Reduction of 4- tert -Butylcyclohexanone

In the first semester majors’ organic laboratory course at Miami, students work on a class project in which individual students contribute data to establish the diastereoselectivity of three different methods of reduction of 4-tert-butylcyclohexanone: NaBH4/EtOH, lithium tri-sec-butylborohydride (L-Selectride)/THF, and Al(isoPrO)3/isoPrOH (Meerwein-Pondorff-Verley or MPV reduction). 1H NMR analysis of the crude product mixtures provides a convenient method to establish the cis/trans isomer ratio of the product 4-tert-butylcyclohexanols. Reduction with NaBH4 leads predominately to the trans-isomer ((88 ± 3)% trans), L-Selectride yields predominately the cis-isomer ((92 ± 1)% cis), while MPV reduction leads to an equilibrium mixture containing (23 ± 4)% cis-isomer. After individual students report their stereoselectivity results on one of the three methods, the instructor compiles and averages the data, and reports it back to the students. The students write a formal report on the project in which the issues of diastereoselectivity and thermodynamic vs. kinetic control of a product mixture are addressed.