Efficient Synthesis of Octahydrophenanthrene Derivatives with Mild Cascade Reactions of Isochromenylium Tetrafluoroborates and Bifunctional Styrenes

Abstract

A highly efficient catalyst-free cascade reaction of air-stable isochromenylium tetrafluoroborates and bifunctional styrenes containing a 1,3-diketone moiety has been developed, affording the corresponding single diastereomeric ocatahydrophenanthrene derivatives (21 examples, up to 86% yield). A cascade process of [4 + 2]-cyclization and subsequent intramolecular nucleophilic addition is proposed to generate the three new C-C bonds diastereoselectively in the reactions.

Asymmetric reactions involving isobenzopyrylium ion intermediates

“…The reported reactions included 1,2-nucleophilic addition, [4+2] cycloaddition, [3+2] cycloaddition and various cascade reactions. [37][38][39][40][41][42][43][44] The asymmetric transformations of isobenzopyrylium ions have been less explored. 45 This may be because the planar 10 π-electron aromatic structure of the isobenzopyrylium ion lacks an obvious coordination site for a chiral catalyst which is often crucial for achieving high stereoselectivity.…”

Convenient One-Step Synthesis of Benzo[c]phenanthridines by Three-Component Reactions of Isochromenylium Tetrafluoroborates and Stilbenes in Acetonitrile

“…Our recent investigations of isochromenylium tetrafluoroborates (ICTBs), , a class of air-stable reactive organic salts having nonclassical Hückel aromaticity, have revealed that they were able to smoothly react with either nucleophiles at the C-1 position − or electron-rich olefins via [4 + 2]-cycloaddition pathways − under mild metal-free conditions. In addition, three-component reactions of ICTBs, enols (in situ derived from aliphatic aldehydes), and nitriles/aldehydes provided various amino- and hydroxyl-functionalized tetrahydronaphthalenes and dihydronaphthalenes .…”