Allenyl Ketones The Cycloisomerization to Furans

A more detailed view of the selectivities (Table 12.5) reveals a selective formation of the 2,4-disubstituted furan with the copper(I) catalysts (entries 1 and 2), a low 

TABLE 12.3. Different Catalysts for the Formation of 2-Benzopyrylinm Salts 

The individual results are listed in Table 12.6. Copper halides are not active for this conversion (entries 1-3) only the copper triflates deliver the product, with copper (II) affording a better yield (entries 4 and 5). All silver salts are active, and again the triflates are superior and in dichloromethane even operate at room temperature 

TABLE 12.4. Cycloisomerization or Cycloisomerization/Dimerization of Allenyl Ketones (R1 = Me) 

Entry Catalyst Conversion (%) Ratio Monomer Dimer 

---