Question

1. The following transformations cannot be performed in one step. Provide a sequence of reactions to convert the "starting material" to the "product." Show all the reagents and synthetic intermediates. You can use any additional carbon sources if needed, but you must use the starting material given.

Answer 1

Given bromo compound on heating with alcoholic KOH undergoes dehydrobromination to form alkene shown in the scheme below. Reaction of this alkene with bromine water gives desired bromohydrin compound. Mechanism of bromohydrin formation involves first formation of bromonium ion followed by nucleophilic attack by water and subsequent loss of proton.

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Br2, H20 Alcoholic KOH но Heat Br Вг Mechanism: Br-Br Br "ОН Br - Н-О, -Br HH Но Br Н Br

Given dibromo compound on reaction with two equivalents of strong base such as sodium amide gives corresponding alkyne. Partial reduction of this alkyne using Lindlar catalyst gives desired cis olefin.

Br NaNH2 Pd, BaSO4 Lindlar catalyst (2 equivalents) Br H2 gas Mechanism: NH2 Br NH2 Br Lindlar catalyst Hydrogenation