Overman: Ring-Enlarging THF annulations RCHO.H 48-76% MeCHo sncl4,-70→-23 P 75-93% JAcs,1991,1135365 Overman: Ring-Enlarging THF annulations JAcs,1991,113.5365 32C-053/22999:30AMOverman: Ring-Enlarging THF annulations JACS, 1991, 113, 5365 O R H H O RCHO, H+ -H2O O ( )n R + OH OH ( )n OH -H+ ( )n OH OH O O R1 O R1 O R1CHO 52-85 % SnCl4, -70 °C, 1 h 48-76% OH OH O O Me SnCl4, -70 → -23 °C 75-93% MeCHO O Me O R2 R2 R3 R4 R3 R4 R2 R3 R4 Overman: Ring-Enlarging THF annulations JACS, 1991, 113, 5365 OH O O RCHO RSO3H OH O R + HO O OH R + O HO + O OH R + O O O O R R R R 32C-05 3/22/99 9:30 AM