Carbonyl ylides, aryl

More recently carbonyl ylides and the corresponding imino ylides generated from aryl- and vinyldiazoacetates have been shown to undergo a variety of processes not previously encountered (Scheme 12) [112,113]. The difference in... 

Efforts to realize an intramolecular version of the above reactions met with limited success when monocyclic 4-thio-substituted (3-lactams were used. Cu(acac)2-catalyzed decomposition of diazoketone 358 produced the epimeric carbapenams 359 a, b together with the oxapenam derivative 360 341 these compounds correspond to the C4/S insertion products obtained in intermolecular reactions. Oxapenams were obtained exclusively when the acrylate residue in 359 was replaced by an aryl or heteroaryl substituent 275 342). The different reaction mode of diazoketones 290a, b, which furnish mainly or exclusively carbonyl ylide rather than sulfur ylide derived products, has already been mentioned (Sect. 5.2). 

Laser flash photolysis of 18 (Ar = -N02C6H4) led to the formation of the aryl chlorocarbene detected at 320 nm. In the presence of acetone, a new species was observed at X = 590 nm that was assigned the structure of carbonyl ylide 19. The ylide, formed by attack of acetone on the carbene, was shown to be irreversible, where the lifetime of the ylide (1.35 ps, fecyciization = 7.40 x 10 s ) was controlled by cyclization to the aryl epoxide 22. The rate constant for the cycloaddition of substituted benzaldehydes to produce dehydrodioxolane (21) was determined experimentally (e.g., p-ClPhCHO=6.16 x 10 M s ). 

Dittami et al. (170,171) was able to generate a carbonyl ylide via photocycliza-tion of an aryl vinyl ether (Scheme 4.85). The photocyclization proceeded through a six-electron rearrangement providing initially the carbonyl ylide, then subsequent to the cyclization, a dipolar cycloaddition takes place with a pendant olefinic tether. 

There are very few examples of photolysis being used for preparation of a carbonyl ylide. The Dittami protocol follows work completed from his lab with aryl vinyl sulfides. Photolysis, followed by cycloaddition, led to the cycloadduct 305 in excellent yield and stereoselectivity. If the aryl vinyl ether 304 was subjected to irradiation in a mixed solution of toluene-methanol at 366 nm rather than a single solvent of toluene, cyclized product was obtained, but no cycloadduct was formed. If a simple phenyl aryl ether was subjected to the same tandem conditions, the cyclized product was generated, but no cycloadduct was detected. 

The carbonyl ylide generated from metal carbene can also add to C=0 or C=N bonds. The [2 + 3]-cycloaddition of carbonyl ylide with G=0 bond has been used by Hodgson and co-workers in their study toward the synthesis of zaragozic acid as shown in Scheme n 27a,27d Recently, a three-component reaction approach to syn-a-hydroxy-f3-amino ester based on the trapping of the carbonyl ylide by imine has been reported.The reaction of carbonyl ylide with aldehyde or ketone generally gives l,3-dioxolanes. Hu and co-workers have reported a remarkable chemoselective Rh2(OAc)4-catalyzed reaction of phenyl diazoacetate with a mixture of electron-rich and electron-deficient aryl aldehydes. The Rh(ii) carbene intermediate reacts selectively with electron-rich aldehyde 95 to give a carbonyl ylide, which was chemospecifically trapped by the electron-deficient aldehyde 96 to afford 1,3-dioxolane in a one-pot reaction (Equation (12)). 

The 2,4,6-triphenylpyrylium terafluoroborate (TPT)-sensitized electron transfer of aryl-substituted epoxides such as 250 leads to ring opening via selective C—O bond cleavage, while subsequent [3 + 2]-cycloaddition of the resultant carbonyl ylide with electron-rich olefins 251 leads to the synthesis of substituted THF derivatives 252 and 253 (Scheme 8.69) [109]. 

Thermal and photochemical cycloadditions of a variety of aryl oxiranes with electron-deficient cycloaddends have been described <90JCS(P1)153, 90JCS(P1)159, 90JCS(Pl)ll93>. These reactions give five-membered cycloadducts by way of cycloaddition across the oxirane C—C bond, presumably via a carbonyl ylide (Scheme 50). 

Finally, carbenoid species can be used as the carbon donor in aldehyde epoxidations. Thus, the rhodium carbenoid derived from the cyclic diazoamide 49 and rhodium(II) acetate reacts stereo selectively with aryl aldehydes to provide spiro-indolooxiranes 50 with Z-stereochemistry. The reaction is believed to proceed via the formation of a carbonyl ylide 51, which undergoes stereospecific thermal conrotatory electrocyclization to form the observed epoxide <04SL639>. 

A review of the methods for the generation of cyclic carbonyl ylides from intramolecular carbene additions has recently appeared [64]. This intermediate was first exploited as the An component for cycloaddition reactions by Ibata [65]. ort/io-Disubstituted carboalkoxy aryl diazoketones such as 54 were decomposed by copper complexes, generating six-membered ring carbonyl ylides. These transient intermediates underwent subsequent intermolecular cycloadditions in the presence of ethylenic and acetylenic reagents to give predominantly exo products containing the oxabicyclo[3.2.1] nucleus, Eq. 38. 

Padwa subsequently described some intramolecular versions of this reaction. A structurally similar aryl ester, 55, a tethered to a terminal olefin was subjected to rhodium-catalyzed diazo decomposition. Carbonyl ylide formation followed by intramolecular cycloaddition resulted in tricyclic product 56 a, Eq. 39 [66 - 69]. Cycloaddition also occurred with the amide analogue 55 b. 

The spirodioxolane 32 was synthesized in moderate to good yield [74] from a similar three-component reaction involving diazo ester, aryl aldehyde and p-benzoquinone. Here, p-benzoquinone acts as the dipolarophile to trap the intermolecular carbonyl ylide generated from 13 and the aldehyde (Scheme 10). 

A series ofQ -diazo-/9-(o-carbomethoxy)-substituted aryl ketones were prepared and employed as model systems for a synthetic approach towards the alkaloid, ribasine (114) [116]. The six-membered ring carbonyl ylide dipoles were generated from the o-allyl-substituted diazo ketoester 112 and Rh2(OAc)4 to access the cycloadduct 113 (Scheme 35). This result constitutes a promising model study towards the synthesis of the alkaloid, ribasine (114). 

Multicomponent reactions, which have been known for over 150 years, are those chemical transformations in which more than two reactants combine in a sequential manner to give highly selective products that retain majority of the atoms of the starting materials [36]. Because of the inherent molecular diversity, efficiency, and atom economy, they are highly sought after by chemists and have been widely used in the synthesis of some heterocyclic compounds. Hu and coworkers reported one unique example wherein the electron-rich aryl aldehydes selectively formed a carbonyl ylide with phenyldiazoacetate, which successively cyclized with electron-deficient aryl aldehydes to give the dioxolane (Scheme 2.22) [37]. 

Scheme 2.22 Three-component reaction of carbonyl ylide with aryl aldehydes.

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