Otto-Kurt Extension

Chemistry Level 3

An extension to Teleanu Florin's problem .

( Pausinystalia johimbe )

The final compound is a diastereomer of Yohimban (the base chemical structure of various alkaloids in the Pausinystalia plant genera) and is synthesised using the following scheme:

The above compounds are heated in $Et_{3}N$ and generate an intermediate A . When A is reduced, a penta-cyclic compound is formed:

Let $\alpha$ be the mass of compound A and $\beta$ be the mass of the final product.

Calculate $\alpha -\beta$

BONUS

Determine configuration of all stereo-centres in the final product if the acyl chloride's chiral centre is in the R configuration.

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38 50 44 48

1 solution

Vitthal Yellambalse
Jan 30, 2017

In this reaction $Et_{3}N$ plays a duel role of a solvent and a base. The first step involves the abstraction of the sulfamide hydrogen and the subsequent nucleophillic attack on the acyl chloride. It doesn't attack the bromine atom as the $S_{N}2$ route is hindered and $S_{N}1$ cannot occur due to orbital interactions.

The next step starts from the realisation that the sulfamide is a hidden nucleophile and can attack the bromine atom in an $S_{N}2$ manner due to its close proximity. After the attack $Et_{3}N$ abstracts the hydrogen atom.

Now an intermolecular cyclo-addition occurs to generate the intermediate A :

It is clear that $\beta$ is 280 and from the above structure we see that $\alpha$ is 324. Hence the answer is $\boxed{44}$

Determining stereochemical configuration is left as an exercise for the reader.

Otto-Kurt Extension

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