SYNTHESIS OF FLUOROALKYL METHYL THIOETHERS BY FORMAL ADDITION OF METHANESULFENYL FLUORIDE TO ALKENES

The electrophilic anti-1,2-addition of the elements of methanesulfenyl fluoride to carbon-carbon double bonds by a one-pot reaction of dimethyl(methylthio)sulfonium tetrafluoroborate and triethylamine trishydrofluoride with various types of alkenes is used for the synthesis of beta-fluoroalkyl methyl thioethers. This reaction is stereospecific: starting from cis-cycloalkenes (1) trans-1-fluoro-2-(methylthio)cycloalkanes (2) are formed, while trans-cyclododecene (3) gives the cis product 4 everytime in good yields. With unsymmetrical alkenes these reactions proceed regioselectively to produce Markovnikov-oriented fluoro thioethers. With 2,6-norbornadiene (26) exclusive exo attack on one double bond and subsequent transannular participation of the second pi-bond gives rise to two isomeric 3,5-disubstituted nortricyclanes, 28 and 29, while starting from the medium-sized cis,cis-1,5-cyclooctadiene (10) no transannular pi-participation is observed: the trans-1,2-addition product to one of the two double bonds in 11 is isolated. In contrast, in the reaction of the monoepoxide 30 of this diene in addition to the simple 1,2-adduct 31 a transannular oxygen participation occurs producing three oxa bicyclic compounds 32-34. The oxidation of 1-fluoro-2-(methylthio)cyclooctane (2a) by sodium periodate yields the expected mixture of two diastereomeric 1-fluoro-2-(methylsulfinyl)cyclooctanes (36) which on pyrolysis give 3-fluorocyclooctene (37).