The deviating behavior of thiols in nucleophilic trapping reactions of chromiumcarbonyl phenyl complex substituted propargyl cation

The (phenyl)Cr(CO)3-complex substituted propargyl cation 4 significantly deviates in the chemoselectivity of the nucleophilic attack of thiols from the previously reported planar chiral ortho-substituted arene complexes and furnishes allenyl thioethers 5. This peculiar behavior can be rationalized assuming a subsequent base catalyzed propargyl–allenyl isomerization in acidic medium (!). An X-ray structure analysis of allenyl thioether 5c recrystallized from acetonitrile over weeks reveals that the [2+2] cyclodimer 10 has been formed. Thiolate adds to 5c to give a single diastereomer of the allyl compound 15 in good yield.