Efficient synthetic methods that avoid multistep processes have become a prevalent objective to modern organic reaction development. We have discovered a novel isomerization of alkynyl hemi-ketals using phosphine catalysts that yields cyclic enones as its product. The enone products from the new reaction are isomeric to products we had prepared using triethylamine as the isomerization catalyst. Specifically, the enones prepared in the phosphine mediated isomerization contain an exocyclic alkene in contrast to the oxepinones from the triethylamine mediated reaction. The enones from the phosphine isomerization, based on their structure, can undergo subsequent reactions. Most notably, the enones undergo a rapid [4+2] cycloaddition in situ that gives spiro-ketal products in a one-pot process. The tandem isomerization-cycloaddition process allowed access to a diverse collection of spiro-ketals from relatively simple starting materials. The new reaction should find application in the rapid preparation of natural product like molecules.

Dimerization of alkynyl hemi-ketals to form novel spiro-ketals

243rd National Meeting (2012)

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