Vinylketenes
Reactive class of chemicals
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Vinylketenes are a class of chemical compounds where a vinyl group is conjugated to a ketene. Vinylketenes are key intermediates in the Danheiser benzannulation and Wulff-Dötz reaction, two routes to synthesis of phenols.
Preparation
Vinylketenes are typically prepared in situ. Dehydrohalogenation of butenoyl chloride produces 1,3-butadienal, with substituted acyl chlorides likewise producing substituted vinylketenes; however, this method can be undesirable as the byproduct contains organic ammonium chloride derivatives that catalyse ketene polymerisation.[1]
Vinylketenes may be prepared by electrocyclic ring opening of cyclobutenones. In the Danheiser benzannulation, vinylketene is produced via Wolff rearrangement of a vinyl-conjugated diazoketone.[2][3]
Reactions
Vinylketenes are highly reactive versus polymerisation, but can be stabilised as organometallic coordination complexes. Typically, the vinylketene is a tetrahaptic ligand similar to a diene. Vinylketenes can also exhibit dihapticity when prepared from η2(C,O) ketene complexes via an intermediate vinylogous acylium complex.[4]