Abstract
Continuous flow systems offer unique benefits in the generation and manipulation of sensitive reactive intermediates such as ketenes. To this end, the last decade has witnessed the development of continuous flow methods for the generation of ketenes by means of chemical, thermal, and photochemical activation modes. This perspective covers these advances and the downstream reactivity of ketenes in continuous flow technology.
Highlights
Ketenes in organic synthesisMany transformations in organic synthesis deliver the desired product through reactive intermediate species
Formation and utility of reactive ketene intermediates under continuous flow conditions Harry R
The use of prepacked columns containing powdered zinc metal was explored by Ley and Hafner to bring about a continuous flow dehalogenation process for the in situ generation of reactive ketenes (Scheme 3) [19,20]
Summary
Many transformations in organic synthesis deliver the desired product through reactive intermediate species These are usually short lived, high energy, highly reactive molecules, which in turn renders their isolation and formal characterisation challenging. Over the following two years e after the initial discovery e Staudinger reported a wide range of reactions of ketenes including: [2 þ 2] self-dimerization; cycloadditions to form blactams (Staudinger synthesis); and cycloadditions to form b-lactones [5,6] (Scheme 1A). Staudinger pursued this ketene chemistry for the 20 years before later focusing on polymer chemistry, for which he obtained the Nobel Prize in 1953 [7]. The following sections highlight recent endeavours to generate these reactive ketene intermediates under a continuous flow regime, employing chemical, thermal, microwave-assisted, and photochemical conditions for their generation
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