SolutionsFacial control (asymmetric synthesis)
Exercise 1
How many stereoisomers can form in the aldol addition of the enolate of 3-pentanone to (R)-2-methylbutanal? How many if the aldehyde is racemic?
Two new stereocentres are created (C2 and C3 of the aldol) and that of the aldehyde is retained: with enantiomerically pure aldehyde there are 2 × 2 = 4 possible diastereomers (syn or anti, and in each case attack on one face or the other). If the aldehyde is racemic its enantiomers form as well: 8 stereoisomers.