Cyclopropenations ester

The trans-esters react much faster than the dy-isomers. In the case of compounds unsubstituted at C-3, stable cyclopropene esters are not formed even when lithium dialky-lamides are used as bases28. 

Many cyclopropenes unsubstituted at C(3)are unstable and nucleophilic addition to the n bond often occurs. Cyclopropene esters 44 are not capable of isolation even when lithium dialkylamides are employed to effect the dehydrohalogenation reaction. Recent... 

Long-chain cyclopropenes and cyclopropene esters are produced upon photolysis of a,j5-unsaturated epoxides as illustrated by equation 27. Whilst vinylcarbenes are the... 

Cyclopropene esters give aminobicyclo[2.1.0]pentane derivatives, which can undergo ring-opening reactions to cyclopentenes For example, methyl 3,3-dimethylcyclo-propene-l-carboxylate (37), obtained by photolysis of the corresponding pyrazolinic derivative, reacted with the diquinanic enamine 36 to give a mixture of the alkylation product 38 and the [2 + 2] cycloadduct 39 which, on acid treatment, was transformed into the triquinanic cyclopentene alcohol 40 (equation 6). 

A popular method is to analyse the total fatty acid methyl esters by CjC after reaction with silver nitrate/anhydrous methanol for 2 h at 30°C (Bianchini, Ralaimanarivo and Gaydou, 1981 Eisele et aL, 1974 Gaydou, Bianchini and Ralaimanarivo, 1983 Ralaimanarivo, Gaydou and Bianchini, 1982). Most fatty esters remain unchanged, but cyclopropene esters are converted to later-eluting methoxy ether derivatives and small amounts of ketone derivatives. Two partially resolved peaks, those from sterculic acid eluting later, are observed for each type of derivative from each cyclopropene acid and can be quantified and used to determine the proportion of sterculic and malvalic acids in the untreated oil. Verification of the identities of the acids can be determined from GC-MS of the methyl esters of the products (Ahmad et al., 1979 Eisele et ai, 1974) but prominent allylic ions in the mass spectra of the DMOX derivatives of the methoxy ethers are more readily interpretable to reveal the positions of the cyclopropene rings (Spitzer, 1995). 

The above two consecutive transformations provide straightforward access from propargyl alcohols to cyclopropene derivatives with an a- or /1-hydroxy group. This simple method is complementary to the access to 3-hydroxymethylcyclopropenes, via Rh2(OAc)4 catalyzed addition of diazoacetate to alkynes followed by reduction of the ester group, a route that is restricted to the access of primary cyclopropenyl alcohols [57], and is an alternative to the use of 2,2-dibromo-l-chlorocyclopropane via cyclopropenyl Uthium. 

Alkinyloxy)diazoacetic esters 11 give rise to product mixtures that could be separated only partially. The isolated products result from a tandem intramolecular cyclopropenation/cyclopropene —> vinylcarbene isomerization (12, 14) and from a twofold intermolecular (3+2)-cycloaddition of the intact diazo compound (13). 

Ethyl diazopyruvate, under copper catalysis, reacts with alkynes to give furane-2-carboxylates rather than cyclopropenes u3) (Scheme 30). What looks like a [3 + 2] cycloaddition product of a ketocarbenoid, may actually have arisen from a primarily formed cyclopropene by subsequent copper-catalyzed ring enlargement. Such a sequence has been established for the reaction of diazoacetic esters with acetylenes in the presence of certain copper catalysts, but metallic copper, in these cases, was not able to bring about the ring enlargement14). Conversely, no cyclopropene derivative was detected in the diazopyruvate reaction. 

The photolysis of the furan derivatives 78 yielded the butadienals 79 as the main products [123], Further isomerizations leading to allenic esters used the radiation of a cyclopropene-1 -carboxylic acid ester [124] or applied flash vacuum pyrolysis to 3 -ethoxy cyclobut- 2-en-l-one[125]. 

A carbene has been generated at position 3 of the bislactim ether derived from cyclo(L-Val-Gly) via the lithio derivative and the diazo compound. The carbene has been trapped by an acetylene to provide a cyclopropene [88AG(E)433]. Hydrolysis with 0.1 N HC1 leads to the cyclopropene aminoacid esters (Scheme 70). 

Besides the activation of the olefinic partner by a metal, the unfavorable thermodynamics associated with the addition of an enolate to a carbon—carbon multiple bond could be overwhelmed by using a strained alkene such as a cyclopropene derivative286. Indeed, Nakamura and workers demonstrated that the butylzinc enolate derived from A-methyl-5-valerolactam (447) smoothly reacted with the cyclopropenone ketal 78 and subsequent deuterolysis led to the -substituted cyclopropanone ketal 448, indicating that the carbometallation involved a syn addition process. Moreover, a high level of diastereoselectivity at the newly formed carbon—carbon bond was observed (de = 97%) (equation 191). The butylzinc enolates derived from other amides, lactams, esters and hydrazones also add successfully to the strained cyclopropenone ketal 78. Moreover, the cyclopropylzincs generated are stable and no rearrangements to the more stable zinc enolates occur after the addition. 

