Organic Chemistry 1 · Carbocation rearrangements and ring expansions
Use a methyl shift to make 2-methoxy-2,3-dimethylbutane
Conditions: 3,3-Dimethylbut-1-ene → 2-methoxy-2,3-dimethylbutane
Draw this problem yourself
Drag from the electrons that move to where they go, or tap one and then the other. Every arrow is checked; Hint helps when you're stuck. No account needed.
The question
Which reagents convert 3,3-dimethylbut-1-ene into 2-methoxy-2,3-dimethylbutane?
Reveal the answer and explanation
Answer and explanation
Correct answer CH3OH, H2SO4 (cat.)
The free secondary cation undergoes the methyl shift before methanol captures the tertiary cation.
Not this one Hg(OAc)2, CH3OH; then NaBH4
The bridged mercurinium ion prevents the shift, giving unrearranged 2-methoxy-3,3-dimethylbutane.
Not this one BH3·THF; H2O2, NaOH; then NaH, CH3I
Hydroboration puts oxygen on the terminal carbon, giving 1-methoxy-3,3-dimethylbutane with no shift.
Not this one NaOCH3, CH3OH
Methoxide does not add to an unactivated alkene, so no reaction occurs.
Worked solution
The target has the methoxy group on a tertiary carbon of a rearranged skeleton, so the route must pass through a free carbocation. Catalytic H2SO4 in methanol protonates the alkene to a secondary cation, a methyl shifts to make it tertiary, and methanol traps it. Alkoxymercuration avoids free cations and gives the unrearranged ether instead.
What you'll practice
Plan reagents that convert 3,3-dimethylbut-1-ene into 2-methoxy-2,3-dimethylbutane by exploiting a carbocation methyl shift.
You just pushed every arrow of this one.
Every one of the 5349 Orgo 1 and Orgo 2 problems works like this: feedback on each arrow, hints when you're stuck, a no-hint quiz mode. Free with an account, no card.
Stuck on your own homework?
Snap it — first scan free, no sign-up
Scanning every week? Scan Standard: for about problems