ChemInform Abstract: Catalytic Regioselective Synthesis of Structurally Diverse Indene Derivatives from N‐Benzylic Sulfonamides and Disubstituted Alkynes.

Abstract

FeCl3‐catalyzed cleavage of the carbon—nitrogen bond in N‐benzylic sulfinamides produces benzyl cation intermediates which react with alkynes to give functionalized products with very high regioselectivity.

Transition-Metal-Catalyzed Cleavage of C–N Single Bonds

“…The Lewis acid AuCl 3 is supposed to promote the formation of carbocationic species 53. afford various functional molecules, 54−57, via nucleophilic attack. These nucleophiles mainly include protic carbon nucleophiles, 102 protic sulfur nucleophiles, 102 alkynes, 103 βketo acids, 104 and arylallenes. 105 In the case of β-keto acids, the Fe-catalyzed reaction provides an effective decarboxylative alkylation of β-keto acids via sequential cleavage of C−N and C−C bonds.…”

“…105 In the case of β-keto acids, the Fe-catalyzed reaction provides an effective decarboxylative alkylation of β-keto acids via sequential cleavage of C−N and C−C bonds. 104 In the case of alkynes 103 and arylallenes, 105 the two reactions proceed via the Friedel−Crafts cyclization of carbocations to afford polysubstituted indenes 55 and 57, respectively.…”

“…The process for the formation of indene derivatives 55 was taken as an example to elucidate the mechanism (Scheme 19). 103 Benzyl cation 58 would first be generated from N-benzylic sulfonamide in the presence of FeCl 3 . This cation would then be attacked by the disubstituted internal alkyne to give vinyl cation 59, followed by a cyclization and an aromatization to form the indene derivatives 55.…”

Alkenylation of Arenes and Heteroarenes with Alkynes

“…Another example of the synthesis of indene derivatives 494 under the action of Fe(III) is the reaction of Nbenzylsulphonamides with internal alkynes (Scheme 276). 277,278 Under the action of FeCl 3 , the generation of a benzyl cation from a sulfonamide takes place. This cation further attacks the alkyne.…”