STERIC HINDRANCE FACILITATED SYNTHESIS OF ENYNES AND THEIR INTRAMOLECULAR [4+2]CYCLOADDITION WITH ALKYNES

The palladium-catalyzed insertion of 1-alkynes into internal alkynes w hich are bent out of linearity by the interference with a peri or orth o substituent led to enynes regioselectively. The resulting enynes und ergo a new type of intramolecular thermal cycloaddition, which can be used for the annulation of an aryl ring onto naphthalene derivatives t o afford fluranthenes. The cyclization of (E)-1-(1-buten-3-ynyl)-8-eth ynylnaphthalene could also be performed in the presence of a Cu(I) cat alyst at room temperature.