The Divergent Cascade Reactions of Arylalkynols with Homopropargylic Amines or Electron-Deficient Olefins: Access to the Spiro-Isobenzofuran-b-pyrroloquinolines or Bridged-Isobenzofuran Polycycles

Abstract

Two divergent cascade reactions of arylalkynols with homopropargylic amines or electron-deficient olefins were developed to synthesize the spiro-isobenzofuran- b-pyrroloquinolines or bridged-isobenzofuran heterocycles in good yields, respectively. One reaction actually involved intramolecular 5- endo-dig hydroamination cyclization-protonation of homopropargylic amines to give cycloiminium ions and intramolecular 5- exo-dig hydroalkoxylation cyclization of arylalkynols to generate isobenzofuran with exocyclic double bond, followed by the nontypical Povarov-type reaction in the presence of PtCl/FeCl cocatalysts. The other underwent intramolecular hydroalkoxylation cycloisomerization of alkynols with the subsequent normal [4 + 2] cycoaddition with dienophiles. Herein, the arylalkynols acted as both "masked" electron-rich olefins and "masked" electron-rich dienes.

The Povarov Reaction: A Versatile Method to Synthesize Tetrahydroquinolines, Quinolines and Julolidines

“…described by the use of bovine pancreas -chemotrypsin in aqueous acetonitrile 86 with a strong preference towards the trans diastereoisomers, whereas other enzymes such as papain, lipases, and amylases failed to provide the THQ. Concerning the reaction medium, polar solvents such as acetonitrile 34,37,41,45,47,51,54 and alcohols 53,65,87,88 were the most typical, but not a requirement since apolar solvents including dichloromethane, 35,74,89 dichloroethane 28,60,90 and toluene 78,91,92 were also well represented in the literature. Fluorinated alcohols, such as hexafluoroisopropanol (HFIP) 71 and trifluoroethanol (TFE) 50,93 can be employed to dissolve reagents that are insoluble in the most common solvents, 71 or can even act as the catalyst itself, thereby removing the requirement for the addition of acids.…”

Transition Metal‐Catalyzed Hydroalkoxylation of Alkynes: An Overview

“…Chemistry-A European Journal bicyclic scaffolds 147 by the usage of 5 mol % PtI 2 (Scheme 59). [64] In general, diastereoselectivity depends upon the dienophile. 5-membered dienophile furnished the desired cyclo-adduct with poor diastereoselectivity, while 6-membered dienophile afforded a single diastereomer.…”

“…Finally, the Povarov-type reaction took place between Int-L and Int-L1 to give polycyclic spiro-fused heterocycles 111 in good yield, albeit with poor diastereoselectivity (Scheme 60). [65] Platinum catalyzed multicomponent cascade reaction for the stereoselective synthesis of THF-fused spiro-quinolines was reported by Barluenga and co-workers (Scheme 61). [66] The method involved the reaction of aniline 151, aldehyde 152, and alkynol 153 with 5 mol % of [PtMe 2 (cod)] and 1 equivalent of HBF 4 to furnish THF-fused spiro-quinolines 154.…”

Substituent‐Controlled Divergent Cascade Cycloaddition Reactions of Chalcones and Arylalkynols: Access to Spiroketals and Oxa‐Bridged Fused Heterocycles

“…A number of cycloaddition reactions of Int1 have been reported, [3] but to our knowledge, there have been only a few reports of cycloadditions of Int2. [4] The lack of examples of the latter may be due to the predominance of competitive side reactions of pre-formed Int1.…”