Group Meeting Problems
October 11, 2006
Part A.
OH
O
OH
O
O
1.
How many products can form from this cyclization? Please show the stereochemistry of
the spiroketal.
2.
Please draw all chair-chair conformers of the products, and point out the most stable one.
Part B. Provide a mechanism for the following proline-catalyzed intramolecular aldol reaction
(List et al. Angew. Chem. Int. Ed, 2003, 42, 2785. Include a three-dimensional representation of
the transition state that rationalizes the diastereo and enantioselection of the process base on
the enamine intermediate mechanism.
CO2H
N
H
OHC
OH
OHC
CHO
10 mol%
CH2Cl2
12 hr, rt
Note: There are four possible products.
10 : 1 dr,
99% ee,
95% yield