Ketene-forming

The structure of the unusual betaine (50) has been determined (70JHC895). The bond lengths and angles suggest that a significant contribution to the structure is made by a resonance form (SOb) in which the N(l)—C(5) bond does not exist ( ketene form). 

An interesting suggestion was made by Levine in 1969. He supposed that the ketene formed photolytically from 1,2-naphthoquinone diazide could react with unreacted 1,2-naphthoquinone diazide to form a spirolactone-type addition product. This suggestion was tested experimentally almost twenty years later by Huang and Gu (1988). They irradiated 1,2-naphthoquinone diazide in dioxane in the presence of pyrene as sensitizer with a high-pressure mercury vapor lamp (Scheme 10-103). They did indeed obtain the spirolactonespiro(naphtho[4,5 2/,l/]furano-2-one)-3 T -inde-... 

Benzaldehyde and ketene form alternating copolymers with both cationic and anionic catalysts255. In the case of dimethylketene, crystalline alternating copolymers of... 

CO species in the adducted triiron complexes, the propargylidene-ketene compoimd has e same structure as compound 5 (ii) desilylation by the substitution of the silyl termin species with the ion originating from H2O or the solvent gives the hydrogen-ketene form. 

Unfortunately, some of the ketene formed decomposes further to form unwanted ethylene and carbon monoxide via the reaction ... 

Laboratory studies of these reactions indicate that the ketene selectivity S (kmol ketene formed per kmol acetone converted)... 

The effects of reactant structures on the ketene-forming elimination reactions of aryl esters of substituted phenylacetic acids (9) and (10) with secondary amines in acetonitrile (Scheme 2) have been studied in anticipation that the transition state might have E cB- kc E2 character.3 The reactions are second order for R2NH-MeCN and... 

The formal [2+2]-cycloaddition of imines to ketenes forms P-lactams. 

Similarly, the acetal 146 can undergo a thermal Wolff rearrangement to afford the intermediate ketene. Intramolecular nucleophilic attack of the acetal oxygen onto the ketene forms the zwitterion 147. Subsequent C-0+ bond cleavage and cyclization then furnishes dimethyl l,3-dimethoxy-l//-isochromen-4-yl phosphonate in excellent yield (Scheme 47) <1998T6457>. 

A series of (1-lactams (64) have been synthesized through the use of an immobilized cinchona alkaloid catalyst. This is postulated to proceed via the cycloaddition of an imine, and a ketene formed in situ through deprotonation of an acid chloride (Scheme 4.81). Different system configurations were described in the paper however, a column filled with a 5 1 mixture of solid K2C03 and immobilized-quinine derivative 65 cooled to —45 °C was found to be the most practical. The solution of the acid chloride and imine was dripped through the column and then directed... 

IOB alone epoxidizes some electron-deficient alkenes, in a reaction where its oxygen attacks the substrate nucleophilically. An example of this type was with tetracyanoethylene which was converted into its epoxide (74%) similarly, ketenes formed unstable a-lactones which polymerized [7],... 

Imagine the carbonyl group of a ketene forming an acetal in the same way as an aldehyde. In fact, they cannot be... 

Forms unstable explosive products in reaction with acetaldehyde + desiccants (forms polyethyUdine peroxide) acetic acid (forms peracetic acid) acetic + 3-thietanol acetic anhydride acetone (forms explosive peroxides) alcohols (products are shock-and heat-sensitive) carboxylic acids (e.g., formic acid, acetic acid, tartaric acid), diethyl ether, ethyl acetate, formic acid -f- metaboric acid, ketene (forms diacetyl peroxide) mercur f(II) oxide + nitric acid (forms mercur f(II) peroxide) thiourea -f- nitric acid polyacetoxyacryUc acid lactone + poly(2-hydroxyacrylic acid) + sodium hydroxide. 

The main reaction is followed by a slow pressure increase , which is due to the thermal decomposition of the ketene formed. It was proved that ketene is an intermediate . 

The pressure increase approaches 100 % at 368 °C and 5-10 torr initial pressure, but is less at higher pressures (probably due to the secondary reactions of the ketene formed). Surface effects are not significant, although the secondary reactions of the products are, to some extent, heterogeneous. 

In the absence of a substrate, diimide disproportionates to nitrogen and hydrazine, which combines with the ketene formed to give acetylhydrazide. 

Photolysis of hydroxy Fischer carbene complexes (96) (Scheme 20) in the presence of alcohols under several atmospheres of carbon monoxide gives low to moderate yields of a-hydoxy esters (97). It is proposed that the reactions proceed via ketenes formed from the liberated or complexed carbenes and CO. In some cases, acetals formed via thermal decomposition of the carbenes are the major products. Photolysis of iron porphyrin carbene complexes results in cleavage of the iron-carbon double bond, producing a four coordinate iron(II) porphyrin and the free carbene. The carbenes can be trapped in high yield with a variety of alkenes. 

Ketene formed after exposure can react with novo-lac macromolecules, especially when water molecules are completely absent. The result of such interactions is crosslinking of novolac macromolecules. 

The most studied of the mesoionic compounds are the mtinchnones (90), which are 3-substituted-5(4i/)-oxazolones with at most one substituent on the 4 position. They react in such a 1,3-dipolar form or in a ring-opened ketene form. Reactions of 3-unsubstituted-5(4/f)-oxazolones may also proceed through their mesoionic (91) or ketene (92) tautomers (Scheme 29). 

Apart from the well-known Arndt-Eistert homologization of carboxylic acids and the many and varied intermolecular reactions of the ketenes formed... 

Ziegler and coworkers have reported several DFT studies on organometallic systems. Representative examples of this work include the study of (i) C-H bond activation by [(cp)M(L)] (M = Rh, Ir L = CO, PH3) and M(CO)4 (M = Ru, Os) [106], (ii) ketene forming reactions involving bromine abstraction from 2-bromoacetyl chloride by [Mn(CO)s]- [107], (iii) intermediates and reaction steps in the HCo(CO)4 catalysed hydroformylation reaction [108] as shown in Fig. 6, (iv) the role of the carbene L2Mo(X)CH2 and the molybdacyclobutane... 

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