Cyclohexanones reactions with diazomethane

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. 

Nelson and Scliut investigated the reaction of 5a-cholestanone (lb) with diazomethane in a search for a direct, one-step preparation of A-homo ketones. Using a large excess of diazomethane generated in situ from A-methyl-nitrosourea with potassium hydroxide in ether-methanol at 0°, 5a-cholestanone (lb) is converted into the 7-membered ring homolog (3b) as the predominant product. Both theoretically possible A-homo ketones can be expected with an unsymmetrically-substituted cyclohexanone such as 5a-cholestanone (lb). 

Treatment of a cyclic ketone with diazomethane is a method for accomplishing a ring-expansion reaction. For example, treatment of cyclohexanone with diazomethane yields cycloheptanone. Propose a mechanism. 

Reaction of cyclic ketones with diazomethane leads to ring enlargement. Thus cyclohexanone (I) (1 mol) and diazomethane (1 mol) give c/oheptanone (II) in about 60 per cent, yield together with a little epoxide (III) as by product and some cyclooctanone (IV) resulting from further reaction of cycloheptanone with dlazomethane. ... 

Ring expansion. In early work3 the ring expansion of cyclohexanone to 2-methylcycloheptanone by reaction with ethereal diazoethane was found to proceed slowly and in poor yield. The results were confirmed by Marshall and Partridge.4 These chemists noted, however, that Mosettig5 had observed that methanol accelerates the reaction of cyclohexanone with diazomethane. They then carried out the ring expansion of cyclohexanone (1) with diazoethane in 20% ethanol in diethyl ether as solvent. The reaction was complete within 2 hours and gave a 9 1 mixture of 2-methylcycloheptanone (2) and the oxide (3) in over 90% yield. They also carried out the reaction on a number of 4-substituted cyclohexanones. 

The intermediacy of such oxaspiropentanes has been proposed in the addition of diazomethane to ketonesi0) and in the reaction of dimethyloxosulfonium methylide with a-haloketones55). In contrast to phosphorous ylides, sulfur ylides usually condense with carbonyl compounds to yield epoxides, thus reaction of the N,N-dimethylaminophenyloxosulfonium cyclopropylide 99 with cyclohexanone produced the dispiroepoxide 100 which rearranged to the spiro [3.5] nonan-l-one 101 upon isolation by gas chromatography, Eq. (29) S6). 

The intermediacy of oxaspiropentanes was first proposed in some reactions i.e. the addition of diazomethane to cyclohexanone the reaction of dimethyloxosulphonium methylide with a-haloketones and the reaction of iV,iV-dimethylaminophenyloxo-sulphonium cyclopropylide with ketones . The parent oxaspiropentane (115) has been obtained from the p-nitroperbenzoic acid oxidation of a methylene chloride solution of methylenecyclopropane (69) at - 10°C (equation 82). ... 

There are few examples of this variation in the literature. The variation relies on the alkylation of thiolactams (in replacement of cyclohexanones) by the Michael addition of diazomethyl vinyl ketone (in replacement of methyl vinyl ketones) followed by ring closure using rhodium(II) acetate mediated diazomethane insertion. The diazomethyl entity can also be added after the Michael addition step. The reaction affords six-membered rings with... 

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