Silver oxide Wolff rearrangement

The diazo ketone 3, when treated with silver oxide as catalyst, decomposes into ketocarbene 5 and dinitrogen Na. This decomposition reaction can also be achieved by heating or by irradiation with uv-light. The ketocarbene undergoes a Wolff rearrangement to give a ketene 6 ... 

The main synthetic application of the Wolff rearrangement is for the one-carbon homologation of carboxylic acids.242 In this procedure, a diazomethyl ketone is synthesized from an acyl chloride. The rearrangement is then carried out in a nucleophilic solvent that traps the ketene to form a carboxylic acid (in water) or an ester (in alcohols). Silver oxide is often used as a catalyst, since it seems to promote the rearrangement over carbene formation.243... 

Treatment with silver oxide in water causes these a-diazoketones to undergo the Wolff rearrangement, yielding 2-deoxyaldonic acids (Scheme 6).95... 

This ester is one carbon atom short of the full side chain of grandisol, so an Arndt-Eistert reaction was used to lengthen the chain by one atom. First, the ester was converted into the diazoketone with diazomethane and, then, the Wolff rearrangement was initiated by formation of the carbene with a Amdt-Eistert chain extension of ester silver compound at the Ag(II) oxidation state. 

The use of transition metal species can lower appreciably the decomposition temperature of ot-diazo-carbonyl compounds they can also alter the reactivity of the carbene intermediate (resulting from the initial nitrogen elimination see Section 3.9.2.1) by complex formation. Hence, the Wolff rearrangement may occur with difficulty or, usually, not at all. Thus, some copper species (excepting, for example, Cul), or Rh and Pd catalysts are inappropriate. Freshly prepared silver(I) oxide has been used most frequently, but silver salts (especially silver benzoate) are sometimes preferred.Silver-based catalysts are usually employed in combination with an alkaline reagent e.g. sodium carbonate or a tertiary amine). Even under silver catalysis competing reactions may be observed, and sometimes the products of Wolff rearrangement may not be obtained (see Section 3.9.2.3). 

Wolff rearrangement. Finding that the Wolff rearrangement of diazoketones with silver oxide and methanol gave erratic, highly variable results, Newman and Beal developed a procedure for carrying out the reaction in homogeneous solution under mild conditions. A solution of diazoacetophenone in methanol was treated at room temperature with a few drops of a filtered solution of 0.004 mole of silver... 

The Wolff rearrangement of l-deoxy-l-diazo-3,4,5,6-di-0-cyclohexylidene-D-arabinohexulose 93 in the presence of ammonia and silver(I) oxide afforded 2-deoxyhexonamide 95, whereas the reaction with benzylamine and para-substituted anilines resulted in the preferential formation of A -substituted 2,3-dideoxy-2-hexenonamides 96. ... 

The acetylated diazomethyl ketoses undergo the Wolff rearrangement (166) when treated in water with silver oxide to give a mixture of 2-deoxy-aldonic lactones (167). 

Heating of the diazoketone (36) in methanol or ethanol in the presence of silver oxide gave the 2,3-dideoxyalkenes (37, 38) instead of the expected products of Wolff rearrangement (39, 40) (Scheme 17). ... 

There are several experimental methods for effecting the Wolff rearrangement. The classical technique for preparation of acids or esters involves thermal decomposition in the presence of silver oxide in an aqueous solution (for acids) or an alcohol (for esters). At least for unsaturated diazoketones, the silver oxide seems to direct the reaction toward the rearrangement pathway in preference to carbenoid addition.Photolysis in nonnucleophilic solvents generates the ketene, which can undergo subsequent reactions in situ or, if sufficiently stable, be isolated. 

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