Diazoalkanes reaction with ketene

The most common reaction involving this type of cycloaddition is the reaction of ketenes with diazoalkanes (Houben-Weyl, Vol. 4/4, pp 406-408) which proceed via cyclopropanone intermediates. This type of reaction finds limited use due to nonregioselective formation of substituted cyclobutanones as mixtures. 

A significant advance in the study of cyclopropanones resulted from studies by the Turro and the de Boer groups on the formation of cyclopropanones in solution by the reaction of ketenes with diazoalkanes. These investigators found that it is possible to store the parent ketone only for short periods at low temperature because of its unusual reactivity and propensity for polymerization. Subsequent work has shown that cyclopropanone seems to show chemical behavior similar to that of ketene. Thus, it is attacked by nucleophilic species such as water, alcohol and amines and reacts rapidly with itself to form... 

Cyclobutanones may be prepared without isolating the intermediate cyclopropanone by adding the ketene to excess diazoalkane (-78°C, 30 min) . The intermediacy of cyclopropanones in this process has been shown by C-labeling studies and by comparison of the product distributions in the diazoalkane-ketene with the corresponding diazoalkane-cyclopropanone reactions. When the cyclopropanone precursor is un-symmetrically substituted, the reaction with diazomethane leads to a mixture of cyclobutanones . 

The reaction of diazoalkanes with ketenes at low temperature is a classical way of preparing cyclopropanones in solution. ... 

Irradiation of diazoketones (reactions 8.7 and 8.8) [17-19], diazoesters (reaction 8.9) [20], and various other diazoalkanes (reactions 8.10 and 8.11) [21,22] as well as diazirines (reactions 8.12 and 8.13) [23,24] under matrix isolation conditions also led to the detection of the corresponding carbene intermediate, which could be trapped with carbon monoxide in the form of ketenes. For example. 

Despite the fragmentary results known to date, the dediazotation of diazoalkanes coupled with the carbene-carbon monoxide trapping reaction seems to be a promising synthetic path for the preparation of various carboxylic acid derivatives through the ketene intermediate product. Especially the highly effective and selective cobalt-catalyzed examples of the reactions are worth to explore in more detail. 

The transition metal-catalyzed cyclopropanation of alkenes is one of the most efficient methods for the preparation of cyclopropanes. In 1959 Dull and Abend reported [617] their finding that treatment of ketene diethylacetal with diazomethane in the presence of catalytic amounts of copper(I) bromide leads to the formation of cyclopropanone diethylacetal. The same year Wittig described the cyclopropanation of cyclohexene with diazomethane and zinc(II) iodide [494]. Since then many variations and improvements of this reaction have been reported. Today a large number of transition metal complexes are known which react with diazoalkanes or other carbene precursors to yield intermediates capable of cyclopropanating olefins (Figure 3.32). However, from the commonly used catalysts of this type (rhodium(II) or palladium(II) carboxylates, copper salts) no carbene complexes have yet been identified spectroscopically. 

Ketenes rarely produce [3+ 2]-cycloaddition products with diazo compounds. The reaction possibilities are complex, and nitrogen-free products are often obtained (5). Formation of a cyclopropanone represents one possibihty. Along these lines, the synthesis of (Z)-2,3-bis(trialkylsilyl)cyclopropanones and (Z)-2-trialkylsilyl-3-(triethylgermyl)cyclopropanones from diazo(trialkylsilyl)methanes and appropriate silyl- or germylketenes has been reported (256,257). It was found that subsequent reaction of the cyclopropanone with the diazoalkane was not a problem, in contrast to the reaction of diazomethane with the same ketenes. The high cycloaddition reactivity of diazomethylenephosphoranes also extends to heterocumulenes. The compound R2P(C1)=C=N2 (R = N(/-Pr)2) reacts with CS2, PhNCO and PhNCS to give the corresponding 1,2,3-triazole derivative (60). 

Examples of tetratopic reactions are the C—N bond dissociation in azo compounds, discussed in Section 7.2.2, C—X bond dissociation in alkyl halides, and the O—O bond dissociation in peroxides. Examples of pentatopic reactions are the dissociation of the C—X bond in vinyl halides, of the C=C bond in ketenes, and of the C—N bond in diazoalkanes. An example of a hexatopic bond dissociation is the fragmentation of an alkyl azide to a ni-trene and N,. A verification of the topicity rules at a semiempirical level was reported (Evleth and Kassab, 1978), and a detailed description of the electronic structure aspects of bond dissociations characterized by various topicity numbers, with references to the original literature, has appeared recently (Michl and BonaCi<5-Koutecky, 1990). 

Diazoalkane carbonylation using palladium catalysis gives unobserved acylketenes, which are captured in situ with nucleophiles (Scheme 7.43). The reactions are suggested to involve palladium complexed ketenes and are carried out with various substrates and nucleophiles. 

Diazoalkanes are decomposed by nickel carbonyl yielding nitrogen and reaction products indicative of the presence of carbenes as intermediates (25). Although carbenes usually show little tendency to combine with carbon monoxide, formation of ketenes was detected by decomposing the diazoalkanes in the presence of excess nickel carbonyl. This carbonylation of carbenes undoubtedly occurs via nickel-carbene complexes (25)... 

According to theoretical calculations, there is a low-energy pathway for the direct interaction of diazomethane with carbon monoxide [4j. However, experimental results so far show only evidences for two-step pathways. These involve first the dediazotation of the diazoalkanes in thermal, photochemical, or transition metal mediated reactions [5] resulting in free carbenes (Equation 8.2) or transition metal coordinated carbenes (Equation 8.3), which under proper reaction conditions couple in the second step with carbon monoxide (Equation 8.4 or 8.5) to form ketene products. 

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