in acetic acid, and the resulting product reacts with methoxide in methanol to give the secondary α-diazo ketone. Diazo-transfer reactions Diazo-transfer reactions are commonly used methods, in which an organic azide, usually tosylazide, and an activated methylene (i.e. a methylene with two withdrawing groups) react in the presence of a base to give an α-diazo-1,3-diketone. The base deprotonates the methylene, yielding an enolate, which reacts with tosylazide and subsequently decomposes in the presence of a weak acid, to give the α-diazo-1,3-diketone. The necessary requirement of two electron withdrawing groups makes this reaction one of limited scope. The scope can be broadened to substrates containing one electron withdrawing group by formylating a ketone via a Claisen condensation, followed by diazo-transfer and deformylative group transfer. One of the greatest advantages of this method is its compatibility with unsaturated ketones. However, to achieve kinetic regioselectivity in enolate formation and greater compatibility with unsaturated carbonyls, one can induce enolate formation with lithium hexamethyldisilazide and subsequently trifluoroacylate rather than formylate. Methods for inducing rearrangement Wolff rearrangements can be induced under thermolytic, photolytic, and transition-metal-catalyzed conditions. Thermal conditions to induce rearrangement require heating to relatively high temperatures, of 180 ˚C, and thus have limited use. Many Wolff rearrangement products are ring-strained and are susceptible to ring-open under high temperatures. In addition, SN2 substitution of the diazo group at the α-carbon can take place at lower temperatures than rearrangement, which results in byproducts. The greatest use of thermal Wolff rearrangements is the formation of carboxylic acid analogs, by interception of the ketene with high boiling solvents, such as aniline and phenol. Transition metals greatly lower the temperature of Wolff rearrangements, by stabilization of a metal-carbene intermediate. However, these carbenes can be so stable, as to not undergo rearrangement. Carbenes of rhodium, copper, and palladium are too stable and give non-Wolff products (primarily carbene insertion products). The most commonly used metal catalyst is silver(I) oxide, although silver benzoate is also common. These reactions are generally run in the presence of a weak base, such as sodium carbonate or tertiary amines. Whereas thermal and metal mediated Wolff rearrangements date back to 1902, photolytic methods are somewhat newer, with the first example of a photolytic Wolff rearrangement reported in 1951. α-diazo ketones have two absorption bands, an allowed π→π* transition at 240–270 nm, and a formally forbidden π→σ* transition at 270–310 nm. Medium or low-pressure mercury arc lamps can excite