbocations. Thus incorporation of 18F− and racemization are observed with α-methoxy-α-trifluoromethylphenylacetic acid. Hydroxyl and amino functions inhibit the reaction. Aromatic and vinylic acids do not react.

The reaction between xenon difluoride and aliphatic carboxylic acids causes decarboxylation with replacement of the carboxyl group by fluorine.

5H))-furanone (7b) in 78% and 15% yields, respectively. 6b: colorless oil; MS m / e 218; IR (neat) 1765 cm-' (C=O). Anal. Calcd for C13H1403: C, 71.54; H, 6.47. Found: C, 71.50; H, 6.44. Hydrogenation of 6a. Into a solution of 6a (408 mg, 2.0 "01) in methanol (20 mL) was added Pd/C (5%, 100 mg), and the mixture was stirred for 18 h at room temperature under a hydrogen atmosphere. The catalyst was removed by filtration, and the filtrate was evaporated to give a mixture of diastereomers of 3,4-dihydro-5-methoxy-4-methyl-3-phenyl-2(5~-furanone @a): 406 mg; a colorless oil; IR (neat) 1775 cm-' (C==O). The 40()-MHz 'H NMR spectrum showed four sets of signals: b 0.69,0.72, 1.05, and 1.15 for methyl protons and 6 3.52, 3.49, 3.48, and 3.56 for methoxy protons. The isomer ratio (82:l:l) was determined from the peak areas of the methoxy protons. The resonances for major component are as follows: 6 0.69 (d, 3 H, Me, J = 7.3 Hz), 2.85 (dqd, 1 H, CHMe,J = 9.8, 7.3,and 5.4 Hz), 3.52 (s, 3 H, OMe), 3.87 (d, 1 H, CHPh,J = 9.8 Hz), 5.37 (d, 1 H, OCHO, J = 5.4 Hz), 7.18-7.33 (m, 5 H, Ph). Carbonylation of la in Ethanol in the Presence of Rh4-(CO),, and Various Bases (Table I). Into a 30-mL glass tube containing a Teflon-coated magnetic stirring bar were added l a (0.18 g, 1.0 mmol), Rh,(C0)12 (19 mg, 0.025 mmol), a base (1.0 mmol), and ethanol (15 mL), and the tube was placed into a 50-mL stainless-steel autoclave. The autoclave was sealed, flushed twice with carbon monoxide, pressurized to 40 kg/cm2, and heated with stirring at 125 OC for 6 h. The reaction mixture was analyzed by GC. The results are shown in Table I.Alcoholysis of 3b. A mixture of compound 3b (100 mg, 0.36 mmol) and Na2C03 (106 mg, 1.0 mmol) in ethanol (15 mL) was stirred at 150 "C for 6 h under 50 kg/cm2 of carbon monoxide in the same way described above. GC analysis of the reaction mixture indicated the presence of 5 (81 mg) and 3b (14 mg). Registry No. la,Reactions of CF30X (X = C1, F) with a variety of simple alkenes were carried out to compare the regio-and stereoselectivity of the additions to carbon-carbon double bonds. The observed addition products with CF30Cl are consistent with an electrophilic syn addition. With CF30F the observed products indicate a different regioselectivity and low stereoselectivity, consistent with a free-radical addition.

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