Gold(I)-catalyzed hydroarylation of allenes with indoles

Abstract

Reaction of a monosubstituted, 1,3-disubstituted, or tetrasubstituted allene with various indoles catalyzed by a 1:1 mixture of a gold(I) N-heterocyclic carbene complex and AgOTf at room temperature leads to hydroarylation with formation of 3-allyl-indoles in modest to good yield.

Gold‐Catalyzed Functionalization Reactions of Indole

“…[40] According to the authors the formation of alkyl-ated indoles 23 could be ascribed to initial activation of the allene by cationic gold(I) to generate a π-allene complex of type XII, followed by nucleophilic attack by indole, yielding an intermediate of type XIII. The first example was reported in 2009 by Widenhöfer, who studied the reactions between non-activated allenes 22 and indoles 1 in the presence of simple AuCl/AgOTf as catalyst, affording (E)-allylic indoles 23 (Scheme 10).…”

Gold(I)‐Catalysed Hydroarylation of 1,3‐Disubstituted Allenes with Efficient Axial‐to‐Point Chirality Transfer

“…The 1:3r egioselectivity under these conditions, albeit modest, was also as urprise, because hydroarylation with allene 1n was previously reported to be non-regioselective (1:1.2) under racemic conditions. [16] Finally,a nd as predicted, the stericallyd ifferentiated dialkyl-substituteda llene 1o providedv ery poor regioselectivity (3/3', 1.4:1). This result supports our initial theory that it is electronic rather than steric factors that influence the regioselectivity of the gold-catalysed hydroarylation reaction (Scheme 2b).…”

“…Although these observations proved that substituents capable of stabilising the cationic intermediate I are detrimental to efficient chirality transfer, the effect was not quite as drastic as originally predicted. The 1:3 regioselectivity under these conditions, albeit modest, was also a surprise, because hydroarylation with allene 1 n was previously reported to be non‐regioselective (1:1.2) under racemic conditions . Finally, and as predicted, the sterically differentiated dialkyl‐substituted allene 1 o provided very poor regioselectivity ( 3 / 3 ′, 1.4:1).…”

“…Finally,e lectron-rich aryl substrates were tested as nucleophiles in our system (entries [15][16]. To our delight, methoxysubstituted species 2o reacted smoothly to give the desired product 3co in excellent yield (98 %) and regioselectivity (> 20:1), and good chirality transfer (90:10 e.r., entry 15).…”

Gold(I)‐Catalyzed Enantioselective Desymmetrization of 1,3‐Diols through Intramolecular Hydroalkoxylation of Allenes

“…[10] Similarly, no hydroarylation of allene was observed during the preparation of 2s by this method (entry 19). [11] These results feathered the counterion controlled reactivity in homogeneous gold catalysis. [12] Finally, the reaction was easily extended to substrates incorporating a protected amine functionality at the C 2 position.…”