Ring-expanded ketone

Reaction of the morpholine or piperidine enamine of cyclopentanone, however, gives an unstable adduct which rearranges under the reaction conditions and an aqueous work-up to give the ring expanded ketone 2-chloro-2-cyclohexen-l-one (203) (138,139). 

In general, it is better to make such compounds by hydroxylation of the alkene, There is no problem with the alkene rearrangement here, the ring expanded ketone (20) being formed in good yield. This product can also be made by another rearrangement route (see p 120). Synthesis... 

The reaction of ketones with diazomethane sometimes leads to a ring-expanded ketone in synthetically useful yields.79 The reaction occurs by addition of the diazomethane, followed by elimination of nitrogen and migration. 

Ring expansion of cyclohexanone to cycloeheptanone may be effected by reaction with diazomethane (Expt 7.17). The ring-expanded ketone is obtained in about 60 per cent yield and is accompanied by some epoxide and some cyclo-octanone which results from further ring expansion of the cycloheptanone. Mechanistically the reaction may be represented in the following manner. 

The tetrahedral intermediate B of Figure 11.20 is not enriched to any significant concentration because the ring expansion reaction, which it undergoes, is at least as fast as its formation. Once the first ring-expanded ketone is formed, there obviously still is plenty of unreacted substrate ketone A present. The question is now which ketone re-... 

Many other 1,2-carbonyl transpositions with skeletal rearrangement are known. In general, aldehydes react more rapidly than ketones the rearrangement of a ketone to form an aldehyde appears to be unknown, but ketones can be converted to other ketones. A few examples from the early work of Venus-Danilova ° are illustrated. Thus cyclobutane- and cyclopentane-carbaldehyde both gave the simple ring-expanded ketones as shown in equations (5) and (6), upon treatment with concentrated sulfuric acid. 

The symmetrical diols derived from cyclopentanone and cyclohexanone can similarly be converted to ring-expanded ketones in good yield. The diols from reductive coupling of cycloheptanone and cy-clooctanone give mainly the corresponding dienes in aqueous acid, especially when heated, but Chris-tol found that pinacol rearrangement is strongly favored even for these materials when cold concentrated sulfuric acid is used as the solvent. 

The anion of 1,1-dithiophenoxymethane adds to cyclic ketones and the adduct then rearranges to a ring-expanded ketone on metal salt catalysis (equation 28). The least-substituted group migrates in this case, as in the trithioalkyl derivative (24 equation 29), which was utilized in a synthesis of coriolin. ... 

Photochemical decomposition of malonic acid by irradiation in solution has been reported. Some of the radical species produced by this treatment are identical to those formed by the Ce decomposition of malonic acid in the Belousov-Zhabotinsky reaction. The (2 + 2)-cycloadducts (172) can be readily prepared by irradiation of mixtures of the corresponding enone and alkene, and these adducts can conveniently be converted into the hydroperoxide (173) by irradiation at 366 nm in the presence of air and acridine in toluene.The decarboxylation occurs by a free radical pathway and treatment of the hydroperoxide with dimethyl sulfide brings about formation of the ring-expanded ketones or lactones (174),... 

The bromochlorocarbene adduct 12 to the silyl enol ether of a cycloheptanone derivative, forms, without isolation, a ring-expanded ketone 13 as the main product, when treated with tetrabutylammonium fluoride. 

In the analogous reactions with bicyclo[3.1.0]hexan-2-ols 33 a much greater proportion of the ring-expanded ketone 35 was obtained. This is in keeping with the known propensity of the intermediate radical to undergo both modes of ) -scission. 

Deprotonation of (7.111) gives the ring expanded ketone (7.102). Such are the forces driving selectivity of this reaction that only 5% of the starting material followed other reaction paths. 

A useful one-carbon ring-expansion reaction which has been developed involves treatment of l-(dibromomethyl)-cycloalkan-l-ols with n-butyl-lithium in hexane to give the ring-expanded ketones, usually in excellent yield e.g. l-(dibromomethyl)-cyclododecan-l-ol, which was obtained by treating cyclododecanone with dibromo-methyl-lithium, gave cyclotridecanone in 89% isolated yield. ... 

Tiffeneau and co-workers reported their discovery of the reaction in 1937 for the ring expansion of hydroxy-cyclohexylmethyl amine 10 to form cycloheptanone 11. This reaction also has been applied to numerous cases in which a ring expanded ketone was formed. 

Because treatment of a primary aliphatic amine with HNO2 gives a mixture of products, it is generally not a useful reaction. An exception is the Tiffeneau-Demjanov reaction, in which a cychc 8-aminoalcohol is treated with nitrous acid to give a ring-expanded ketone, with evolution of nitrogen. 

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