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 = C(2)H(5)O, n-C(3)H(7)O, n-C(4)H(9)O) with BF(3)·OEt(2) in CH(2)Cl(2) 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 = C(2)H(5)O and n-C(3)H(7)O) were established by single crystal X-ray diffraction. The corresponding oxetane carrying the bulky t-C(4)H(9)O group has different reactivity towards BF(3)·OEt(2), 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 (CF(3))(2)C(OH)CH(2)CH(OR)OR′. Structurally related 2,2-bis(trifluoromethyl)-4-R-thietanes (R = i-C(3)H(7)O, t-C(4)H(9)O and C(2)H(5)O) have different reactivity towards electrophiles. They are totally inert to the action of BF(3)·OEt(2) and rapidly react with a protic acid (H(2)SO(4)) 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.