in You are on the right track in trying to form an alkene intermediate, first by

Question

in You are on the right track in trying to form an alkene intermediate, first by converting n the alcohol to a good leaving group, then by carrying out a base-promoted elimination. However, hydroxide ion will preferentially attack the methylene hydrogen at carbon 22 and form the more stable alkene 3-methyl-2-pentene, which would give a tertiary alcohol (3-methyl-3-pentanol, the starting materia upon hydration according to the Markovnikov rule, or a secondary alcohol (3-methyl-2-pentanol) upon hydroboration-oxidation 1) TsCl, pyridine NaOH OH NaBH4 OH 4) H202, NaOH, H20 4 (conc.) CHaO BHalTHF

Explanation / Answer

1) TsCl, pyridine

2) (CH3)3CO-

3) BH3/THF

4) H2O2, NaOH, H2O

Explanation: Reaction of alcohol with TsCl, pyridine produces tosylate as product. t-BuOK is a strong base which gives elimination reaction and produces less substituted alkene as product. Hydroboration - oxidation of alkene with BH3, THF and H2O2, NaOH, H2O produces less substituted alcohol as product.

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