Question

Listed below are four reaction schemes (Scheme A-D), as well as a synthetic target. Select which scheme will give the desired product with the greatest selectivity, and briefly describe why (both need to be included for full credit): Scheme A Me LDA -78 °C Ph -78°C to 25°C 25°C Scheme B Me LDA 25 °C Ph 25°C to -78 °C -78 °C Scheme C Me LDA Ph H -78 °C -78 °C Scheme D . Me LDA -78 °C 25 °C Phí H -78°C to 25 °C to -78 °C -78 °C OLI O Me Target Ph TTT Arial 3 (12p T

Answer 1

The correct scheme to get target molecule Oli re is scheme Phi Target Oli Club CHz -78°C CH3 내 +LiGN + Ph H сиз LDA base CLDA) => CH₃ ph ketone Benrad. Strong & Bulky kinetic -dehyde Esterble at -28°C) -78°C Here, the ketone reacts with LDA which is strong & brallky base. So LOA abstracts, proton from less sterrically hindered side of gooms Kinetic enolate which is stable at - 78 °C. If we increase the temperture from - 78 °C to 25°C then kinetic enolcete isomerizes into thomody anamically stable enolate & we would 'n't get the target molecule. So, we have to maintain temp at -78 °C to keep kinetic enolate stable which whill then react with al benzaldehyde to give at -28° C to give Target molecule. so, the correct scheme is © Target molecule