they rapidly afford the thiol and selenol esters ( 5) and ( 6) , respectively, in good yields (Table 2).
The enol esters ( 4 b), ( 4 c), and ( 4 f) of cc-hydroxy carboxylic' acids are exceptions; their transformation into (5 b), (5 c), and (Sf), respectively, is best accomplished with thiophenol in the presence of 10mol X, of 4-dimethyIamin0pyridine~'~.
The alkali salt of N,N-dimethylacetoacetamide accompanying (5) or ( 6) is easily removed by filtration (or-after neutralization-N,N-dimethylacetoacetamide is removed by washing with water). Activation with (1) and acylation to give ( 5) and ( 6) can be carried out as a one-pot reaction without isolation of (4)[91.
Procedure (Z)-N,N-Dimethyl-3-(3c1,7c1,12u-trihydroxy-5~-cholanoy1oxy)crotonamide ( 4 j ) : A solution of cholic acid ( 2 j ) (4.08g, 10mmol) in anhydrous THF (20ml) is added to a stirred solution of (1) (1.16g, 10.5mmol) in anhydrous THF (30ml) at -50°C with exclusion of moisture. After 20min at -50°C, the mixture is allowed to warm to room temperature and then evaporated down in vacuo. Recrystallization of the residue from chloroform/n-hexane gives 5.08 g (98 %) of colorless crystals, m. p. 166-1 67 "C.
S-Cyclohexanethiol ester of 12-hydroxystearic acid ( 5 g ) : A solution of Li cyclohexanethiolate (1.28 g, 10.5 mmol) in anhydrous THF (20ml) is added to a solution of ( 4 9 ) prepared from (1) (10.5mmol) and ( 2 9 ) (10mmol) in anhydrous THF (50 ml). After 1 h at O' C, precipitated Li N,N-dimethylacetoacetamide is filtered off and the filtrate washed with water after addition ofethyl acetate(1Oml). After drying over MgS04 and removal of solvent, the residue is dissolved in methylene chloride and filtered over silica gel (Kieselgel 60, Merck).
The oil crystallizes on concentration to give 3.14g (79 %) of colorless crystals, m.p. 37--38°C.