By Wolff rearrangement

Photoelimination of nitrogen from diazoketones is complicated by Wolff rearrangement of the intermediate carbene, as shown below for diazoaceto-phenone<35) ... 

Table 1. Cyclobutanecarboxylic Acid Derivatives by Wolff Rearrangement of a-Diazocyclopentanones...

The vinyl ketene 184, formed by Wolff rearrangement of the vinylcarbene 183, in contrast adds across the N=N bond of excess 182 to give the adduct 185 (Scheme 64). 2... 

Appropriately substituted diazo ketones have been converted into oxetanes in two instances by Wolff rearrangement processes. The structure of compound (52) was established by X-ray crystallography (69MI51300, 81CSC345). Reaction of 4,4-dibromo-2,2,5,5-tetramethyltetrahydro-3-furanone with aqueous base is a good method of preparation for 3-hydroxy-2,2,4,4-tetramethyloxetane-3-carboxylic acid (equation 90) (66JA1242). 

Desulfonylation of a-sulfonylacetates. Desulfonylation of these substrates is not satisfactory by the usual methods (Zn-HOAc, Raney Ni-C,H5OH, sodium amalgam), but can be conducted in 70-75% yield with sodium-ethanol in THF (modified Bouveault-Blanc reduction). The substrates (2) are obtained by Wolff rearrangement of a-acyl-a-benzyl-sulfonyldiazomethanes (1).1... 

Silver benzoate in methanol is also the catalyst of choice for the classical homologation of cr-amino acids (and peptides) to the corresponding f3-amino esters by Wolff rearrangement.353 An interesting application in natural... 

The acid was then converted to its acid chloride (XXXVII), thence to the diazoketone (XXXVIII), and finally to the acid (XXXIII) by Wolff rearrangement as shown below. Its endo configuration and the structures of the epimeric acids obtained in the Wittig reaction sequence are thereby established. 

SCHEME 12.1 Photochemical reactions of diazonaphtoquinone derivatives elimination of molecular nitrogen with formation of a carbene, followed by Wolff rearrangement to give a ketene that reacts with water traces to form a carboxylic acid. 

The lactam product 13 is formed by Wolff rearrangement of the carbene generated from the diazoketone 12 and silver(I), followed by intramolecular trapping of the intermediate ketene by the tosylamine group. See Scheme 4.101 and J. Wang and Y. Hou, J. Chem. Soc., Perkin Trans. 1 (1998), 1919. 

A stable silyl-substituted ferrocenyl-ketene has been generated by Wolff rearrangement (Scheme 7.44). This ketene with the bulky silyl group is less reactive toward n-butylamine than the parent ferrocenyl-ketene by a factor of 7 x 10, showing the steric protection provided by the large substituents. 

Scheme 3.21 Domino rearrangement route to pyrroles initiated by Wolff rearrangement of g-diazo-p-oximino enones.

The 2-carboxamidophenyl ketene 261 formed by Wolff rearrangement of 260 can be cyclized to 262 (Scheme 83) (1992JCS(P1)2845). 

The methyl(dimethylvinyl)ketene 428 is generated via irradiation of a parent diazoketone 426 or by Wolff rearrangement of the 5-acyl-3,3-dimethyl-3H-pyrazoles 427. Upon irradiation in an inert solvent, 428 is submitted cycloaddition to diazacyclopentadiene to afford the [4 + 2] adduct 429 in good yield via nucleophilic addition (Scheme 131) (1973JCS(CC) 247, 1973TL2875). 

Thermolysis of N,N-dialkyldiazoacetamides in matrices results in formation of ketenes by Wolff rearrangement, as well as competitive formation of C—H insertion products, with ketenes favored for cyclic precursors. Matrix photolysis in argon of 65 forms an unobserved carbene, which leads mainly to the P-lactam 66 and small amounts of the ketene 67 as identified by IR spectroscopy (Eqn (4.34)). Photolysis of 65 in a CO matrix gives capture of the carbene by CO forming ketene rotational isomers syn-68 and anti-68, similarly identified by IR spectroscopy (Eqn (4.35)), while N,N-dimethyl and N,N-diethyl diazoamides form insertion products. ... 

A systematic study of amine reactions with ring-substituted arylketenes ArCH=C=0 (175) generated by Wolff rearrangements included measurements of ketene infrared stretching frequencies, which varied from 2197 to 2117 cm, but even with this relatively small variation gave a distinct correlation with the substituent a values (Eqn (4.115)). ... 

Acylketenes generated by Wolff rearrangement undergo uncatalyzed Friedel-Crafts type reactions with different nitrogen heterocycles, including N-methylpyrrole, as in the example shown (Eqn (4.126)). The acylation was also successful with dihydrofuran and dihydropyran. At higher temperatures ketene dimerization also occurred. 

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