Question

1. Propose reagents and conditions for the following multistep syntheses. You may use any reagents necessary. Be sure to draw all isolable intermediates.

Answer 1

For this reaction, we will use two step synthesis. The answer also needs you to draw the isolable intermediates

Step 1: Bromination

The bromine will be substituted at Meta position due to Meta directing tendency of -CHO group.

си Feb О= 0

Step 2: Reduction using NaBH₄. The aldehyde will be reduced to alcohol

_{ои С Nabi}

Step 3: Converting alcohol to chloroalkane by PCl₅

Step 4: Conversion to Phosphorus Ylide

Chr- S- & + ppha/Bulißes-ch=eph,

Step 5: Wittig reaction and addition of Cyclohexanone

1 - - Си =

Here, all the products formed in intermediate steps are isolable intermediates. This method has been chosen because in the last step Cyclohexanone is easily available compound. Otherwise, one could have also achieved this conversion in two steps by using Bromocyclohexane along with PPh₃ and BuLi i.e. by Wittig reaction in the step 2 itself.

For that mechanism, Step 1 will remain as it is and step 2 will be,

Bas -cho Buli Isolable L Intermediate PPhy