Rearrangements promoted by adjacent heteroatoms

Ring Expansion of Cyclic Ketones with Diazo Compounds 

More recently, it has been found that trimethylsilyl cyanide reacts with ketones to give trimethylsilyl ethers of cyanohydrins. These compounds can be directly reduced to the aminomethylcarbinol by lithium aluminum hydride. Another method for 

Diazotization of aminomethylcycloalkanes can also lead to ring expansion, but due to the absence of participation by a hydroxyl group in the rearrangement, this is a much less specific reaction and mixtures of alkenes and alcohols, both rearranged and unrearranged, are usually obtained. The reaction is seldom synthetically attractive. 

The reactions of ketones with diazoalkanes sometimes lead to a ring-expanded 

In protic solvents, at least, the reaction proceeds via essentially the same intermediate that is involved in the Tiffeneau-Demjanov reaction. Since the product is also a ketone, subsequent addition of diazomethane can lead to higher homologs. The best yields are obtained when the starting ketone is more reactive than the product. For this reason, strained ketones often work well in this reaction. Higher diazoalkanes can also be employed. The reaction has been found to be accelerated by alcoholic solvents. This effect probably involves the hydroxyl group acting as a proton donor and thus facilitating the addition step. 

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