Q.60.

Question

Question: Identify A in the following reaction sequence and draw a mechanism for the conversion of A to B. B has been converted to (S,S)-reboxetine, an antidepressant marketed outside the United States.

Step-by-Step Solution

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Answer

Answer

1Step 1: Asymmetric Epoxidation

Asymmetric oxidation of alkene will create two new chiral centers and two new functional groups simultaneously. Examples shown for asymmetric oxidation were the products of the laboratory of Prof. Bary Sharpless.

2Step 2: Example for asymmetric epoxidation

An example for Sharpless asymmetric epoxidation is shown below:

Example for asymmetric epoxidation

3Step 3: Identification of A

When (E)-phenylprop-2-en-1-ol is treated with Sharpless reagent and (-) DET, the product obtained is ((2R,3R)-3-phenyloxiran-2-yl)methanol. Therefore the structure of A is,

Representation of A

4Step 4: Mechanism for the conversion of A to B

The compound ((2R,3R)-3-phenyloxiran-2-yl)methanol reacts with 2-ethoxyphenol to give the product (2R,3S)-3-(2-methoxyphenoxy)-3-phenylpropane-1,2-diol. The mechanism of the reaction taking place is as represented below:

Mechanism for conversion of A to B

Q.59.

Q.61.

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