CHAPTER 10: Question 3
2D Explanations
Since compound A is an aldehyde, it will react with hydrazine 10.11
to give a hydrazone in exactly the same way as any other aldehyde. In this
case however, since both 10.11 and A contain a stereocentre the
products (and the transition states) obtained from the two enantiomers
of A will be diastereomers of one another and hence of different energies
as shown by the green and magenta curves in the reaction pathway / energy
diagram below. However, both diastereomers of this product
will react with LDA to form the same anion (analogous to 10.13)
since the stereocentre adjacent to the C=O is destroyed during this step.
From this point on, the reaction pathway is identical to that described
in detail in question 1, and a single enantiomerically pure product is
obtained by reaction from the less hindered face of the anion. The structure
of the product is also shown below. Note that it does not matter which
enantiomer of A is used (or whether the racemate of A was used), the same
product will be obtained in each case since the stereocentre of A is destroyed
before the stereocentre of the product is created.
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