Question

13. (4 pts) Which of the following Newman projection represents the confirmation prior to B-hydrogen elimination of HA during a Heck reaction? Ph Ph Hex Ph H3C YNH Нас- Нусун Ph не POLX H. POLX H POLX POLX 14. (4 pts) If you determine the rate limiting step of your catalytic cycle is the oxidative addition when Pd(PCys) is used, which ligand would you chose to replace PCys so the reaction rate increases? a. PPh b. P(OPh)3 c. P(t-Bu); d. PCyPh2 15. (4 pts) Draw the major product for the following reaction, including the stereoselectivity relative to the CH3 group on the ring. CHE HC Ot-Bu M OCH IH PPT POOR o tol 0-101 bol CH, totes NBU OAc, DMF, 115 °C

Answer 1

13) The Newman conformation b represents the conformation prior to β hydrogen elimination of H_a during Heck reaction. As the β hydrogen with respect to Pd in Heck reaction is eliminated via syn elimination. As in the conformer a the H_b is syn to Pd so the H_a elimination is not possible, in c H_a is in gauch position and in d it is in anti position so in this three cases the β elimination is not possible in syn manner but in b as the H_a is in syn position of Pd so syn elimination is possible.