Evidence for prins-Pinacol mechanism nCle. CH2Cl2 >95% 78°c→-23°c om MacMillan Seminar. 1996 Examples of Stereoselective THF Formation hcHO 32C-033/1899951PM from MacEWan Seminar. 1996O Me O Ph Me Me Me O Me Me Ph Me O Me O O O Ph - Cl4SnO O Ph - Cl4SnO Ph - Cl4SnO - Cl4SnO O Ph Ph O O Ph O Evidence for Prins-Pinacol Mechanism from MacMillan Seminar, 1996 + + + + SnCl4, CH2Cl2 -78 °C → -23 °C >95% ee enantiopure racemic Prins [3,3] fast pinacol aldol O Me O Me Me O Me HO Me OH Me O O Me O Me O Me Me Me Me Me Me Me O Me Me O Me Me O Me Ph Examples of Stereoselective THF Formation SnCl4, CH2Cl2 -70 → -23 °C 82% 7:1 anti:syn BF3•OEt2 (E)-CH=CHPhCHO CH2Cl2, -55 °C 97% SnCl4, CH2Cl2 -70 → -23 °C 82% anti syn from MacMillan Seminar, 1996 32C-03 3/18/99 9:51 PM