Aromatic Homo-Nazarov-Type Cyclization of Benzonorcaradienes: Stereoselective Synthesis of Hydrochrysenes

Abstract

Formal homo-Nazarov cyclization of benzonorcaradienes produced by intramolecular hydroarylation of arylated alkynylcyclopropanes promoted by TfOH has been described, providing stereoselective access to highly substituted hydrochrysenes. An unprecedented 1,2-acyl migration occurred for the 2-heteroaroyl substrates, thus giving the same products as their 3heteroaroyl analogs. Moreover, these products could be readily oxidized by air to fully π-conjugated chrysenes after decarboxylation.

Intramolecular 1,2-Aroyl Migration in Spiro Donor–Acceptor Cyclopropanes: Formation of 1,4-Naphthoquinones and 1-Naphthols as Ring-Expansion Products

“…Among the various rearrangement reactions of DACs, the Cloke–Wilson rearrangements of cyclopropyl ketone to dihydrofuran, cyclopropyl imine to pyrroline, cyclopropyl ester to γ-butyrolactone, cyclopropyl amide to γ-butyrolactam, and other rearrangements such as nitrocyclopropane to isooxazoline- N -oxide involve the formation of new C–O or C–N bonds in the products (1,3-migration of carbon atom). Similarly, the vinylcyclopropane to cyclopentene rearrangement, homo-Nazarov rearrangement of cyclopropyl vinyl/aryl ketones to cyclohexenones/α-tetralones, and other rearrangements involve the formation of a new C–C bond (1,3- or 1,4-migration). However, a rearrangement involving the breaking and reformation of C–C bond between vicinal ring carbons (1,2-migration) has been seldom observed in DAC chemistry. , Few years back, we reported that aroyl-substituted DACs 1 upon treatment with AlCl 3 undergo ring-opening, fragmentation (cleavage of C–C bond), and 1,2-aroyl migration to vicinal carbon (reformation of C–C bond) to give γ-ketoesters 2 (which undergo further cyclization to yield 2-pyrones under the reaction conditions) (Scheme , eq 1) .…”