Example 2 Degree of substitution of alkylating agent OR RBr COoT COOT COoT no solvent C3H7Br more sterically hindered 73 27 so harder mainly C-alkylation
Example 2 Degree of substitution of alkylating agent:
Example 3 OA Me K, CO3/TBAB OAc Aco- CH CN 十 Aco Aco →Br r. t Aco c CO,Et CO,Et K2CO3/TBAB CH3CN t EtO,C OAc OAc OAc Aco c Aco Aco Aco Me Aco Aco 62% R T Li et al. Synth. Commun. 1997, 27 (8),1351-1357
Example 3 AcO O AcO AcO OAc Br + Me CO2Et O K2CO3 / TBAB CH3CN r. t. AcO O AcO AcO OAc Me CO2Et O K2CO3 / TBAB CH3CN r. t. AcO O AcO AcO OAc Me EtO2C O + AcO O AcO AcO OAc OH + AcO O AcO AcO OAc 62% R. T. Li et al. Synth. Commun. 1997, 27(8), 1351-1357
2.区域选择性( Regioselectivity 区域选择性受热力学控制和动力学控制的反应条件影响 很大 热力学控制条件下主要生成取代基较多的烯醇; 动力学控制条件下主要生成取代基较少的烯醇 Example 1 LDA OTMS OTMS (MSCI OTMS quench) 84% 7%0 kinetic enolate Et3N TMSCI 13% 58% DMF,△ 60h thermodynamic enolate
2. 区域选择性（Regioselectivity) 区域选择性受热力学控制和动力学控制的反应条件影响 很大. 热力学控制条件下主要生成取代基较多的烯醇; 动力学控制条件下主要生成取代基较少的烯醇; Example 1
Example 2 CH CH3 Ba ase Control Selectivity LDA(0°C,THF) KHMDS(-78°C) Ph3CL(-78°C) 10 potassium bases not ---- Ph3CK(-78.C) enolate generation Ph3CLi thermodynamic NaH Ph3 CK
Example 2
3.立体选择性( Steroselectivity) Two issues: i site of deprotonation ii. geometry of enolate formed Z-enolate(Zusammen) CH R CH3 OM trans E-enolate(Entgegen) R CH3 烯醇化合物的立体选择性形成,将为不对 称合成提供平台
3. 立体选择性（Steroselectivity) 烯醇化合物的立体选择性形成, 将为不对 称合成提供平台