MECHANISM
In this reaction an acyl pyridium ion is formed which is the reactive species. Facile addition of the alcohol to the acyl pyridinium ion regenerates DMAP and, after loss of the oxonium proton to acetate, forms the desired product plus acetic acid which is scavenged by Et3N.
reaction—
|
|
wt/vol |
MW |
moles |
density |
equivs. |
yield |
|
I |
17.966 g |
442.65 |
0.0406 |
|
1.0 |
|
|
II |
19.10 mL |
102.09 |
0.2024 |
1.082 |
5.0 |
|
|
III |
22.60 mL |
101.19 |
0.1621 |
0.726 |
4.0 |
|
|
IV |
0.496 g |
122.17 |
0.0041 |
|
0.1 |
|
|
V |
400 mL |
– |
– |
|
|
|
|
VI |
18.440 g |
484.69 |
0.0380 |
|
|
(94%) |
Procedure: 1000 mL 1-neck flask, stirbar, septum, N2 inlet
Dissolved 17.966 g of alcohol I in 400 mL of dry CH2Cl2. Stirred at rt. Added 19.10 mL of Ac2O followed by 22.6 mL of Et3N and 0.469 g of DMAP. After 3h, quenched with sat. aq. NH4Cl. Extracted with CH2Cl2. The organic layer was dried over MgSO4, filtered and the solvent was removed by rotary evaporation. The product was isolated by flash chromatography on silica gel using 10:90 EtOAc-hexanes as eluant. The product was a clear, colorless oil.
[a]D +11.00 (c = 1.82, CH2Cl2).
