Oxonium Ylide Research Articles

Ammonium, Oxonium and Sulfonium Ylides—Generation of Sulfur Ylides from Metal Carbenoids

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Ammonium, Oxonium and Sulfonium Ylides—Generation of Ammonium Ylides by Desilylation of α‐Silyl Ammonium Salts

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Ammonium, Oxonium and Sulfonium Ylides—Generation of Sulfonium Ylides from Carbenes and Carbenoids

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Ammonium, Oxonium and Sulfonium Ylides—Generation of Sulfonium Ylides by Desilylation of α‐Silyl Sulfonium Salts

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A Concise and Stereoselective Synthesis of the A-Ring Fragment of the Gambieric Acids

The A-ring fragment of the gambieric acids has been prepared by a short and efficient route. The key 3(2H)-furanone intermediate has been obtained by [2,3] rearrangement of an allylic oxonium ylide generated from intramolecular reaction of a crotyl ether with a copper carbenoid. A single stereogenic center has been set by using a chiral pool starting material and the other three have been established by using highly diastereoselective substrate-controlled transformations. [reaction--see text]

Catalyst and ring size effects on periselectivity of oxonium ylide rearrangements.

Diazoketones were subjected to carbene-transfer with Rh(II) or Cu(II) catalysts to probe the selectivity for rearrangement via five- or six-membered oxonium ylides. 4,5-Bis(benzyloxy) and 4-allyloxy-5-benzyloxy substrates 3a,b showed a large preference for rearrangement via the five-membered ylide under all conditions. However, a sharp divergence was seen with 5-allyloxy-4-benzyloxy substrate 3c, which underwent predominantly a [2,3]-shift to pyran 5c via the six-membered ylide with Cu(II) catalysis and a [1,2]-shift to furan 4c via the five-membered ylide with Rh(II) catalysis.

3 + 2] Cycloreversion of bicyclo[m.3.0]alkan-3-on-2-yl-1-oxonium ylides to alkenyloxyketenes. Stereospecific aspect.

Rhodium(II)-catalyzed intramolecular reaction of diazoketones 1 bearing a cyclic ethereal moiety transiently formed bicyclo[m.3.0]octan-3-one-1-oxonium-2-ylides (2), which underwent sigmatropic and stereospecific [3 + 2] cycloreversion reaction to form alkenyloxyketenes 3. The ketenes were efficiently trapped by methanol to form the corresponding esters 4. Mechanistic studies revealed that the size of ethereal ring can be variable at least from THF to the THP, oxepane, and oxocane moiety, i.e., m = 3-6. On the other hand, the size of the ylide ring containing the carbonyl unit is limited to a five-membered ring. The cycloreversion was found to be stereospecific as was proven by the reactions of diastereoisomeric pairs bearing a methyl group at the bond-cleaving position. From threo isomers 7, (E)-alkenyloxyacetates 15 were exclusively formed (77-84%), whereas from erythro isomers 8, (Z)-isomers 16 were formed (80-88%). Mechanism of the cleavage from diazoacetonyl-substituted cyclic ethers to alkenyloxyketenes via bicyclic oxonium ylides was analyzed on the basis of calculations employing the hybrid density functional B3LYP and the highly correlated quadratic configuration interaction QCISD method to reveal that the concerted [3 + 2] cycloreversion is the key step of this reaction.

Stereoselective Synthesis of Tetrahydropyran‐3‐ones by Rearrangement of Oxonium Ylides Generated from Metal Carbenoids.

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Competing Formations of Oxonium and Carbonyl Ylides with Carbonylcarbenes.

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Carbon-carbon bond formation reaction of ethereal oxonium ylides via metal-enolate intermediates.

First, the carbon-carbon (C-C) bond-forming reaction of aldehydes with bicyclo[m.n.0]-1-oxonium ylides was studied as the ylide was transiently formed in the Rh(II)-catalyzed reaction of a nonenolizable diazoketone, namely, 2-(3-diazo-1,1-dimethyl-2-oxopropyl)-2-methyldioxolane (1). The reaction of 1 with benzaldehyde in the presence of ClTi(Oi-Pr)3 gave the three-carbon, ring-enlarged, and C-C-bonded product 2a (53%). Second, enolizable diazoketone 5 bearing no methyl substituents at the alpha-position was studied under similar catalytic conditions, and the ring-enlarged and C-C-bonded products 19a and 20a were also formed (87%) when titanium compound ClTi(Oi-Pr)3 or Ti(Oi-Pr)4 was used. Similar reactions of diazoketones 27, 29, and 31 bearing a cyclic acetal ring and a longer tethering chain than 5 gave C-C-bonded products 28 (74%), 30 (8%), and 32 and 33 (overall 48%), respectively, albeit 28 and 30 possessed a spiro bisacetal structure. Thus, the hitherto unclarified C-C bond formation of ethereal oxonium ylides with carbonyl electrophiles was realized with the use of an appropriate Lewis acid, for example, ClTi(Oi-Pr)3.

Cyclooctanoid ring systems from mixed acetals via heteroatom-assisted [1,2]-shift of oxonium ylides.

