Contingency and serendipity in the reactions of Fischer carbene complexes with conjugated triynes.

The first examples of reactions of Fischer carbene complexes with triynes are reported. The regioselectivity of the reaction of the two different alkyne functions in the symmetrical triyne depends on the nature of the substituent of the triyne. Bis-silyl-substituted triynes react at the central alkyne unit, whereas bis-aryl- and bis-alkyl-substituted triynes react at the end alkyne unit. The reaction of a Fischer carbene complex with a phenyl substituent also reacts with a bis-silyl-substituted triyne at the central alkyne unit but gives a furan product rather than the normal phenol product. It was also demonstrated that all three of the alkyne units in conjugated triynes could react in turn with a Fischer carbene complex to give access to trisquinones.