Tunable Arylative Cyclization of 1,6-Enynes Triggered by Rhodium(III)-Catalyzed C–H Activation

Two
tunable arylative cyclizations of cyclohexadienone-containing
1,6-enynes are reported via rhodium­(III)-catalyzed C–H activation
of O-substituted N-hydroxybenzamides. The use of
different O substituents, i.e. O-Piv and O-Me, on the directing group allows the formation of either
tetracyclic isoquinolones through an Ⓝ-Michael addition process
or hydrobenzofurans through a Ⓒ-Michael addition process. Mechanistic
investigations of these two cascade reactions clearly indicated that
the C–H bond cleavage process was involved in the turnover-limiting
step. Furthermore, the cyclization products could be subjected to
various transformations for elaborating the pharmaceutically and synthetically
valuable potential. This is the first example of a rhodium­(III)-catalyzed
arylative cyclization reaction of 1,6-enynes, and the results extend
the application realm of Cp*RhIII-catalyzed C–H
activation cascade reactions.