A substrate-dependent reaction of 1-aryl-2-alkyl-1,2-diketones with 2-aroyl-1-chlorocyclopropanecarboxylates: selective access to 2',5'-dicyclopropoxy-1,1':4',1''-teraryls and pentafulvenes.

An interesting substrate-controlled one-pot approach to highly substituted 2',5'-dicyclopropoxy-1,1':4',1''-teraryls and 6-hydroxypentafulvenes involving various 1,2-diketones and 2-aroyl-1-chlorocyclopropanecarboxylates as 3C Michael acceptors triggered by Cs2CO3 has been developed. We noticed that 1,2-diketones play a decisive role in this reaction to determine the product's selectivity. For example, aryl rings having electron-poor functionalities at the para and meta-positions of 1,2-diketones led to 2,5-diarylhydroquinones selectively via a cyclodimerization/double oxa-Michael process with highly strained cyclopropenes. However, when 1-naphthyl/electron-donating aryl/ortho-aryl-substituted 1,2-diketones were chosen, the Michael-initiated ring expansion reaction (C-C and CC bonds) took place under the same conditions that gave the corresponding pentafulvenes predominately. Moreover, this reaction has several imperative features such as good to high diastereoselectivities, wide substrate scope, good functional group tolerance, transition metal-free process, etc.