Ylide Intermediates Research Articles

Ring-expansion of thioacetal ring via bicyclosulfonium ylide. Effect Of protic nucleophile on ylide intermediate

The reaction of 2-(3-diazo-2-oxopropane-1-yl)-2-methyldithiolane 9a, 2-(4-diazo-3-oxobutane-2-yl)-2-methyldithiolane 9c, and 2-(3-diazo-2-oxopropane-1-yl)-2-methyl-1,3-dithiane 9b with Rh(2)(OAc)(4) gave three-carbon ring-expansion products dithiocan-2-en-1-ones 13a, 13c and dithionan-2-en-1-one 13b, respectively. 2-(5-Diazo-4-oxopentyl)-2-methyldithiolane 9e also gave the five-carbon ring-expansion products dithionan-3-en-1-one 13e and 5-methylenedithionane-1-one 13'e. On the other hand, reaction of 2-(4-diazo-3-oxobutyl)-2-methyldithiolane 9d in the presence of AcOH gave the four-carbon ring-expansion product 16d substituted by an acetoxyl group. In addition, the reaction of 2-(3-diazo-2-oxopropyl)-2-methyl-3-oxathiolane 9f in the absence of AcOH gave 4-oxa-7-thiocan-2-en-1-one 19 via a sulfonium ylide intermediate, whereas, in the presence of AcOH, an alternative regioisomer 20 was also formed competitively with 19 via an oxonium ylide intermediate.

The chemistry of vicinal tricarbonyls. Formation of oxomalondiamides

Oxomalondiamides and related systems are readily formed from derivatives of oxalic acid monoamides. The monoamides are converted to labile triacyl nitriles through cyano ylide intermediates for further coupling with amines and other nucleophiles.

Reactions of (Chloromethyl)platinum(II) Derivatives with Nucleophiles. Formation of (Dimethylamino)carbene Complexes UsingN,N,N‘,N‘-Tetramethylmethanediamine as Nucleophile and the X-ray Crystal and Molecular Structures ofcis-[(Ph3P)Pt(CH2NMe3)Cl2],cis(C,P)-[(Ph3P)Pt(CH2CH2C(O)NMe2)Cl], andtrans(As,CH2)-[(Ph3As)Pt(CHNMe2)(CH2NHMe2)Cl]PF6

Reaction, in chloroform solution, of (COD)Pt(CH2Cl)Cl (5) with Me2NCH2NMe2 in the presence of 1 equiv (vs 5) of a monodentate ligand L (L = Ph3P, (p-MeOC6H4)3P, (p-FC6H4)3P, Et3P, Ph3As) gives the (dimethylamino)carbene complexes cis-[LPt(CHNMe2)Cl2] (1a−e) via the cyclic ylide intermediates [LPt(CH2NMe2CH2NMe2)Cl]Cl (2a−e). Major byproducts of the reaction are the (trimethylammonio)methyl ylide complexes cis-[LPt(CH2NMe3)Cl2] (11a−e). With L = Ph3As, carbene product 1e is accompanied by a second carbene complex, trans(As,CH2)-[(Ph3As)Pt(CHNMe2)(CH2NHMe2)Cl]Cl (25). When the reaction with L = Ph3P is carried out in acetonitrile, the amide chelate [(Ph3P)Pt(CH2CH2CONMe2)Cl] (24) is formed in addition to 1a and 11a. A deuterium labeling experiment indicates that formation of 24 involves condensation of a CH2Cl (or derived) moiety with a molecule of solvent. The structures of complexes 11a and 24, and of the hexafluorophosphate analogue (26) of complex 25, have been confirmed by X-ray crystallographic analys...

Tandem Cyclization and Aromatization of Sulfur Bridged Diallenic Systems: Potential Enediyne Models

The synthesis and base catalyzed rearrangement of bis-γ-phenylpropargyl sulfone, sulfoxide and sulfonium salts are described. In contrast to the first two compounds which undergo a fast acetylene to allene isomerization followed by a tandem cyclization and aromatization via a diradical mechanism, the latter compound undergoes a [2,3]-sigmatropic shift via the corresponding ylide intermediate.