Cyclic mixed acetals with pendant diazoketone side chains undergo efficient rearrangement to ether-bridged cyclooctanoid systems upon treatment with Cu(hfacac)2. This result demonstrates that heterosubstituted carbons are suitable migrating groups for the Stevens [1,2]-shift of oxonium ylides. In the case of a mixed thioacetal, the resulting sulfide served as a trigger for cleavage of the bridging ether through one of two complementary strategies, furnishing a bicyclo[6.3.0]octene product with an angular hydroxyl group.

Competing Formations of Oxonium and Carbonyl Ylides with Carbonylcarbenes

AbstractA series of 2‐mono‐ and 2,2‐disubstituted 1,3‐dioxepin derivatives, two of which also had a carbonyl function in one of their 2‐R groups, were prepared and reacted with dimethyl diazomalonate with copper(II) acetylacetonate as a catalyst. Ylide formation probabilities with allyl ether and/or carbonyl functions were investigated. A chemoselectivity in favor of carbonyl ylide was observed.

Stereoselective synthesis of tetrahydropyran-3-ones by rearrangement of oxonium ylides generated from metal carbenoids

The synthesis of tetrahydropyran-3-ones by copper-catalysed reactions of diazo ketone tethered allylic ethers has been explored. Product distribution can be explained by the intermediacy of a free ylide or direct rearrangement of a metal-bound ylide equivalent.

ChemInform Abstract: Cyclic Oxonium Ylides: Building Blocks for Iterative Synthesis of Polycyclic Ethers.

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An oft-studied reaction that may never have been: direct catalytic conversion of methanol or dimethyl ether to hydrocarbons on the solid acids HZSM-5 or HSAPO-34.

Using highly purified reagents and careful tests, we show that methanol and dimethyl ether are apparently unreactive on the two most important methanol-to-hydrocarbon catalysts, HZSM-5 and HSAPO-34. Thus, none of the "direct" mechanisms involving two to four carbon atoms in intermediates such as oxonium ylides, carbenes, carbocations, and free radicals are applicable. Only the "indirect" route (hydrocarbon pool) is an established mechanism for this chemistry. An active catalyst requires a hydrocarbon pool that typically begins with products from organic impurities in the feed, carrier gas, or the solid acid itself. Impurities may also play important roles in other reactions catalyzed by solid acids.

ChemInform Abstract: Diels—Alder Adducts of Medium‐Ring Carbocyclic Dienes Prepared by Rearrangement of Catalytically Generated Cyclic Oxonium Ylides

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Electronic Effects in Migratory Groups. [1,4]‐ versus [1,2]‐Rearrangement in Rhodium Carbenoid Generated Bicyclic Oxonium Ylides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Cyclic oxonium ylides: building blocks for iterative synthesis of polycyclic ethers

A series of diazoketones bearing remote benzyl or allyl ethers was subjected to a variety of conditions for catalytic diazodecomposition and cyclic oxonium ylide formation as a possible method for polycyclic ether synthesis. Allyl ethers 19 , 25 and 29 underwent efficient conversion to the corresponding bis(pyran) and tris(pyran) products in the presence of Cu(tfacac) 2, while benzyl ether 15 was converted to bicyclic products 16 and 34 with Rh 2(tpa) 4. Treatment of homologous substrate 32 with Rh 2(tpa) 4 provided novel medium-ring cyclopropanation products 35 in good yield.

Enantioselective tandem formation and [2,3]‐sigmatropic rearrangement of cyclic propargylic oxonium ylides catalyzed by dirhodium(II) tetrakis[N‐phthaloyl‐(S)‐tert‐leucinate

AbstractThis paper describes the first examples of catalyst‐dependent asymmetric induction in the periselective [2,3]‐sigmatropic rearrangement of propargylic oxonium ylides generated by catalytic diazo decomposition. Catalysis of α‐diazo‐ß‐keto esters 4a—g using dirhodium(II) tetrakis[N‐phthaloyl‐(S)‐tert‐leucinate] in toluene has led to the virtually exclusive formation of benzofuran‐3‐ones bearing an allenic group with up to 79% ee.

Diels-Alder adducts of medium-ring carbocyclic dienes prepared by rearrangement of catalytically generated cyclic oxonium ylides.

The novel bicyclic and tricyclic systems dimethyl (4aS*,6S*)-6-methoxy-7-oxo-4a,5,6,7,8,9-hexahydro-2H-benzocycloheptene-3,4-dicarboxylate, C(16)H(20)O(6), (I), dimethyl (4aS*,6R*)-6-methoxy-7-oxo-4a,5,6,7,8,9-hexahydro-2H-benzocycloheptene-3,4-dicarboxylate, C(16)H(20)O(6), (II), (3aS*,9R*,10aS*,10bR*)-9-methoxy-2-oxa-1,3a,4,6,7,8,9,10,10a,10b-decahydro-3H-cyclohepta[e]indene-1,3,8-trione, C(14)H(16)O(5), (III), and (1S*,2R*,9S*,10aR*)-9-methoxy-8-oxo-1,2,3,5,6,7,8,9,10,10a-decahydrobenzocyclooctene-1,2-dicarboxylic acid, C(15)H(20)O(6), (IV), have been crystallographically characterized, allowing the determination of the relative configuration of the stereogenic centres. The poor quality of the dicarboxylic acid crystals necessitated the use of synchrotron radiation.