Ring Enlargement of Three-Membered Heterocycles by Treatment with In Situ Formed Tricyanomethane.

Klaus Banert,Marcus Korb,Madhu Chityala

doi:10.1002/chem.202000089

Klaus Banert, Marcus Korb + Show 1 more

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https://doi.org/10.1002/chem.202000089

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Abstract

Although the chemistry of elusive tricyanomethane (cyanoform) has been studied during a period of more than 150 years, this compound has very rarely been utilized in the synthesis or modification of heterocycles. Three‐membered heterocycles, such as epoxides, thiirane, aziridines, or 2H‐azirines, are now treated with tricyanomethane, which is generated in situ by heating azidomethylidene‐malonodinitrile in tetrahydrofuran at 45 °C or by adding sulfuric acid to potassium tricyanomethanide. This leads to ring expansion with formation of 2‐(dicyanomethylidene)oxazolidine derivatives or creation of the corresponding thiazolidine, imidazolidine, or imidazoline compounds and opens up a new access to these push–pull‐substituted olefinic products. The regio‐ and stereochemistry of the ring‐enlargement processes are discussed, and the proposed reaction mechanisms were confirmed by using 15N‐labeled substrates. It turns out that different mechanisms are operating; however, tricyanomethanide is always acting as a nitrogen‐centered nucleophile, which is quite unusual if compared to other reactions of this species.

Highlights

The history of tricyanomethane (5) dates back to 1864 when the first isolation of so-called cyanoform was reported.[1]
We expected that 5 resulting from 7 would O-protonate 9 a, and the nucleophilic attack of the central carbon atom of the tricyanomethanide counterion would lead to the ring-opened product 10 a, which can possibly react to 12 a by nucleophilic addition of the hydroxy group at a cyano unit
We have demonstrated that tricyanomethane (5), in situ generated by thermal decay of vinyl azide 7 or by acidification of tricyanomethanide salt 1 b, can successfully be used to perform ring-expansion reactions with three-membered heterocycles

Summary

Introduction

The history of tricyanomethane (5) dates back to 1864 when the first isolation of so-called cyanoform was reported.[1]. We expected that 5 resulting from 7 would O-protonate 9 a, and the nucleophilic attack of the central carbon atom of the tricyanomethanide counterion would lead to the ring-opened product 10 a, which can possibly react to 12 a by nucleophilic addition of the hydroxy group at a cyano unit.

Results

Conclusion