40–48 hours, racemic starting material and >60% of >95% ee acylated product are recovered. Here, the unreacted starting material racemizes in situ via a dimeric enamine, resulting in a recovery of greater than 50% yield of the enantiopure acylated amine product. Chemoenzymatic dynamic kinetic resolutions There have been a number of reported procedures which take advantage of a chemical reagent/catalyst to perform racemization of the starting material and an enzyme to selectively react with one enantiomer, called chemoenzymatic dynamic kinetic resolutions. PSL-C was utilized along with a ruthenium catalyst (for racemization) to produce enantiopure (>95% ee) δ-hydroxylactones. More recently, secondary alcohols have been resolved by Bäckvall with yields up to 99% and ee's up to >99% utilizing CALB and a ruthenium racemization complex. A second type of chemoenzymatic dynamic kinetic resolution involves a π-allyl complex from an allylic acetate with palladium. Here, racemization occurs with loss of the acetate, forming a cationic complex with the transition metal center, as shown below. Palladium has been shown to facilitate this reaction, while ruthenium has been shown to affect a similar reaction, also shown below. Parallel kinetic resolution In parallel kinetic resolution (PKR), a racemic mixture reacts to form two non-enantiomeric products, often through completely different reaction pathways. With PKR, there is no tradeoff between conversion and ee, as the formed products are not enantiomers. One strategy for PKR is to remove the less reactive enantiomer (towards the desired chiral catalyst) from the reaction mixture by subjecting it to a second set of reaction conditions that preferentially react with it, ideally with an approximately equal reaction rate. Thus, both enantiomers are consumed in different pathways at equal rates. PKR experiments can be stereodivergent, regiodivergent, or structurally divergent. One of the most highly efficient PKR's reported to date was accomplished by Yoshito Kishi in 1998; CBS reduction of a racemic steroidal ketone resulted in stereoselective reduction, producing two diastereomers of >99% ee, as shown below. PKR have also been accomplished with the use of enzyme catalysts. Using the fungus Mortierella isabellina NRRL 1757, reduction of racemic β-ketonitriles affords two diastereomers, which can be separated and re-oxidized to give highly enantiopure β-ketonitriles. Highly synthetically useful parallel kinetic resolutions have truly yet to be discovered, however. A number of procedures have been discovered that give acceptable ee's and yields, but there are very few examples which give highly selective parallel kinetic resolution and not simply somewhat