Dolbier HW Solutions 204

Dolbier HW Solutions 204 - The only practical method is 1...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
Next, convert the p -toluenesulfonate to the desired azide by an S N 2 reaction. ( j ) This problem is carried out in exactly the same way as the preceding one, except that the nucleophile in the second step is HS 2 . 8.31 ( a ) The two possible combinations of alkyl bromide and alkoxide ion that might yield tert -butyl methyl ether are 1. 2. We choose the f rst approach because it is an S N 2 reaction on the unhindered substrate, methyl bromide. The second approach requires an S N 2 reaction on a hindered tertiary alkyl halide, a very poor choice. Indeed, we would expect that the reaction of methoxide ion with tert -butyl bromide could not give any ether at all but would proceed entirely by E2 elimination: ( b ) Again, the better alternative is to choose the less hindered alkyl halide to permit substitution to predominate over elimination. An attempt to prepare this compound by the reaction gave cyclopentyl methyl ether in only 24% yield. Cyclopentene was isolated in 31% yield. ( c ) A 2,2-dimethylpropyl halide is too sterically hindered to be a good candidate for this synthesis.
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: The only practical method is 1 Potassium 2,2-dimethylpropoxide (CH 3 ) 3 CCH 2 OK Bromoethane CH 3 CH 2 Br Ethyl 2,2-dimethylpropyl ether (CH 3 ) 3 CCH 2 OCH 2 CH 3 1 Chlorocyclopentane CH 3 ONa Sodium methoxide Cl Cyclopentyl methyl ether OCH 3 OK 1 Potassium cyclopentoxide CH 3 Br Methyl bromide OCH 3 Cyclopentyl methyl ether fast CH 3 O 2 1 (CH 3 ) 3 CBr Methanol CH 3 OH 1 2-Methylpropene CH 2 C(CH 3 ) 2 slow Methoxide ion CH 3 O 2 1 tert-Butyl bromide (CH 3 ) 3 CBr tert-Butyl methyl ether (CH 3 ) 3 COCH 3 fast Methyl bromide CH 3 Br 1 tert-Butoxide ion (CH 3 ) 3 CO 2 tert-Butyl methyl ether (CH 3 ) 3 COCH 3 ( R )-sec-Butyl p-toluenesulfonate C OS O O CH 3 H CH 3 CH 3 CH 2 NaSH HS H CH 3 CH 2 CH 3 C ( S )-2-Butanethiol C OH H CH 3 CH 3 CH 2 ( R )-sec-Butyl alcohol p-toluenesulfonyl chloride pyridine ( R )-sec-Butyl p-toluenesulfonate C OS O O CH 3 H CH 3 CH 3 CH 2 NaN 3 N 3 H CH 3 CH 2 CH 3 C ( S )-sec-Butyl azide 198 NUCLEOPHILIC SUBSTITUTION...
View Full Document

Ask a homework question - tutors are online