The crude earthworm extract catalysed aza-Diels-Alder
reactions for the synthesis of isoquinuclidine derivatives
Isoquinuclidine (azabicyclo[2.2.2]octane) has received considerable
attention due to their presence in numerous complex
natural products and pharmaceuticals. The crude earthworm extract could catalyse three-component aza-Diels-Alder reactions
for the synthesis of isoquinuclidine derivatives (Fig. 7). The
reactions of aromatic aldehydes, aromatic amines and cyclohexenone
in MeCN/H2O gave corresponding isoquinuclidines in
excellent yields of 86–99%, and all reactions afforded the endo
isomers as the major products with endo/exo ratio ranged from
68:32 to 65:35 (Table 6, entries 1–5). In the absence of the crude
earthworm extract, only a trace amount of product was observed
(Table 6, entry 6), indicating that the crude earthworm extract
indeed catalysed the aza-Diels-Alder reaction. Unfortunately,
there was no obvious enantiomeric excess of the products observed
by the chiral HPLC analysis.