Cyclopropanecaiboxylic acid, 56, 70 Cyclopropanes, em-dihalo, 56, 32 Cyclopropanone ketals, 58, 40 Cyclopropenes, 58, 40 CYCLOPROPENONE, 57, 41 CYCLOUNDECANONE, 56, 107 Cycloundecanone, 2-hydroxy-, 56, 110 Cycloundecene, 1-caiboxy-, 56, 111 Cycloundecene, 1-methoxy-, 56, 111 1-Cycloundecene-l-carboxylic acid, methyl ester, 56, 108... 

The Rh(II)-catalyzed reaction has been further extended to enantio-selective cyclopropenation of alkynes by diazo esters (Scheme 96) (230). The yield and selectivity are moderate, but optically active cyclopropenes are otherwise very difficult to obtain. An interesting double stereodifferentiation is seen in the reaction of (+)- or (—)-menthyl diazoacetate. 

The intermediacy of >/2-cyclopropene complexes of nickel has been proposed in catalyzed 2+1 reactions of free cyclopropene with electron-poor olefins, to give vinylcyclo-propanes. For example, the reaction of fumarate esters with 3,3-disubstituted cyclopropenes in the presence of Ni(COD)2 catalyst gave vinyl-substituted trans-2,3-cyclopropane dicarboxylate esters (equation 235)72 302. However, when maleic esters were used instead, a mixture of both cis and trans vinylcyclopropane diesters is obtained. 

Perkin1 attempted to prepare a cyclopropene acid by eliminating two molecules of hydrobromic acid froiL,y,di. ethyldibroiuglutar c ester. All the reagents which he tried failed to give h-u. the desired product, an ethoxy derivative (I) being forced, instead. 

The meso-ionic l,3-oxazol-5-ones show an incredible array of cycloaddition reactions. Reference has already been made to the cycloaddition reactions of the derivative 50, which are interpreted as involving cycloaddition to the valence tautomer 51.21 In addition, an extremely comprehensive study of the 1,3-dipolar cycloaddition reactions of meso-ionic l,3-oxazol-5-ones (66) has been undertaken by Huisgen and his co-workers.3-39-45 The 1,3-dipolarophiles that have been examined include alkenes, alkynes, aldehydes, a-keto esters, a-diketones, thiobenzophenone, thiono esters, carbon oxysulfide, carbon disulfide, nitriles, nitro-, nitroso-, and azo-compounds, and cyclopropene and cyclobutene derivatives.4 In these reactions the l,3-oxazol-5-ones (66)... 

Functionalized cyclopropenes are viable synthetic intermediates whose applications [99.100] extend to a wide variety of carbocyclic and heterocyclic systems. However, advances in the synthesis of cyclopropenes, particularly through Rh(II) carboxylate—catalyzed decomposition of diazo esters in the presence of alkynes [100-102], has made available an array of stable 3-cyclopropenecarboxylate esters. Previously, copper catalysts provided low to moderate yields of cyclopropenes in reactions of diazo esters with disubstituted acetylenes [103], but the higher temperatures required for these carbenoid reactions often led to thermal or catalytic ring opening and products derived from vinylcarbene intermediates (104-107). 

Cycloaddition reactions of phenyl and tosyl azides to the strained double bond in cyclopropenes have been investigated.170il The reaction products from 3,3-dimethylcyclopropene indicate that the initially formed intermediate is a normal 1,3-dipolar adduct. Tetrachlorocyclopropene yields the primary adducts with several aryl azides. 70b However, cyclopropenedicarboxyl ester gives only unstable triazolines with phenyl and methyl azides.170 ... 

Dirhodium(II) tetrakis(carboxamides), constructed with chiral 2-pyrroli-done-5-carboxylate esters so that the two nitrogen donor atoms on each rhodium are in a cis arrangement, represent a new class of chiral catalysts with broad applicability to enantioselective metal carbene transformations. Enantiomeric excesses greater than 90% have been achieved in intramolecular cyclopropanation reactions of allyl diazoacetates. In intermolecular cyclopropanation reactions with monosubsti-tuted olefins, the cis-disubstituted cyclopropane is formed with a higher enantiomeric excess than the trans isomer, and for cyclopropenation of 1-alkynes extraordinary selectivity has been achieved. Carbon-hydro-gen insertion reactions of diazoacetate esters that result in substituted y-butyrolactones occur in high yield and with enantiomeric excess as high as 90% with the use of these catalysts. Their design affords stabilization of the intermediate metal carbene and orientation of the carbene substituents for selectivity enhancement. 

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