2.3- allenoic acid

The addition reaction of HBr to 2,3-allenoic acids afforded 2-bromo-2-propenoic acid [251],... 

This approach is applicable to cross-coupling reactions of allenoic acids and acrolein, which lead to the synthesis of lactones (Scheme 16.98) [104]. The reaction proceeds via oxypalladation of an allenoic acid to give rise to a vinylpalladium species. 

Scheme 16.98 Cross-coupling reaction of an allenoic acid and acrolein.

The formation of 2 furane rings was achieved in one transformation by Ma and co-workers. Allenoic acids and allenyl ketons were reacted in the presence of a palladium catalyst to give the unsymmetrical bifuryl product, arising from the cyclization of both allene derivatives mediated by the same palladium centre followed by their coupling (3.73.) 91... 

Allenyl ketones can also be cross-coupled with allenoic acids to give 2,4-disubstituted furans <2002AGE1775> or with allenamides to yield 4-(3 -furanyl)-2(5//)-furanimines <2005JOC6291>. With chiral allenoic acid derivatives, 4-(3 -furanybbutenolides can be synthesized stereoselectively with complete chirality transfer (Equation 47) <2004CEJ2078>. 

Typical procedure To a solution of diaryl ditelluride (0.50 mmol) in dry MeCN (2 mL) under Nj was added dropwise SO2CI2 (0.081 g, 0.60 mmol) and the mixture was stirred at room temperature for 1 h. a-Allenoic acid (0.50 mmol) in dry MeCN (2 mL) was then added to above ArTeCl solution with stirring. After the reaction was complete, the mixture was concentrated and the residue purified by flash chromatography or preparative TLC to afford j8-organoteUurobutenolides. 

Propargylic mesylates are converted to the transposed 2,3-alkadienoic esters and amides by (PhjP) Pd and CO in the presence of alcohols and arylamines, respectively. These allenoic acid derivatives are precursors of butenolides. In a synthesis of kallolide-B, this reaction is the critical step (PhjP) Pd is generated in situ from (dba)3Pd2 and PhjP in the presence of carbon monoxide. ... 

Kang et al. showed that under the catalysis of Pd(PPh3)4 (5 mol%) the reactions of 4,5- or 5,6-allenyl alcohols/toluenesulfonamides and 4,5- or 5,6-allenoic acids with hypervalent iodonium salts led to the formation of five- or six-mem-bered-ring heterocyclic products (Schemes 22 and 23) [15, 16]. With AT-(3,4-pentadienyl)toluenesulfonamide, a mixture of four- and six-membered-ring products was also formed. 

Backvall et al. demonstrated the Pd(II)-catalyzed cyclizations of 4,5- or 5,6-allenoic acids 45,3,4- or 4,5-allenols 47, and 4,5-allenyltoluenesulfonamides 49 with LiBr (Scheme 25). The reaction was initiated with bromopalladation of the allene moiety affording a 2-bromo-substituted 71-allylic palladium intermediate, which underwent intramolecular nucleophilic substitution to afford the heterocyclic products and Pd(0) (pathway 1, Scheme 1). The in situ generated Pd(0) was oxidized to the catalytically active Pd(II) species by its reaction with benzoquinone [18]. 

Tanaka et al. established the chemistry of using the bromoallene moiety as the equivalent of allyl dications.This dication can react with an intermolecular nucleophile (MeOH) and an intramolecular nucleophile to form heterocyclic alkenes (Scheme 26) [19]. The PdCl2-catalyzed reaction of 2,3-allenoic acids 58 with allylic halides in DMA at 50 °C afforded 4-allylic-substituted 2(5Tf)-fura-nones 59 in moderate to excellent yields (Scheme 27) [20]. 

Pd(OAc)2 can catalyze the reaction of 2,3-allenoic acids with non-allylic alkenyl bromides with a terminal C=C bond leading to P-alkenyl butenolides 61 and 62 (Scheme 29). The reaction proceeded via oxypalladation-carbopal-ladation, repeated P-dehydropalladation/hydropalladation-dehalopalladation, in which Pd(II) is the catalytically active species [21]. 

We have demonstrated the first example of oxidative dimeric cyclization between two different classes of allenes, i.e., 2,3-allenoic acids and 1,2-allenyl ketones. The product is a dumb-bell-type bicyclic product 4-(3 -furanyl)-butenolide71 (Scheme 33) [24]. 

From optically active 2,3-allenoic acids the corresponding optically active butenolides can be prepared in high yields and ee values. In this reaction excess... 

Recently, Ma and Shi reported a one-step procedure for the efficient synthesis of butenolides via a Pd(0)- and Ag -cocatalyzed carbopalladation-cyclization sequence of aryl/aUcenyl halides with the easily available 3-substituted allenoic acids (Scheme 38). In this reaction the presence of a catalytic amount of Ag is crucial, although its exact role is still unclear. ... 

SCHEME 69 Synthesis of polysubstiluted chromones by aryne reaction with allenoic acids [95]. 

SCHEME 6.91 Cascade reaction of 2,7-aIkadiynylic carbonates with 2,3-allenoic acids. 

Since 2002, Ma et al. have demonstrated the cross-coupling/cyclization of 2,3-allenoic acids 346 in the presence of other functionalized allenes, such as 1,2-allenyl ketones 368 [121] or 2,3-allenols 370 [122], affording differently substituted 2(5/f)-furanones 369 and 371. They also studied the cascade cycUzation/cross-coupling reaction of 2,3-allenoic acids in the presence of simple monosubstituted allenes, which yielded the stereodefined 4-(bromo-2( )-alken-2-yl)-2(5 0furanones Z-372 [123] (Scheme 6.94). 

SCHEME 6.96 Pd-catalyzed cyclization reaction of 2,3-allenoic acids with 1,5-bisallene. 

R. erythropolis AJ270 2,3-Allenenitriles (R) -2,3-Allenamides (S) -2,3-Allenoic acids Chemoenzymatic synthesis of functionalized heterocyclic compounds [107]... 

Ao, Y.-R, Wang, D.-X., Zhao, L., and Wang, M.-X. (2014). Biotransformations of racemic 2,3-allenenitriles in biphasic systems Synthesis and transformations of enantioenriched axially chiral 2,3-allenoic acids and their derivatives. Journal of Organic Chemistry, 79, 3103-3110. 

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