Tungsten(0)‐ and Rhenium(I)‐Catalyzed Tandem Cyclization of Acetylenic Dienol Silyl Ethers Based on Geminal Carbo‐Functionalization of Alkynes

Tungsten(0)‐ and rhenium(I)‐catalyzed reactions of acetylenic dienol silyl ethers based on the concept of geminal carbo‐functionalization of alkynes are reported. Treatment of 3‐siloxy‐1,3‐diene‐7‐ynes with catalytic amounts of [W(CO) 6 ] or [ReCl(CO) 5 ] under photoirradiation conditions gives synthetically useful bicyclo[3.3.0]octane derivatives in good yields. Extremely high catalytic activity is noted for the rhenium(I) complex. The reaction has been extended to substrates containing a nitrogen atom in their tethers. In this case, two kinds of synthetically useful heterocyclic compounds—the 2‐azabicyclo[3.3.0]octane derivatives 9 and the monocyclic dihydropyrroles 10 , with allenyl substituents—are obtained, and selective preparation of either product can be achieved through the use of an appropriate combination of the nitrogen substituent and the type of the rhenium(I) catalyst. The 2‐azabicyclo[3.3.0]octane derivatives 9 are obtained selectively by carrying out treatment of NNs derivatives in the presence of [ReCl(CO) 4 (PPh 3 )], whereas the dihydropyrrole derivatives 10 are obtained by treatment of NMbs derivatives with [ReCl(CO) 5 ]/AgSbF 6 . Finally, we have applied this geminal carbo‐functionalization to one‐carbon‐elongated substrates containing NTs moieties in their tethers. Selective 5‐ exo cyclization is achieved in the presence of gold(I) or rhenium(I) catalysts, whereas 6‐ endo cyclization is observed on use of [W(CO) 6 ].