New method for C–H arylation/alkylation at α-position of cyclic aliphatic ethers by iron-oxide mediated reaction

Abstract

We report a new and efficient iron oxide catalyzed cross-coupling reaction between organometallic species such as alkyl/arylmagnesium halides or organolithium species and α-hydrogen bearing cyclic unbranched and branched aliphatic ethers via activation of C(sp(3))-H. In the presence of 1 mol% of iron oxide, five and six membered unbranched cyclic ethers such as tetrahydrofuran and tetrahydropyran gave good to excellent yields of cross-coupled products. Whereas, in case of branched ether such as 2-methyltetrahydrofuran, it was observed that the arylation occurred at both the sides and gave moderate yields of a mixture of regioisomers. Among the organometallic species used, alkyl organometallic reagents gave less yields as compared to aryl organometallics.

Preparation of arylmagnesium/lithium from aryl bromides and their coupling and substitution reactions in tetrahydrofuran

“…For this reason, in situ prepared PhMgBr was treated with 2‐methyltetrahydrofuran. As expected, spectral analysis of the crude material clearly showed an isomeric mixture of arylation product of 2‐methylfuran was formed as reported in the literature …”

“…Vishwakarma and co‐workers also reported an iron oxide‐catalysed cross‐coupling reaction between organometallic species and α‐hydrogen‐bearing cyclic aliphatic ethers . In this context, Ghosh and co‐workers explored the cross‐coupling of tetrahydrofuran (THF) with Grignard reagents in the presence of a nickel catalyst .…”

Iron‐catalyzed C−H Activation

“…In 2011, Singh's group reported a novel iron oxide‐catalyzed cross‐coupling reaction between organometallic halides and hydrogen‐bearing cyclic ethers such as tetrahydrofuran via direct activation of a C(sp 3 )–H center . In 2012, Weiping et al .…”

Direct Functionalization of Tetrahydrofuran and 1,4‐Dioxane: Nickel‐Catalyzed Oxidative C(sp3)H Arylation

“…Moreover, the oxidative arylation of C(sp 3 )H bonds adjacent to nitrogen atoms has also been demonstrated in recent years 7. However, to the best of our knowledge, only isolated examples of the oxidative arylation of C(sp 3 )H bonds adjacent to oxygen atoms (ether derivatives) with aryl nucleophiles have been reported to date 2b,c…”