The addition of indole and methyl indole at both high and ambient pressures
to a series of Michael accepters under the influence of ytterbium triflate
was investigated. Under ambient pressure the more reactive and less steric
ally hindered electrophiles gave the expected 3-alkylated indoles in good t
o excellent yields. The more problematic Michael accepters were subjected t
o pressures of 13 kbar. In all cases a dramatic reduction in reaction time
and a significant improvement in yields was observed. In the cases involvin
g 3-methylcyclohex-2-en-1-one, a by-product was formed and was characterize
d by single crystal X-ray diffraction. alpha,beta-Unsaturated ketones gave
the best yields. Enals tended to polymerize while enoates proved to be much
too unreactive. A particularly reactive malonate derived ester and beta-ni
trostyrene gave good yields at ambient pressures.