# Can some one please explain alkyl shifts for me

Provide a mechanism for the following reaction. Include all intermediates, resonance structures, charges, and electron pushing arrows to obtain full credit.

I’m stuck with this problem. I got as far as step 2 of the mechanism. I know the double bond acts as a nucleophile and attacks one of the hydrogen on sulfuric acid thus creating its conjugated base $$\ce{HSO4-}$$ leaving a carbocation on carbon 1.

In previous problems I have done the carbocation will rearrange to form a more stable cation. I’m told it’s done by either a hydride shift (which I understand) or an alkyl shift. I’m having a hard time grasping the concept of a six-membered ring going into a five-membered ring. And essentially understanding why there is a shift.

• #1) In an analogy: Are you able to number non-H atoms in your starting material in a pattern like a shoelace (this time with definitive start and end), and may you place this on the product? Don't feel bad if you need to draw such numbering patterns for you, at the beginning you probably need multiple attempts to find your way through. #2) You probably recognize $\ce{H2SO4}$ as an acid, capable to donate protons. What could be sites in the organic molecule accepting protons -- even if only in an equilibrium? #3) Sketch how these new molecule could serve as starting materials. Sep 24 '19 at 20:41
• #4) Probably there are multiple pathways found; which one is more reasonable, than others? (It is not saying that the reaction definitively works this or that way, but finding what makes more sense.) This site won't provide you right on the sleeves the answer. But if you document what you already tried to tackle the question, it is easier to recognize where you need help. Sep 24 '19 at 20:43
• Thank you for you feedback. I was not clear with my question. Sep 24 '19 at 22:45
• I seriously question the product in this reaction. The carbon bearing two methoxy groups and one hydroxyl group is the intermediate in ester hydrolysis. Orthoesters are acceptable but not this 2/3-orthoester. Sep 25 '19 at 23:17
• @user55119 You are right, the targeted compound (the «2/3-orthoester») is unknown to Elsevier's Reaxys database; regardless if searched as drawn here, or allowing further than methox-substition as only $\ce{-C(OMe)2OH}$. Sep 27 '19 at 21:20