Synthesis of Substituted Indenes through Iron‐Catalyzed Annulation of Benzylic Alcohols with Alkynes

Abstract

A convenient and efficient method for the synthesis of polysubstituted indenes has been developed by the ironA C H T U N G T R E N N U N G (III) trichloride-catalyzed tandem mono-and dibenzylation/cyclization reactions of benzylic alcohols with alkynes. This method is featured with the easily available starting materials, cheap catalyst, simple manipulation and mild conditions.

Iron Catalysis in Organic Synthesis

“…222 Thus, benzylic alcohols were treated with arylalkynes in 1,2-dichloroethane at room temperature in the presence of 5 mol % of the catalyst to give indenes in high yields (eq a). Electron-deficient alkynes and electron-rich benzylic alcohols easily undergo a second benzylation.…”

Frustrated Lewis Pair‐Catalyzed Cycloisomerization of 1,5‐Enynes via a 5‐endo‐dig Cyclization/Protodeborylation Sequence

“…In analogy,t he stoichiometric reaction of 1,6-enynes with B(C 6 F 5 ) 3 (1)w as recently reported leading to peripheral B(C 6 F 5 ) 2 -substituted five-membered carbo-and heterocycles. Thed istance between C8 and C9 is 1.355(2) , which is typical for an indene CÀC double bond (reported value 1.350 ), [13] supporting the Scheme 1. So far, only the B(C 6 F 5 ) 3 -catalyzed hydroamination of alkynes was realized through protodeborylation of the transiently formed ammonium borate.…”

“…[14] The 11 Bc hemical shift (d = 68.9 ppm) and the crystal structure corroborated the formation of at rigonal planar boron center (sum of angles 3598 8). Thed istance between C8 and C9 is 1.355 (2) , which is typical for an indene CÀC double bond (reported value 1.350 ), [13] supporting the Scheme 1. Catalyzed cycloisomerization of an 1,5-enyne.…”

Taming a Vinyl Cation with a Simple Al(OTf)3 Catalyst To Promote C−C Bond Cleavage

“…[9] In addition, aF riedel-Crafts (F-C) reactiona tt he nucleophilic substituents m-position could yield indene 5 (pathway c). [10,11] Ultimately,t he studies presented here shall providea nswers to the followingk ey questions, regarding the fate of the vinyl cation: 1) Why is the rearranged reaction product 3 formed selectively at the expanse of the directc yclization product 4 and the indene 5? 2) Whati st he exact nature of the 1,3-aryl shift and is it really cation-driven?…”