Catalysis of chlorosilane on the ring-expansion of cyclic acetals bearing a carbene precursor. Lewis acid–base effect on the oxonium ylide intermediate

Rhodium catalyzed (1–0.1 mol%) decomposition of 2-(3-diazo-2-oxopropyl)-2-methyldioxolane 1a or 2-(3-diazo-1-methyl-2-oxopropyl)-2-methyldioxolane 1b in the presence of a catalytic amount of TMSCl (10 mol%), yielded 4,7-dioxocane 3a (91%) or 3b (49%), whereas similar reaction in the absence of TMSCl caused 1,2-rearrangement to give bicyclobutanones 2a or 2b, respectively; Lewis acid-base catalysis by TMSCl of the ring-expansion of a bicyclooxonium ylide intermediate is revealed.

Efficient synthesis of substituted 1-dimethylamino or 1-methylthio but-3-enylidene-bis-phosphonates, via the [2,3]-sigmatropic rearrangement of related transient ammonium or sulfonium ylides

New variously substituted 1-dimethylamino or 1-methylthio but-3-enylidene-bis-phosphonates have been prepared from readily availableα-dimethylamino or α-methylthio methylene-bis-phosphonates by postulated [2,3]-Wittig rearrangements of the corresponding N- or S-allylic intermediate ylides. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 281–289, 1999

Ligand effects in the metal catalysed reactions of N-aryldiazoamides: Ylide formation vs. insertion reactions

Diazoamides 1a and 1b were prepared from 2-( O-allyl)- and 2-( S-allyl) anilines 2 respectively. Copper(II) catalysed decomposition of 1 resulted in formation of benzofused heterocycles 7 by [2,3]-rearrangement of the intermediate ylide. Rhodium(II) perfluorbutyramide catalysed reaction, however, gave mainly the indoles 8, 9 whereas rhodium(II) acetate catalysed reaction resulted in a mixture of products, with β-lactams formed by intramolecular C-H insertion predominating. Catalysed decomposition of N-pyridyl diazoamide 13 gave the stable pyridinium ylide 14.

Dirhodium(II)-catalyzed carbonyl ylide generation. Stereoelectronic control in dioxolane formation

The combination of ethyl diazoacetate with aryl aldehydes in the presence of copper(I) or rhodium(II) catalysts results in the formation of 1,3-dioxolane products in moderate to good yields. These reactions occur through a pathway that involves ylide intermediates. Catalyst-dependent diastereocontrol is observed and suggests that metal-associated ylides are involved in the product-determining step. The influence of aryl aldehyde substituents has been determined.

New adventures with divalent carbon intermediates

AbstractPart I: Reactions of 3‐substituted 1‐azabicyclo[1.1.0]butanes (1a and 1b) with dichlorocarbene proceed in each case via nitrogen ylide intermediates with concomitant ring opening to afford the corresponding dihaloimines (2a and 2b, respectively). Part II: Vinylidènecarbene‐cycloalkyne equilibria have been studied in three polycarbocyclic systems, i.e., 10a‐10b, 20a‐20b, and 27a‐27b. In all three systems, only the vinylidenecarbene intermediate can be trapped in situ by cyclohexene. The results of site‐specific 13C labeling studies that employ 9‐C(8)‐13CBr2 (enriched with 4 atom‐% 13C), 19‐C(4)‐13CBr2 (enriched with 5 atom‐% 13C), and 23‐C(4)‐13CBr2 (enriched with 10 atom‐% 13C) also support this conclusion and suggest that cycloalkyne intermediates, if formed in these systems, must rearrange very rapidly to the corresponding (thermodynamically favored) vinylidenecarbenes. Part III: Base‐promoted reactions of N‐tosyl‐ and N‐benzhydrylazetidin‐3‐ones (i.e., 30a and 30b, respectively) with diethyl diazomethylphosphonate (DAMP), when performed in the presence of cyclohexene, in each case afford exclusively the product that results via in situ trapping of the corresponding vinylidenecarbene.

