Question

b) (10 points) The Puryna memungoment can be a pain to an organic chalet Hà NaOH a) Write a mechanism for the Payne rearrangement which accounts for all stercochemistry observed. b) When reacted with t-Bus (a bulky nucleophile), attack on one of these epoxides is slow, so we can get one major product. Please predict what product would be obtained showing all appropriate stereochemistry b) Explain why one of these cpoxides reacts much slower than the other in the reaction above with the bulky nucleophile o e ê

Answer 1

Mechanism of payne Reaza-cingement 419. NAOH ROHS OH - R mechanism:. R ei Nach OH = 9 Ron 16 10 → under basic condition, The H-From -OH "be gemoved to Foam gikoxide fon the neighbouaing aikoxide group attacks intramolecularly to make a neces, de 900 anged epoxy alcohol. This is called payne georzangement 10 electroche OH © Ans: Site (more deactive) 99. NOOH E-Buse. OH Both are 2 electrophilic CFast on S-LBU ® CSN2) oo (sloce? | Burt Site Cless deactive) ve Therefore direct addition is Slow R s-E-BU thorach r major product) → epoxide A gives a slow Reaction, opening of epoxide conith E-Buse.is SN 2 Reacton (attack of nucleophile. From Opposite direction) in A both the carbons of epoxide ade 20. Therefore dorect additron Of bulky E-Buse is hindered Hence the gate of deaction is slovo. epoxide has a 10 electrophilic site, there is less Steaic hinderance for attack of bulky E-Bus group. therefore it Jeacts faster.