Question

5. Please identify X and Y in the reaction sequence below. ལམ་པ་མ་ཕམ་པ། ༤ 1)HBr 1) HBr ， Y 2) PPh3, then NaH

What is the mechanism behind this? (Especially on the NaH part)

Answer 1

kDetails of the mechanism:

12 and and Yin & y in the lity X fluus K5 reaction: @ppha 1) HBro 2) PPhy, then NaH Mechanism is as follows: bre @pphz PPh₂ ๕ app Ph ๕ pph C-Ph OL Expected Return

Step 1 and 2 is electrophillic addition reaction of HBr to alkene following Markownikov's rule.

Step 3 involves displacement of Br by PPh3 to form phosphonium ion.

Step 4: Here NaH works as a base and is used to abstract proton from $\alpha$ - position of PPh3 to generate a phosphorus ylide which can also exist in its other resonating form as shown in the mechanism.

Step 5: This is wittig reaction between a carbonyl compound and phosphorus ylide to generate alkene.