Poly(phosphoric acid) (PPA)-Promoted 5-exo-Cyclization of Iminium Ions Generated In Situ: A Facile Access to Functionalized Indene Derivatives

Abstract

A metal-free Brønsted acid promoted two-component reaction between cinnamaldehydes and sulfonamides is described. This cascade process provides a simple and atom-economical alternative synthesis of a range of functionalized indenes from easily available starting materials. The resulting N-indenylsulfonamides were readily converted into the corresponding indenylenamines or indanones.

Transition‐Metal‐Free Synthesis of 1‐Indanone Skeleton: A Brief Update

“…Fan et al devised a novel polyphosphoric acid (PPA)‐catalyzed approach to the synthesis of functionalized indene derivatives 32 through condensation of substituted cinnamaldehydes 31 with sulphonamides 21 [36] . Both electron‐rich and electron‐deficient cinnamaldehydes are suitable as substrates (Scheme 10).…”

Synthesis of 3-aminoindenes and cis-1-aminoindanes by Zn(OTf)2-catalyzed cyclization of o-alkynylbenzaldehydes with tertiary alkyl primary amines

“…At this stage, the isomerization of the double bond is anticipated to follow, eventually furnishing 3-aminoindenes. 4 a ,7 On the other hand, the full reduction of the iminoindenone intermediates would afford 1-aminoindanes. Herein, we disclose our preliminary study on the synthesis of 3-aminoindenes through Zn( ii )-catalyzed cascade reaction between o -alkynylbenzaldehydes and tertiary alkyl primary amines, which affords 3-aminoindenes with complementary substitution pattern.…”