Carbonyl ylides reaction

The intermolecular version of the above described reaction has also been reported [92]. In the first example the reaction of a rhodium catalyst carbonyl ylide with maleimide was studied. However, only low enantioselectivities of up to 20% ee were obtained [92]. In a more recent report Hashimoto et al. were able to induce high enantioselectivities in the intermolecular carbonyl ylide reaction of the... 

Transition-metal mediated carbene transfer from 205 to benzaldehyde generates carbonyl ylides 211 which are transformed into oxiranes 216 by 1,3-cyclization, into tetrahydrofurans 212, 213 or dihydrofurans 214 by [3 + 2] cycloaddition with electron-deficient alkenes or alkynes, and 1,3-dioxolanes 215 by [3 + 2] cycloaddition with excess carbonyl compound120 (equation 67). Related carbonyl ylide reactions have been performed with crotonaldehyde, acetone and cyclohexanone (equation 68). However, the ylide generated from cyclohexanone could not be trapped with dimethyl fumarate. Rather, the enol ether 217, probably formed by 1,4-proton shift in the ylide intermediate, was isolated in low yield120. In this respect, the carbene transfer reaction with 205 is not different from that with ethyl diazoacetate121, whereas a close analogy to diazomalonates is observed for the other carbonyl ylide reactions. 

Scheme 8. Carbonyl ylide reactions derived from 10a...

Rhodium-generated bicyclic six-membered ring carbonyl ylides from the diazo ketone 158 with p-quinones have also been studied to yield interesting oxygen heterocycles [133]. In line with the five-membered ring carbonyl ylide reactions (see Sect. 2.1), the a-diazocarbonyl compound 158 furnished oxygen-rich heterocyclic systems 161-163 (Scheme 52). 

The parallel ability of oxiranes to undergo ring opening to carbonyl ylides was first noted in the case of tetracyanooxirane (68T2551), but such reactions have not been widely exploited. The addition to alkenes, leading to formation of tetrahydrofurans, is stereospecific (Scheme... 

Generation and reactions of carbonyl ylides, nonstabilized 1,3-dipolar reagents 98YGK681. 

For the reactions of other 1,3-dipoles, the catalyst-induced control of the enantio-selectivity is achieved by other principles. Both for the metal-catalyzed reactions of azomethine ylides, carbonyl ylides and nitrile oxides the catalyst is crucial for the in situ formation of the 1,3-dipole from a precursor. After formation the 1,3-di-pole is coordinated to the catalyst because of a favored chelation and/or stabiliza-... 

For azomethine ylides and carbonyl ylides, the diastereoselectivity is more complex as the presence of an additional chiral center in the product allows for the formation of four diastereomers. Since the few reactions that are described in this chapter of these dipoles give rise to only one diastereomer, this topic will not be mentioned further here [10]. 

The rhodium-catalyzed tandem carbonyl ylide formation/l,3-dipolar cycloaddition is an exciting new area that has evolved during the past 3 years and high se-lectivities of >90% ee was obtained for both intra- and intermolecular reactions with low loadings of the chiral catalyst. 

Rhodium Catalysts for Reactions of Carbonyl Ylides 242 Conclusion 244 Acknowledgment 245 References 245... 

Carbonyl ylides continue to be targets of opportunity because of their suitability for trapping by dipolar addition. High enantiocontrol has been achieved in the process described by Eq. 16 [109], but such high enantioselectivity is not general [110] and is dependent on those factors suggested by Scheme 11. Using achiral dirhodium(II) catalysts, Padwa and coworkers have developed a broad selection of tandem reactions of which that in Eq. 17 is illustrative [111] these... 

The application of 1,3-dipolar cycloaddition processes to the synthesis of substituted tetrahydrofurans has been investigated, starting from epoxides and alkenes under microwave irradiation. The epoxide 85 was rapidly converted into carbonyl ylide 86 that behaved as a 1,3-dipole toward various alkenes, leading to quantitative yields of tetrahydrofuran derivatives 87 (Scheme 30). The reactions were performed in toluene within 40 min instead of 40 h under classical conditions, without significantly altering the selectivi-ties [64]. 

Nonstabilized carbonyl ylides (41) prepared by reaction of a-iodosilyl ethers with Smlj, can be trapped with various alkenes, alkynes and allenes to form furans of type 42, 43, and 44... 

Among other olefins prepared in conventional ylide reactions with carbonyls are (68), (69), (70), and (71). ... 

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). 

Diels-Alder reaction of the 1,3,4-oxadiazole with the pendant olefin and loss of N2, the C2-C3 7t bond participates in a subsequent 1,3-dipolar cycloaddition with the carbonyl ylide to generate complex polycycles such as 45 as single diastereomers with up to six new stereocenters. That the cascade reaction is initiated by a Diels-Alder reaction with the alkene rather than with the indole is supported by the lack of reaction even under forcing conditions with substrate 46, in which a Diels-Alder reaction with the indole C2-C3 n bond would be required [26a]. 