Application of (13)C NMR Spectroscopy and (13)C-Labeled Benzylammonium Salts to the Study of Rearrangements of Ammonium Benzylides.

Ylides generated from N-(cyanomethyl)-N,N-dimethyl-N-[alpha-(trimethylsilyl)benzyl]ammonium chloride (4) and fluoride anion afford the products of [1,2] shift 11 and [2,3] shift 13. Formation of product 13 shows that, in the presence of water from TBAF, rearrangements and [1,3]H shift in ylide intermediates become competitive processes. The reaction of N-benzyl-N,N-dimethyl-N-[alpha-(trimethylsilyl)benzyl]ammonium bromide (5) and (13)C labeled (at the benzyl carbon) salt 5 gave a mixture of 10, 14, and 15 as products of [1,4], [1,2], and [2,3] rearrangement, respectively. (13)C NMR spectra of products derived from salt 5 exclude [1,3]H shift in ylide 9a(+-)(). Rearrangement of ylides generated from N-benzyl-N,N-dimethyl-N-[(dimethylphenylsilyl)methyl]ammonium bromide (6) (enriched in (13)C at benzyl carbon) and n-BuLi reveals that N,N-dimethyl-2-[(dimethylphenylsilyl)methyl]benzylamine (20) is not formed by a [1,4] shift but instead, via a [2,3] shift in silylmethylide followed by subsequent [1,4]Si and [1,2]H shift, as previously suggested in the literature. This mechanism is unique to some silyl-substituted ylides.

ChemInform Abstract: Stereodirecting Effects in the Characterization of Ylide Intermediates in Reactions of Singlet Methylene with an Allylic Ether and an Allylic Chloride.

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.

Spiro-fused 2-alkoxy-2-amino-Δ3-1,3,4-oxadiazolines. Synthesis and thermolysis to corresponding aminooxycarbenes

Δ3-1,3,4-Oxadiazolines spiro-fused at C2 to C2 to oxazolidines (12) or to C2 of tetrahydro-1,3-oxazines (13) were synthesized. The oxadiazolines undergo thermolysis in benzene at 90 °C with first-order rate constants of (1.6–50) × 10−5 s−1. The dependence of these rate constants on the nature of the substituents present on the oxadiazoline ring is consistent with a mechanism involving a carbonyl ylide intermediate. Substituents on N of the oxazolidine or tetrahydro-1,3-oxazine moieties play a major role in determining the fragmentation pathways. Oxadiazolines with N-carbonyl groups (12c–j, 13d,e) afford essentially quantitative yields of the corresponding aminooxycarbenes, while other fragmentation reactions compete with carbene generation in the case of oxadiazolines with N-methyl (12b, 13c) or N-sulfonyl (12k) groups. Keywords: nucleophilic carbene, aminooxycarbene, oxadiazoline, oxazolidin-2-ylidene, carbonyl ylide.

Stereodirecting Effects in the Characterization of Ylide Intermediates in Reactions of Singlet Methylene with an Allylic Ether and an Allylic Chloride

The stereodirecting effects of substrate substituents were examined in addition of 1:CH2 to the double bonds of 3-methoxycyclohexene (3a), 3-chlorocyclohexene (3b), and 3-methylcyclohexene (3c) in pentane solution at temperatures from 23°C to −50°C. A preference for addition syn to the directing substituent was observed in reactions of 3a and 3b and was attributed to a reversible interaction of carbene and substituent. In the reaction with 3a this interaction was not obviously ylide formation. © 1997 Elsevier Science Ltd.

