Isotopic labelling studies for a gold-catalysed skeletal rearrangement of alkynyl aziridines

Abstract

SummaryIsotopic labelling studies were performed to probe a proposed 1,2-aryl shift in the gold-catalysed cycloisomerisation of alkynyl aziridines into 2,4-disubstituted pyrroles. Two isotopomers of the expected skeletal rearrangement product were identified using 13C-labelling and led to a revised mechanism featuring two distinct skeletal rearrangements. The mechanistic proposal has been rationalised against the reaction of a range of 13C- and deuterium-labelled substrates.

1,2-Boryl Migration Empowers Regiodivergent Synthesis of Borylated Furans

“…Diynyl epoxide 4j afforded alkynylated furan 5j exclusively in 67% yield. Remarkably, employment of trisubstituted oxirane 4k in this transformation led to the exclusive formation of furan 5k in 83% yield, thus, indicating overwhelming preference of boryl group versus aryl group 1 , 2a − 2c , 3 migration. Analogously, dialkyl-containing furan 5e was selectively obtained under these conditions.…”

“… 2 Recently, Davies’ group efficiently employed alkynyl aziridine 1 in a gold-catalyzed cycloisomerization toward either 2,4- or 2,5-substituted pyrroles 2 and 3 (Scheme 1 , eq 1). 3 The regioselectivity of this reaction is governed by the basicity of counterion, where the less basic triflate favors migration of an aryl group to afford 2 , while a more basic tosylate leads to pyrrole 3 , the product of a formal 1,2-hydrogen shift. Herein we report a regiodivergent copper- and gold-catalyzed cycloisomerization reactions of boron-containing alkynyl epoxide 4 toward C3- and C2-borylated furans 5 and 6 (Scheme 1 , eq 2).…”

Ring Expansions of Activated Aziridines and Azetidines

“…They studied the counter ion effect on the goldcatalyzed transformations for determining the reaction pathways to produce isomeric pyrrole derivatives [100][101][102]. Gold catalysis is a powerful tool to activate alkynes through π-donation.…”

[1, 2]‐Migration Reactions Catalyzed by Gold Complexes and their Applications in Total Synthesis

“…Davies and co‐workers demonstrated that the gold(I)‐catalyzed rearrangement of alkynyl aziridines gave pyrroles (Scheme ) . The reaction proceeds under mild conditions at room temperature.…”