Scheme 29. 1,3-DC Reactions of porphyrin la with a carbonyl ylide.

Finally, it is important to mention that there are other related publications in which porphyrin macrocycles are not directly used as dipolarophiles but are transformed into new derivatives that can react with carbonyl ylides via ACE (alkene cyclobutene epoxide) reactions. This idea arose in 1997, when Russell and co-workers found that fused ester-activated cyclobutene epoxides 86 can be ring-opened to give carbonyl ylides 87, and that these can be trapped stereospecifically by ring-strained alicyclic dipolarophiles, such as 2,5-norbomadiene, to form hetero-bridged norbomanes 88 in good yields, through ACE transformations (Scheme 31) <97CC1023>. 

Mejla-Oneto and Padwa have explored intramolecular [3+2] cycloaddition reactions of push-pull dipoles across heteroaromatic jr-systems induced by microwave irradiation [465]. The push-pull dipoles were generated from the rhodium(II)-cata-lyzed reaction of a diazo imide precursor containing a tethered heteroaromatic ring. In the example shown in Scheme 6.276, microwave heating of a solution of the diazo imide precursor in dry benzene in the presence of a catalytic amount of rhodium I) pivalate and 4 A molecular sieves for 2 h at 70 °C produced a transient cyclic carbonyl ylide dipole, which spontaneously underwent cydoaddition across the tethered benzofuran Jt-system to form a pentacyclic structure related to alkaloids of the vindoline type. 

A number of benzo- or dibenzo-fused seven membered phosphorus heterocyclic systems have also been studied. These include the benzo-fused oxa-bridged phosphaalkene 76 prepared by thermolysis of 2,3-diphenylindenone 23-epoxide (as a source of the carbonyl ylide 1,3-dipole intermediate) in the presence of /-butylphosphaalkyne. This bridged phosphaalkene is unusually stable even without inert gas blanketing . Reaction of 76 with sulfur or grey selenium stereoselectively affords the thia- or selenaphosphiranes 77 (X = S, Se respectively). <00T6259>... 

Reactions of 1,1-difluoropropadiene or monofluoropropadiene and a 1,3-dipolar reagent such as diazo compounds, nitrones, nitrile oxides and carbonyl ylides are an excellent route to five-membered heterocycles, such as 126 and 127 [61-63]. 

Reactions.—Nucleophilic Attack at Carbon. (/) Carbonyls. Methyl arylglyoxylates react with trisdimethylaminophosphine (TDAP) to form m-a/S-dimethoxycarbonyl-stilbene oxides.63 The initially formed zwitterion (61) reacts with a second molecule of the ester to form a fra/ -diphenyl-1,4,2-dioxaphospholan intermediate, which undergoes a concerted symmetry-allowed retrograde n2s + 4 cycloaddition to give a carbonyl ylide, conrotatory cyclization of which leads to the cw-oxirans (62) (Scheme 3). 

C6 and C9 are at opposite ends of a four-carbon unit, but since one of these atoms (C7) is saturated and quaternary, a Diels-Alder reaction is unlikely (can t make diene). The combination of a diazo compound with Rh(II) generates a carbenoid at C9. The nucleophile 06 can add to the empty orbital at C9, generating the 06-C9 bond and a carbonyl ylide at C6-06-C9. Carbonyl ylides are 1,3-dipoles (negative charge on C9, formal positive charge on 06, electron deficiency at C6), so a 1,3-dipolar cycloaddition can now occur to join C2 to C6 and Cl to C9, giving the product. Note how a relatively simple tricyclic starting material is transformed into a complex hexacyclic product in just one step ... 

Cyclodditions to Carbonyl Derivatives. Electrophilic transient carbenes are known to react with carbonyl derivatives through the oxygen lone pair to give carbonyl ylides 26.43 These 1,3-dipolar species are usually characterized by [3 + 2]-cycloaddition reactions or can even be isolated44 a small amount of the corresponding oxiranes is sometimes obtained.433,45 To date, no reaction of transient nucleophilic carbenes with carbonyl derivatives has been reported. 

The intramolecular addition of acylcarbene complexes to alkynes is a general method for the generation of electrophilic vinylcarbene complexes. These reactive intermediates can undergo inter- or intramolecular cyclopropanation reactions [1066 -1068], C-H bond insertions [1061,1068-1070], sulfonium and oxonium ylide formation [1071], carbonyl ylide formation [1067,1069,1071], carbene dimerization [1066], and other reactions characteristic of electrophilic carbene complexes. 

Some examples of transformations involving carbonyl ylides are listed in Table 4.20. Entry 1 illustrates the conversion of P-acyloxy-a-diazoesters into a-acyloxyacrylates by ring fission of a cyclic carbonyl ylide [978]. This reaction has been used for the synthesis of the natural aldonic acid KDO (3-deoxy-Z)-manno-2-octulosonic acid), which is an essential component of the cell wall lipopolysaccharide of gram-negative bacteria (Figure 4.15). 

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