GaCl₃-Mediated Cascade [2 + 4]-Cycloaddition/[4 + 2]-Annulation of Donor–Acceptor Cyclopropanes with Conjugated Dienes: Strategy for the Construction of Benzobicyclo[3.3.1]nonane Skeleton

Abstract

Structurally important benzobicyclo[3.3.1]­nonane derivatives were synthesized by a gallium trichloride mediated reaction of readily available donor–acceptor cyclopropanes (DACs) with 1,3-dienes as a one-pot cascade ionic [2 + 4]-cycloaddition/Friedel–Crafts-type cyclization process. At the first stage, DACs act as sources of formal gallium 1,2-zwitterionic complexes to give 6-benzylcyclohex-3-ene-1,1-dicarboxylates that are converted under certain conditions in the presence of GaCl3 to give benzobicyclo[3.3.1]­nonanes in 30–74% yields. The process is tolerant of varying substituents at different positions of the main framework. Further, potentially useful modifications of benzobicyclo[3.3.1]­nonane derivatives are demonstrated. 2-Cyclopropylbutadiene reacts with DAC at higher temperature more deeply with cleavage of three-membered rings in both cyclopropane substrates, and twofold alkylation of the Ph-substituent at ortho- and meta-positions, that leads to a 1,2,7,8,9,10-hexahydro-6H-7,10a-methanocycloocta­[cd]­indene skeleton. Cyclopropane-1,1-diesters containing a bulky substituent in the ester group react with isoprene in a different way to give bicyclic lactones containing a 2-oxabicyclo[2.2.2]­octan-3-one moiety.

Gallium(III)- and Indium(III)-Containing Ionic Liquids as Highly Active Catalysts in Organic Synthesis

“…Compounds containing gallium and indium, especially halides and salts, are known as substitutes for standard Lewis acids, and their use has been proven in countless chemical transformations in the field of organic chemistry. Due to remarkable catalytic properties resulting from high acidity, they can be used successfully in various chemical processes, such as Friedel–Craft reactions [ 15 , 16 , 17 ], cycloaddition reactions [ 18 , 19 , 20 , 21 , 22 ], olefin metathesis [ 23 ], various coupling reactions [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ] and many others [ 12 , 32 , 33 , 34 , 35 , 36 , 37 ]. Although many applications of these compounds have already been explored, their usefulness extends in connection with the possibility of incorporating gallium and indium into structures of ILs with unique properties.…”

The Cloke–Wilson rearrangement of aroyl-substituted donor–acceptor cylopropanes containing arylethyl donors

“…Donor–acceptor (D–A) cyclopropanes have emerged as one of the leading building blocks in modern organic synthesis owing to the richness of their reactivity. 1 A multitude of cyclic and acyclic products has been accessed through Lewis acid mediated rearrangement, 2 ring-opening 3 and (3 + n ) annulation 4 reactions of D–A cyclopropanes. Apart from the regular D–A substituents at the vicinal positions, the introduction of an additional substituent at the third position of the cyclopropane ring leads to intriguing outcomes in the reactions of D–A cyclopropanes, as exemplified by aroyl- and nitro-substituted D–A cyclopropanes reported from our laboratory.…”