Acylketenes

Abstract

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Periselectivity in the aza-Diels–Alder Cycloaddition between α-Oxoketenes and N-(5-Pyrazolyl)imines: A Combined Experimental and Theoretical Study

“…α-Oxoketenes are short-lived chemical species with a long history, and with few exceptions, they cannot be isolated and must be generated in situ . They are routinely obtained either from the thermal decomposition of dioxinones with concomitant extrusion of acetone or from the thermal or photochemical Wolff rearrangement of 2-diazo-1,3-dicarbonyl compounds extruding nitrogen gas. , α-Oxoketenes are electrophilic species with widespread applications in organic synthesis, from the preparation of simple β-oxocarbonyl derivatives to the total synthesis of natural products , and complex heterocycles .…”

“…As to their annulation and cycloaddition reactions, they most commonly react with unsaturated substrates as 4π partners, i.e. 1-oxadienes, in inverse electron-demand formal Diels–Alder processes . However, in a few occasions, α-oxoketenes were found to react preferentially as 2π partners in normal electron-demand formal aza-Diels–Alder and 1,3-dipolar cycloadditions with 4π electron-rich substrates including 1-azadienes, 2-azadienes, and azomethine imines .…”

Periselectivity in the Aza-Diels–Alder Reaction of 1-Azadienes with α-Oxoketenes: A Combined Experimental and Theoretical Study

“…α-Oxoketenes [ 1 , 2 , 3 , 4 , 5 , 6 ] were first employed in organic synthesis in 1902 with the pioneering work of Ludwig Wolff on 2-diazo-1,3-dicarbonyl compounds [ 7 ]. Since, α-oxoketenes have revealed as versatile chemical intermediates for synthetic applications, ranging from the preparation of simple β-oxocarbonyl derivatives [ 8 ] to the total synthesis of complex natural products [ 4 , 5 ].…”

“…The most common and practical methods for the generation of α-oxoketenes are the thermal decomposition of dioxinones with concomitant extrusion of acetone [ 12 ], and the thermal or photochemical Wolff rearrangement of 2-diazo-1,3-dicarbonyl compounds extruding nitrogen gas [ 13 , 14 ]. α-Oxoketenes 1 are electrophilic species that most commonly react with imines through formal aza-Diels–Alder cycloadditions involving the α-oxoketenes as 4π reaction partners (1-oxadienes) and the imines as the 2π reaction partners to give 1,3-oxazin-4-ones of type 4 ( Scheme 1 ) [ 1 , 2 , 3 , 4 , 5 , 6 , 15 ]. However, when α,β-unsaturated imines 2 are employed, another formal aza-Diels–Alder process becomes possible, involving the α,β-unsaturated imines as 4π reaction partners (1-azadienes) and the α-oxoketenes as the 2π reaction partners to give hydropyridin-2-ones of type 3 [ 16 ].…”

Reactions of 2,2,6‐Trimethyl‐1,3‐dioxin‐4‐one with the Aryl Aldimines Prepared from Thiophene‐2‐carbaldehyde

“…The reactive intermediates known as acylketenes exhibit a rich chemistry and have been extensively utilized for many types of intermolecular and intramolecular bond‐forming reactions within the field of organic synthesis . Characteristic reactions of acylketenes include cycloadditions, carbon–carbon bond‐forming reactions, and nucleophilic capture with alcohols or amines to give β‐keto acid derivatives . An excellent source of acylketene is 2,2,6‐trimethyl‐1,3‐dioxin‐4‐one ( 1 ) by way of thermal extrusion of acetone (Scheme ).…”