Question

Q2B Compound 7 is reduced stereo-selectively via a Noyori asymmetric hydrogenation reaction. Reagents Reagents (R)-8 1) Taking the stereochemistry into account, suggest appropriate reagents (reagents 2) for this transformation (hint: analyse the absolute configuration of product (R)-8 absolute configuration). 2 marks 2) Using the mnemonic model for this transformation, show the stereodetermining step in this catalysis. Briefly explain your reasoning. 4 marks 3) Using the mnemonic model for this transformation, show why compound (S)-8 is not formed. Briefly explain your reasoning. 4 marks

Answer 1

Answers:

1) (R)BINAP-Ru

2) Find attached stereodetermining mechanism

H otMe MOH (R)-Ribo 5-BINAP] RUD o-I Ha (R)-BINAPRO BINAP Meo O Me Pro-Me C) [(R) BINAP] R Mc-o-H come OH i one . [[R) -BINAR R Te 01- 01

• The (R)BINAP-Ru methoxy  coordinated precatalyst gets hydride from H₂ and forms Ru-monhydride reaction intermediate while giving off Methanol.
• The Ru centre of the catalyst coordinates to oxygen atoms of the ester compound.
• Because of the R Chirality of the ligand R diastereomeric transition state is favoured. Ester gets proton and hydride transfers from the catalyst to the carbonyl carbon.
• The hydrogenated ester compound leaves the catalyst and solvent coordinate back to the catalyst.

3) Since the catalyst used is of the R form the above reaction mechanism to produce R form of the product is most favoured.

• The (R)BINAP-Ru methoxy  coordinated precatalyst gets hydride from H₂ and forms Ru-monhydride reaction intermediate while giving off Methanol.
• The Ru centre of the catalyst coordinates to oxygen atoms of the ester compound.
• Because of the R Chirality of the ligand R diastereomeric transition state is favoured. Ester gets proton and hydride transfers from the catalyst to the carbonyl carbon.
• The hydrogenated ester compound leaves the catalyst and solvent coordinate back to the catalyst.