West Virginia University Department of Chemistry rganic Division April 4 th, 2012 Cumulative Exam # 378 X. Michael Shi rganic Cumulative Examination #378 ame Question # 1 (29 points): Question # 2 (34 points): Question # 3 (40 points): Total (103 points):
Question 1. Some fundamental terms involved carbene chemistry a) Give an example of Setter reaction and draw detailed electron-pushing mechanism. (5 points) b) Draw the detailed structures of Grubbs I, Grubbs II, Hoveyda-Grubbs catalysts (6 points) c) Schrock entered the metathesis field in 1979 and extending the work on Tantalum and Tungsten complexes. The Tantalum complex suffered from catalyst turnover as the reaction shown below. Provide the product (2 points) Cl Cp Ta Cl pentane, 25 o C The Tungsten complexes became Schrock catalyst, which was commercialized starting in 1990. Provide the detailed structure of this catalyst (2 points). In addition, Schrock further developed this system to asymmetric catalyst in 1993. Provide the chiral Schrock catalyst (2 points). 1
d) Another major area in carbene catalysis was the application of dirhodium complexes for the activation of stabilized carbene. Provide the product for the following reaction. (2 point) 2 dirhodium catalyst CbZ DCE, 60 o C Provide detailed electron-pushing mechanism. ote: for the metal catalysis, there are several different argument regarding the mechanism, you will receive full credit if you can provide any of the reasonable plausible mechanism regarding this transformation with all details provided. (4 points) e) Two more terms: 1) draw examples of Breslow intermediate (2 point); 2) Draw examples of Fisher carbene and Schrock carbene, CLEARLY explain the difference (4points) 2
Question 2. Carbene catalysis a) For the following reaction first reported by Jeff Bode. H + Ts 10% Detailed electron-pushing reaction mechanism (6 points); structure of DBU (1 point), Mes (1 point). Mes Cl - 15% DBU, 0.1 M EtAc, rt H Ts b) Draw the detailed electron pushing for the following reaction reported by Tom Rovis (6 points) H 3 C Br H + BnH Et3, Tol H 3 C Br Bn 3
c) For the following reaction reported by Hoveyda. Provide detailed electron-pushing reaction mechanism (6 points). Predict the stereochemistry of the product (> 98:2 d.r.). Draw the transition-state that account for the formation of the r corresponding stereochemistry (4 points). + CH 2.5% Cy BF - 4 + Cy 2.5% at-bu, B 2 (pin) 2, THF, rt H B d) Draw the detailed electron pushing mechanism for the following catalytic kinetic resolution (8 points). What is the other major product (2 points) Mes 0.5 eq H + H 1 eq + H 10% 10% Cl 4 - Mes Mes 4
Question 3. Carbene metal complexes/catalysts a) In 2010, Huw Davis reported the reaction carbene annulation with Indole. Me 2 C H 2 C 2 Me A Rh 2 (S-DSP) 4 Rh 2 (S-DSP) 4 1) Draw detailed electron-pushing mechanism for the formation of A (5 points) 2) What is the structure of B (2 points). Wish identical di-rh catalyst, predict the stereochemistry of B (2 points) B b) Recently (ACIE, 2012, 2939), Rai-Shung Liu reported the following reaction. Provided the detailed electron pushing mechanism (5 points). Draw the structure of IPr (2 points) + + - IPrAuCl/AgTf 2 5
c) In 2011, Jianbo Wang reported the following reaction 2 Me + H 2 2.5% Pd 2 (dba) 3 K 3 P 4 1.5 eq. C 1atm Me, 60 o C H 1) Structure of dba? (2 points) structure of Pd 2 (dba) 3? (2 points) 2) Mechanism? (6 points) Me d) Professor Peter Zhang developed a porphyrin-based Co(II) catalysts that has been used in nitrene and carbene chemistry. 1) See the simplified Co-P catalyst. Provide electron counting of Co (2 points). 2) Draw the d-electrons distribution. Hint: different energy of the d-orbitals (2 points) 3) Provide the detailed electron pushing for the following reaction (5 points) Co 3 2 S H Co cat S H H 6
e) Valery Fokin reported the following transformation. Draw the detailed electron pushing mechanism (5 points) H + Tf 2 (1 eq) CH 1% Rh 2 (Ac) 4 CH 2 Cl 2 t-bu t-bu The end. 7