Oxindoles with Chiral Quarternary Carbon via Hetero-Claisen Chemistry

An area of chemistry I have found interesting for many years now is the use of sigmatropic rearrangements since they can result in high degree of chemo- and stereoselectivity.  A couple of years ago I reviewed a stimulating text about the Claisen rearrangement by M Hiersemann and U Nubbemeyer and was a little disappointed to note that there appeared to be very few examples of industrial application. Perhaps the chemistry below (A D Smith et al, Org Lett, 2009, 11, (17), 3858) will find application in due course since it appears to be straightforward, results in acceptable yield and chiral purities, works with a range of substitutions and the chiral unit is reported to be recoverable in reasonably good yield of about 80%.

An example of the application is given below:

The authors report about 9 examples with reaction yields 78-91% and ee’s 78-90%, although on recrystallisation some ee’s are significantly improved.  An interesting example of application is shown below.