Overman: Limitations 2-propyl 18-24% under Sncl conditions 2-propyl 30% under SnCl4 conditions 。ms retro-Aldol LOTS % Unsaturation or heteroatoms at the B or y positions of the acetal initiator are not tolerated in these reactions. JACS, 1988, 110, 2248 Overman: Synthesis of trans-Kumausyne trans-Kumausyne 4:1 regioselectivity 1. H2, Pd-c *CHO OTES 32C-093/22999:40AM 4cs,1991,113537Overman: Synthesis of trans-Kumausyne JACS, 1991, 113, 5378 O AcO Et Br trans-Kumausyne OH OH O H H O OBn O H H OBn O BnOCH O 2CHO RSO3H, rt 69% m-CPBA 72% 4:1 regioselectivity 1. H2, Pd-C, 88% 2. Swern, 100% O H H O O Me TMS BF3•OEt2 -78 °C → rt 73% 1. 2. TBSCl O H H O O Et O OTBS HO Et OTBS H O DIBAL -78 °C 97% CHO Overman: Limitations JACS, 1988, 110, 2248 O Cl Me (-)-Laurenyne Cl TMS O O 2 2-propyl 2-propenyl 18-24% under SnCl4 conditions no reaction under a variety of conditions O TMS Cl OSitBuMe2 OEt 2-propyl 2-propenyl 30% under SnCl4 conditions gives only acetal cleavage O TMS Cl OR Et EtO X X = Br X = SMe X = OAc X = Me R = TBS R = TBS R = TBS R = Me decomposition, acetal cleavage O TMS Cl OTBS EtO EtO Me O TMS Cl OTBS EtO Me + O TMS Cl OTBS 2 O OTBS Me • Unsaturation or heteroatoms at the β or γ positions of the acetal initiator are not tolerated in these reactions. 24% retro-Aldol Cl 32C-09 3/22/99 9:40 AM