Reactions of 1,3-Diphenyl Cyclopentadiene with α-Aryldiazo Ketones to Enable C-H Insertions versus [4 + 2]-Cycloadditions via Au Catalyst and P(C 6 F 5 ) 3 Additive, Respectively.

Two distinct reaction chemoselectivities were reported for the reactions of α-aryldiazo ketone with 1,3-diphenylcyclopentadiene using gold catalyst and phosphine additives, respectively. In the presence of gold catalyst, α-aryldiazo ketone forms gold carbenes initially that are trapped with this 1,3-disubstituted cyclopentadiene to afford C-H insertion products. In the presence of P(C 6 F 5 ) 3 additive, α-aryldiazo ketone forms diarylketenes initially at elevated temperature, which are further stabilized by P(C 6 F 5 ) 3 to secure their entity before proceeding to unprecedented [4C + 2C] cycloadditions.