Synthesis of Polysubstituted 2-Iodoindenes via Iodonium-Induced Cyclization of Arylallenes

Abstract

A new chemoselective iodocarbocyclization of allenyl arenes was developed leading to the formation of 2-iodoindenes. In acetonitrile or nitromethane, electrophilic sources of iodine cations react selectively with the C2-C3 double bond of 1-arylallenes to give, after anti nucleophilic attack of the aromatic ring, 2-iodoindene products in high yields. Variations of the allenic skeletons revealed the high 5-endo selectivity and some competitive pathways of cyclization. Postfunctionalization reactions of the carbon-iodine bond, via Pd- and Cu-cross-couplings, gave rise to substituted indenes in good to excellent yields.

Synthesis and Functionalization of Allenes by Direct Pd‐Catalyzed Organolithium Cross‐Coupling

“…Furthermore, diversification of the synthesized allenes was also carried out. Te trasubstituted allenes 3b and 3e were converted into iodoindenes 8a,b in high yields (Scheme 7b), [30] providing,in this way,a na ppealing scaffold present in intermediates and structures with potential biological activity. [31] We also exploited the versatility of Cu catalyzed hydroboration of unsaturated bonds on trisubstituted allene 5b.…”

Catalytic asymmetric synthesis of chiral trisubstituted heteroaromatic allenes from 1,3-enynes

“…In addition, we also showed that the quinoline-substituted allene products 3a and 3d underwent NIS-initiated cyclization to generate the corresponding 2-iodo-pyrrolo[1,2-a]quinolones in good yields (Fig. 6b, NIS = N-iodosuccinimide) 61 . This copper-catalyzed asymmetric allenylation was utilized for the modification of complex molecules.…”

A Gold(I)‐Catalyzed Domino Coupling of Alcohols with Allenes Enables the Synthesis of Highly Substituted Indenes

“…Among the many methods reported for the synthesis of these compounds, one of the most important approaches is based on intramolecular Friedel–Crafts‐type reactions –. In a recent example, Toullec and co‐workers reported the N ‐iodosuccinimide(NIS)‐induced cyclization of allenes leading to substituted 2‐iodoindenes (Scheme a), which can then be further functionalized.…”