CHAPTER 10: Question 6

 

2D Explanations

First note that the product contains two stereocentres, so there are four stereoisomers of this compound. The synthesis of one stereoisomer is shown in Scheme 10.9. The enantiomer of the product shown in Scheme 10.9 can be obtained by using the enantiomer of the diisopropyl tartrate shown in Scheme 10.9. This is because the diisopropyl tartrate is the only chiral species present at the start of the reaction, so the chirality of this species directly determines which enantiomer of the product is obtained.

The other two stereoisomers of the product will be diastereomeric to the pair of enantiomers discussed above, and to form them a starting material that is diastereomeric to the starting material shown in Scheme 10.9 is required. This can be achieved by using the Z- rather than the E-isomer of the alkene. Thus, reaction of the Z-isomer of the alkene with the enantiomer of diisopropyl tartrate shown in Scheme 10.9 will give a third stereoisomer of the product, and reaction of the Z-isomer of the alkene with the other enantiomer of diisopropyl tartrate to that shown in Scheme 10.9 will give the fourth stereoisomer.

The reagents needed to form the three stereoisomers not shown in Scheme 10.9 are shown in the schemes below.



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