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

Abstract

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.