A-diazo ketone decomposition

The cycloaddition reaction of dipoles has been known since the 18th century, later, Huisgen introduced the concept of a 1,3-dipole [30]. One of the earhest examples of copper(II) acetylacetonate [Cu(acac)2] catalyzed 1,3-dipole formation involved the controlled decomposition of an a-diazo ketone [31]. Some cases utilized copper as the metal species and demonstrated the feasibility of cycloaddition reactions and these 1,3-dipoles with dipolarophiles. These reactions set the stage for the evaluation of additional transition metals capable of catalyzing this transformation. The earliest example of rhodium(II)-catalyzed a-diazo ketone decomposition to form a 1,3-dipole was described by Teyssie and co-workers [32]. Despite this promising beginning, it was not until many years later that rhodium(II) was used generally for the formation of such 1,3-dipoles [6-12,21,29,30] (Fig. 1). 

Any heterocycle containing the OCH=CH moiety can in principle extrude the superfluous fragment and form oxirene, as illustrated for a five-membered ring in Scheme 105. Probably the most propitious AB fragment would be nitrogen, but the required 1,2,3-oxadiazole (123) is unknown (see Chapter 4.21), probably because of ready valence tautomerization to diazoethanal (Scheme 106) (this approach has been spectacularly successful with the sulfur analogue of (2) (8UA486)). The use of (123) as an oxirene precursor is thus closely linked to the important diazo ketone decompositions discussed in Section 5.05.6.3.4(f). 

An a-diazo ketone 1 can decompose to give a ketocarbene, which further reacts by migration of a group R to yield a ketene 2. Reaction of ketene 2 with water results in formation of a carboxylic acid 3. The Woljf re arrangement is one step of the Arndt-Eistert reaction. Decomposition of diazo ketone 1 can be accomplished thermally, photochemically or catalytically as catalyst amorphous silver oxide is commonly used ... 

A regio- and stereospecific synthesis of modhephene has also been achieved beginning with the Weiss-Cook reaction As illustrated in Scheme XCVII, cyclo-pentai -l,2-dione can be readily crait l into a-diazo ketone 8(M), copper-catalyz l decomposition of which delivers tricyclic ketone 801. Following the dimethylation of this intermediate, carbomethoxylation was accomplished to give 802 and provide... 

The earliest methods for preparing cyclic a-diazo ketones involved the oxidation of the monohydrazones prepared from a-diketones, generally using mercuric oxide.7,8 Recent modifications of this procedure include the use of calcium hypochlorite in aqueous sodium hydroxide or activated manganese dioxide as oxidants.1 The latter reagent, especially, hoc ms preferable to mercuric oxide. The base-catalyzed decomposition of tile monotosylhydrazoneH of a-diketones has been... 

The cyclopropanation of alkenes, alkynes, and aromatic compounds by carbenoids generated in the metal-catalyzed decomposition of diazo ketones has found widespread use as a method for carbon-carbon bond construction for many years, and intramolecular applications of these reactions have provided a useful cyclization strategy. Historically, copper metal, cuprous chloride, cupric sulfate, and other copper salts were used most commonly as catalysts for such reactions however, the superior catalytic activity of rhodium(ll) acetate dimer has recently become well-established.3 This commercially available rhodium salt exhibits high catalytic activity for the decomposition of diazo ketones even at very low catalyst substrate ratios (< 1%) and is less capricious than the old copper catalysts. We recommend the use of rhodium(ll) acetate dimer in preference to copper catalysts in all diazo ketone decomposition reactions. The present synthesis describes a typical cyclization procedure. 

In the first case, there is probably an initial reaction of the dithiolethione with the acylcarbene resulting from the thermal decomposition of a diazo ketone (equation 22). 

Spiroannelatwn of phenolic a-diazoketones (8, 118-119). The Cu(I) decomposition of the phenolic a-diazo ketone 1 has been used for a synthesis of a-chamigrene (3). ... 

RCH=C=0, except when these are generated in situ by decomposition of a diazo ketone (the Wolff rearrangement, 18-8) in the presence of the imine. It has been done with ketene, but the more usual course with this reagent is an addition to the enamine tautomer of the substrate. Thioketenes ° (R2C=C=S) give p-thio-Imines also form p-lactams when treated with (i) zinc (or another... 

Intramolecular cyclopropanation of olefinic a-diazo ketones and a-diazo esters has been widely used in organic synthesis. When a carbenoid center and the double bond are separated by a chain of three atoms, one of which is oxygen, a five-membered O-containing heterocycle is formed. Intermolecular cyclopropanations of olefins are known to allow stereospecific formation of desired products. Thus, decomposition of substituted allyl diazomalonates 265 in the presence of copper salts gives rise to bicyclic... 

Padwa and co-workers (89TL2633 93JA2637) have elaborated an elegant modification of the cyclization/cycloaddition approach that involves the displacement of a carbene center and provides access to O-bridged compounds with an indenone moiety. An illustrative example is the synthesis of compound 718 through the Rh(II)-catalyzed decomposition of a-diazo ketones bearing tethered alkyne units in the presence of a dipolarophile (91JOC2523). 

Ketocarbenes of type (21) obtained from acyclic and medium to large ring alicyclic a-diazo ketones (20) are prone to react by way of an intramolecular [1,2] H-shift, especially under catalytic conditions, to afford a, 3-unsaturated ketones (22). °4 -60 Pranzen has shown that the Wolff rearrangement of diazo ketones (20) is favored if temperatures in excess of 100 °C are used in the photochemical or Ag20-pro-moted decompositions. Related [1,2] methyl shifts can also occur, and this pathway is the principal decomposition route of 4-diazo-2,2,5,5-tetramethyl-3-hexanone. ... 

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