Ketene acetals from thermolysis of aryloxy methoxy oxadiazolines. Evidence for carbonyl ylide intermediates

Thermolysis of oxadiazolines (5) in benzene at 110 °C leads to ketene acetals (11) as minor products. Carbonyl ylide intermediates (6), and oxiranes (7), presumably in equilibrium with those ylides, are implicated as unstable precursors of the ketene acetals although none of the oxiranes (carbonyl protected α-lactones) were isolable and only one of the ketene acetals was isolable in pure form. The evidence points to the two-step sequence of thermolysis of oxadiazolines, namely, initial cycloreversion to N2 and carbonyl ylide (6), rather than concerted fragmentation to N2, acetone, and carbene (12). The first-formed ylide does fragment to carbene and acetone in a second step that competes with oxirane formation. A tentative mechanism for reaction of 7 with 12, to afford 11, is advanced. Keywords: carbonyl ylide, dioxy oxirane, ketene acetal, oxadiazoline.

Photochemistry of pyridyl azides and diazo ketones in matrix and in solution

Abstract

Diazo transfer reactions of tosyl azide with carbocyclic β-keto esters: production and decomposition of ring-opened N-tosylcarbamoyl-substituted α-diazo esters

The diazo transfer reaction of tosyl azide 1 with methyl 2-oxocyclopentanecarboxylate 2a, ethyl 2-oxocyclohexanecarboxylate 2b and methyl 2-oxocycloheptanecarboxylate 2c, in the presence of triethylamine, gives ring-opened diazo amido esters 3a–c in fairly high yields. Similar reaction with ethyl 2-oxocyclooctanecarboxylate 2d and methyl camphor-3-carboxylate 2e also leads to the respective diazo esters 3d,e but accompanied by the corresponding azido transfer products 6, 7 to a significant (or major) extent. The thermal, photochemical and rhodium(II) acetate-catalysed decomposition of the novel diazocarbonyl compounds 3a–e has been examined. The results show that intramolecular cyclization onto the N-tosylcarbamoyl substituent can smoothly take place provided that it gives rise to a six-membered ring ylide or diazonium betaine intermediate. Otherwise, β-hydride elimination by an intermediate carbene or rhodium-carbenoid becomes the preferred, if not exclusive, decomposition mode. However, unusual behaviour is encountered with the diazo amido ester 3d in that its rhodium(II)-induced decomposition results in the preferential formation of the α-hydroxy ester 19.

2(3H)‐Oxazolones from α‐Hydroxy Amides and Keteneylidenetriphenylphosphorane via a Phoshorus Ylide Cascade

AbstractUpon heating in xylene α‐hydroxyamides 3 react with the cumulated phosphorus ylide 1 to give the substituted 2(3H)‐oxazolones 8 in 40–80% yield. The reaction proceeds via an addition/cyclization/intermolecular‐Wittig olefination sequence, which implies three different types of phosphorus ylides of increasing “ylide activity”. Evidence for the proposed mechanism is provided by trapping the intermediate ylide species with suitable carbonyl compounds. This technique may also be used to exclusively prepare the 2,4‐oxazolidinediones 13 in good yields.

Formation of 5-Alkoxy-2-aminooxazoles and Their Novel Reactivity: Equilibrium with Nitrile Ylide

Abstract The Rh2(OAc)4-catalyzed reactions of diazoacetates with diisopropylcyanamide gave 5-alkoxy-2-aminooxazoles. Their isolation was achieved by introduction of a bulky alkoxy group at 5-position. The 5-alkoxy-2-aminooxazole reacted with methanol to give a 1 : 1-adduct in a quantitative yield. The kinetic study indicates that this reaction proceeds in a stepwise mechanism including an equilibrium of the 5-alkoxy-2-aminooxazole with a nitrile ylide intermediate.

Facile generation of aziridines from the reaction of α-diazoamides with tethered oximino-ethers

In an attempt to prepare azomethine ylide intermediates for cycloaddition reactions with electron deficient olefins, oximino-ethers with tethered α-diazoamide moieties were reacted in the presence of metal catalyst. The reaction resulted in aziridine formation preferentially.

Three-carbon ring-enlargement of ethereal oxonium ylides—a viable synthesis of medium-sized cyclic ketoethers

eight- to eleven-membered cyclic ketoethers are synthesized in a single-step by rhodium(II)-catalysed three-carbon ring-enlargement of diazoacetonyl-substituted cyclic ethers via bicyclic ethereal oxonium ylide intermediates.