The syntheses of (±)-dasycarpidone, (±)-3-epi-dasycarpidone, (±)-uleine and (±)-3-epi-uleine

Abstract

The syntheses of the racemic forms of the indole alkaloids dasycarpidone (2b), 3-epi-dasycarpidone (2c), uleine (2a), and 3-epi-uleine (2d) together with that of 3-de-ethyldascarpidone (2e) are described. The key step in the approach involved the isomerisation of an indol-2-yl 1,2,5,6-tetrahydro-4-pyridyl ketone to an indol-2-yl 1,4,5,6-tetrahydro-4-pyridyl ketone (not isolated). This in turn in reacting as a cyclic enamine provided, by protonation an electrophilic centre for eventual closure to the indole β-position.