6-Oxocyclohexa-2,4-dienylideneketene:  A Highly Reactive α-Oxoketene

Abstract

The title ketene 2 has been generated by laser flash photolysis and observed in solution for the first time, using time-resolved infrared spectroscopy. The kinetics of the reactivity of 2 with H2O, MeOH, and Et2NH with relative reactivities of 1.0, 2.0, and 73 have been measured. These are the first direct measurements of the reactivities of a ketene with these different nucleophiles under the same conditions. Ab initio molecular orbital calculations indicate the hydration occurs by in-plane attack of the H2O molecule on the ketenyl carbonyl through a pseudopericyclic transition state with assistance by coordination to the keto-carbonyl.

Synthesis of Functionalized Salicylate Esters and Amides by Photochemical Acylation

“…The efficient photochemical acylation of anti ‐β‐isopropanoyloxy alcohol ( 14 g ) represents an alternative approach to a key fragment 15 g in our synthesis of salicylihalamides 18. On the basis of these results and in line with the proposed pseudopericyclic transition state,10a this reaction appears to be less sensitive to steric bulk in the alcohol than classical acylation reactions 19. For more quantitative information, we performed a competition experiment between 5‐hexyn‐1‐ol and 1‐methyl‐cyclohexanol ( 14 d ) for photoacylation with benzodioxinone 5 [Eq.…”

“…(1)] 10. In the same report, Tidwell and co‐workers also detailed quantitative reactivity studies and proposed a pseudopericyclic transition state for the capture of C (R=H) with water, methanol, and diethylamine 10a. Despite this theoretical and mechanistic interest, and contrary to the situation with α‐oxoketenes,9b the synthetic exploitation of quinoketenes for the formation of salicylate esters and amides remains largely unexplored 11.…”

The emerging utility of ketenes in polymer chemistry

“…(A)]. Inspired by Tidwell et al, Soltani and Brabander developed methodology using this class of compounds for the construction of an array of small molecule salicylate esters . The mild photo‐activation and highly efficient coupling chemistry of these molecules make them attractive in applications that require on‐demand reactivity.…”

“…The chemistry of benzodioxinones, as shown in Figure , involves a photolysis of substrate 12 into quinoketene 13 and benzophenone. The quinoketene has been observed spectroscopically and is well known to be trapped by alcohols or amines to form the corresponding salicylic ester ( 14 ) or amide.…”

NO-NSAIDs. Part 3: Nitric Oxide-Releasing Prodrugs of Non-steroidal Anti-inflammatory Drugs

“…We believe that these imide prodrugs 25 and 27, because of their distinct differences in metabolic stability (t 1/2 =9 min versus 150 min) and degradation pattern in rat and/or human plasma, qualify themselves as ideal candidates for such mechanistic studies. 33,34) The stability of such lactone form (i.e., TI2B) was reported to be nearly equal to o-oxoketene (TI2A) and it could be attributed to aromatic stabilization, which might be partially offset by its ring strain. The photochemical inter-conversion of TI2A and TI2B has also been reported earlier.…”