Table 1.
Triazolium catalyzed annulations of enals and alpha-hydroxyenones.a
 | |||||
|---|---|---|---|---|---|
| entry | R1 = | R2 = | % yieldb | 4:5:6c | % eed |
| 1 (a) | Ph | CO2Et (3a) | 95 (65) | 7e:2:1 | 99;88;99 |
| 2 (b) | p-MeOC6H4 | CO2Et (3a) | 90 (60) | 6:2:1 | 99 |
| 3 (c) | p-BrC6H4 | CO2Et (3a) | 91 (62) | 6:2f:1 | 99 |
| 4 (d) | p-CF3C6H4 | CO2Et (3a) | 89 (35) | 2:1:2 | 99 |
| 5 (e) | 1-naphthyl | CO2Et (3a) | (45) | nd | 99 |
| 6 (f) | 2-furyl | CO2Et (3a) | (40) | nd | 99 |
| 7 (g) | Ph | p-BrC6H4 (3b) | 73 (50) | –:3f:1f | –;93;99 |
| 8 (h) | Ph | p-CF3C6H4 (3c) | 91 (71) | –:4:1 | –;92;99 |
a
See Supporting Information for reaction details.
b
Total isolated yields of lactone products; yields of the major product in parenthesis
c
Determined by 1H NMR analysis of unpurified reaction mixtures.
d
Enantiomeric excesses of 4,5,6 as determined by SFC analysis on chiral columns. The ee of the minor products in entries 2–7 were not determined.
e
Structure determined by X-ray analysis of the corresponding methyl ester.
f
Structure determined by X-ray analysis.