Cumulenes esters

Pyrrolizin-3-ones may also be obtained by FVP of 3-(pyrrol-2-yl)propenoate esters such as 62, 69, and 74. Also, benzo-annulated pyrrolizinone 17 was obtained by FVP of 2-(tf-methoxycarbonyl phenyl (pyrrole <1999J(P1)2047>. FVP of alcohols 77, 78, and 79 led to 3//-pyrrolyzine derivatives 1, 192, and 193, respectively, in good yields (66-95%). These transformations proceed by elimination of water and subsequent electrocyclization of the in situ-generated cumulene (Scheme 44) <1999J(P1)2049>. 

If allenes bear a potential leaving group in the a-position to the cumulene system, they are very attractive substrates for palladium-catalyzed substitutions. Examples are a-allenic acetates and particularly a-allenic phosphates, which react under palladium(O) catalysis with carbanions derived from /3-diesters, /i-keto esters, a-phenylsulfonyl esters and glycine ester derivatives. They lead to /3-functionalized allenes such as 86, 89 and 93 (Eqs. 14.9-14.11) [45 18]. 

Conyza canadensis (L.) Cronq. Xiao Fei Peng (aerial part) Essential oils, matricaria ester, dehydromatricaria ester, linoleyl acetate, limonene, linalool, centaur X, dephenyl methane-2-carboxylic acid, cumulene, O-benzylbezoic acid.48 Relieve swelling, itchiness, treat intestine and liver infection, a detoxicant, externally for skin eczyma, wounds, pain caused by arthrritis, toothache. 

Significant mechanistic insights into the DABCO-catalysed isomerization of y-hydroxy-o ,/3-alkynyl esters to y-oxo-a,p-trans-alkenyl esters have been reported.33 The reaction mechanism involves cumulene formation, protonation with the conjugate acid of the amine, and protonation of the resulting allenol with water. 

As a model reaction for the phototoxic membrane damage by PHT, PHT was photolyzed with unsaturated fatty acid, undecylenic acid methyl ester, and isolated four major photoadducts (54-57) as shown in Scheme 18 [60]. PHT was also irradiated with 1-hexene as a reference reaction [32]. Photoreactions occur through the [2+2] photocycloaddition reaction between double bonds of olefins and C1-C2, C3-C4, and C5-C6 triple bonds of PHT. These reactions most likely result from the cumulene type diradical species. 

A first preparation of cumulene (buta-2,3,4-triene)-carboxylic acids (50) features condensations between the anion (49) and ketones or a-keto-esters, the latter electrophiles leading to cumulene diacids (Scheme 8)Thermolysis of these acids can be used to prepare [4]radialenes. 

There are reported numerous examples of the syntheses of dihalocyclo-propanes via addition of PTC-generated dihalocarbenes to unsaturated compounds such as alkenes, unconjugated and conjugated di- and polyenes, allenes, cumulenes functionalized alkenes such as haloalkenes unsaturated ethers, acetals, and ketals esters of imsaturated alcohols alkenes substituted by sulfur, nitrogen, silicon atoms some unsaturated carbonyl compounds, etc (eqs. 108-114). 

Palladium-catalyzed substitutions of allylic esters 129, which proceed via intermediate 7t-allylpalladium complexes such as 130, are well estabhshed [334]. In contrast, the reactions proceeding through [t-allylpalladium intermediates, generated by addition of the palladium a-complex intermediates from haloarenes, haloalkenes, or corresponding triflates, to allene and substituted allenes 131 (Scheme 8.30) have scarcely been tapped [153]. Recently, higher cumulenes have been reported as suitable alkenes in Heck reactions [335],... 

Sorensen, N. A., and K. Stavholt A Hexahydro Matricaria ester — Composit-Cumulene 1 from Scentless Mayweed Matricaria inodora L.). Acta Chem. Scand. 4, 1080 (1950). 

Alper and coworkers successfully exploited the cydocarbonylation reactions of o-iodophenols 1, 2-hydroxy-3-iodopyridine 2, and o-iodoanilines 3 with heterocumu-lenes, giving rise to benzo(e]-l,3-oxazin-4-one 4, pyrido[3,2-e]-l,3-oxazin-4-one 5, 4 (3H)-quinazolinone 6, and 4(3H)-quinazolindione 7 derivatives (Scheme 13.2) (21,22]. The reactions proceed in the presence of equimolar amount of palladium acetate and a bidentate phosphine ligand (dppb or dppf) and a base (i-Pr2NEt or K2CO3), in benzene or THF at 80-100 °C under a pressure of 20 atm of carbon monoxide. Carbodumides, isocyanate, and ketenimines were used as cumulenes, and good regioselectivities were achieved with unsymmetrical reactants. The reaction mechanism is beheved to involve in situ formation of a carbamate ester or urea-type intermediate followed by palladium-catalyzed carbonylation and cyclization to yield the products. 

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