Recent advances in ketene chemistry

Abstract

Recent advances in ketene chemistry are reviewed, including synthetic, mechanistic, and computational studies. Topics include ketene structure determination by experimental and theoretical methods, computational studies of bonding in ketenes, spectroscopic properties of ketenes, preparation and formation of ketenes including photochemical and thermal methods, the discovery and observation of ketenes in space, and ketene reactions. The last category includes decarbonylation, cycloadditions with carbon-carbon, carbon-nitrogen, and carbon-oxygen multiple bonds, addition of oxygen, nitrogen, and carbon nucleophiles, and electrophilic additions.

Catalyst-free formal [4+1]/[4+2] cyclization cascade sequence of isocyanides with two molecules of acylketene formed in situ from thermal-induced Wolff rearrangement of 2-diazo-1,3-diketones

“…Based on the aforementioned results and previous reports [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][57][58][59], a possible reaction mechanism was proposed in Scheme 4. Initially, the thermal-induced decomposition of 2diazo-1,3-diketone 2 leads to the formation of acylketene intermediate Int-I by Wolff rearrangement, followed by the intermolecular nucleophilic attack of isocyanides 1 yielding the highly reactive nitrilium ion intermediate Int-II.…”

“…They can react as versatile C4 synthons with different nucleophiles and dienophiles. In most cases, these reactions give rise to products of formal [4+1] [38][39][40][41][42][43] or [4+2] [44][45][46][47] cycloaddition. In particular, reactions of acylketenes with the C@N double bond of imines leads to derivatives of 1,3-oxazines [48][49][50].…”

Direct/Reversible Amidation of Troponyl Alkylglycinates via Cationic Troponyl Lactones and Mechanistic Insights

“…6b The reaction mechanism was proposed based on the control experiments and literature reports. 4d,9 These control experiments revealed the key role of α-CH 2 and the troponyl moiety in the cleavage of the amide bond. However, understanding the role of glycinate α-CH 2 in the formation of CTLs with experimental evidences is very important.…”

Mechanism of Silver-Catalyzed [2+2] Cycloaddition between Siloxy-Alkynes and Carbonyl Compound: A Silylium Ion Migration Approach

“…Ketene has attracted many attentions all the time for its special structure which can act as key active intermediate in the cycloaddition, nucleophilic additions or electrophilic additions. [29] The current existing report mainly concentrated on carbon substituted ketene species. [25,30] According to our calculations, silver-ketene is only 1.1 kcal/mol less stable than A-int1 (see Figure 2, A-int5).…”