the starting material was 4-hydroxysalicylaldehyde
(Table 1, entry 8), O-acylation took place, giving 7-acetoxy-
3-acetamidocoumarin (5h) as the product.
The next step involved conversion of the acetamide to a
t-butyl carbamate. Burk and Allen’s one-pot protocol
was then employed to afford the Boc-protected 3-aminocoumarins
(6b–i) (Table 2). Under these conditions, the
acetoxy group in compound 5h was converted back to a
hydroxy group (Table 2, entry 8). For the most part, the
yields were high. As above, the yields of the products
with donor groups at the 7-position (Table 2, entries 6
and 8) were comparatively low.
Removal of the Boc-group using 15% TFA/CHCl3 then
afforded the 3-aminocoumarins (7b–i) in generally very
good yields (58–96%) (Table 3). In no case was any
3-hydroxycoumarin detected. Clearly, the use of a tbutoxycarbonyl
protecting group is crucial because it
can be removed under anhydrous conditions. The optimal
reaction times for preparing the desired 3-amino-