Acid catalyzed cyclodimerization of 2,2-bis(trifluoromethyl)-4-alkoxy-oxetanes and -thietanes. Synthesis of 2,2,6,6-tetrakis(trifluoromethyl)-4,8-dialkoxy-1,5-dioxocanes and 3,3,7,7-tetrakis(trifluoromethyl)-9-oxa-2,6-dithia-bicyclo[3.3.1]nonane

Treatment of 2,2-bis(trifluoromethyl)-4-R-oxetanes (R = C₂H₅O, n-C₃H₇O, n-C₄H₉O) with BF₃.OEt₂ in CH₂Cl₂ solvent results in spontaneous electrophilic [4 + 4] cyclodimerization with the formation of the corresponding 2,2,6,6-tetrakis(trifluoromethyl)-4,8-dialkoxy-1,5-dioxocanes, isolated in 31-42% yield. The structures of two products (R = C₂H₅O and n-C₃H₇O) were established by single crystal X-ray diffraction. The corresponding oxetane carrying the bulky t-C₄H₉O group has different reactivity towards BF₃.OEt₂, slowly producing a mixture of two acyclic, unsaturated products.Clean and spontaneous reaction with alcohols is another interesting transformation of oxetanes described in this paper. The reaction leads to high yield formation of the corresponding acetals (CF₃)₂C(OH)CH₂CH(OR)OR'.Structurally related 2,2-bis(trifluoromethyl)-4-R-thietanes (R = i-C₃H₇O, t-C₄H₉O and C₂H₅O) have different reactivity towards electrophiles. They are totally inert to the action of BF₃.OEt₂ and rapidly react with a protic acid (H₂SO₄) forming the same product, 3,3,7,7-tetrakis(trifluoromethyl)-9-oxa-2,6-dithia-bicyclo[3.3.1]nonane in 35-50% yield. The structure of this product was established by single crystal X-ray diffraction.