Allene acidity

Conjugated terminal fluoroenynes add water to the double bond at -5 C to form a-fluoro allemc acid fluondes. At 20 C, the allenic acid fluorides and concentrated sulfunc acid give y- and 8-laaones (equation 1) In the presence of concentrated sulfuric acid, conjugated nontermmal fluoroenynes add water to the triple bond and then to the double bond to form a-fl uoro-P-diketones and exocyclic a-fluoroenones [/] (equation 2). 

Scheme 4.48 Asymmetric synthesis of/i-allenic acids 184,186 and (-)-malyngolide 187 via /Mactones.

Intramolecular [4 + 2]-cycloaddition reactions of allenic acids and esters proceeded in refluxing toluene to give bicyclic compounds with the exo-isomer predominating (Table 12.9) [120]. When a Lewis acid was used as a promoter, the [4 + 2]-cydoaddi-tion occurred at 0 °C and the endo-isomer was favored. 

Table 12.9 Cycloaddition reactions of allenic acids and esters.

Allenic acylureas 152, prepared in situ from the corresponding allenic acid 151 and carbodiimides, afforded lactams in good yields [126]. 

The efficiency of chirality transfer of chiral 2,3-allenic acids can be much increased by switching the Jt-allylpalladium mechanism to a coordinative cycliza-tion-reductive elimination route (Scheme 16.25) [30]. 

Tellurolactonization of Ct-allenic acids with phenyltellurenyl chloride... 

The hydrobromination of functionally substituted allenes has received little attention. Vinylic allenes generate mixtures of bromides,76 while tetrafluoroallene affords the allylic bromide,83 and allenic acids produce 3-bromo-3-alkenoic acids (equation 109). 37,138... 

The reaction of /V-cyclohexyl-/V-(2-pyridyl)carbodiimide and the allenic acid 83 in dry tetrahydrofuran at ambient temperature for 3 days afforded a 2 1 mixture of isomeric 2-oxo-2H- and 4-oxo-4/7-pyrido[l,2-a]pyrimid-ines 88 and 87 instead of the expected Diels-Alder adduct (92HCA1262). The formation of an activated ester 84 was suggested in the first step, which underwent a 1,5- or 1,3-acyl migration, giving rise to the isomeric pyrido(l,2-a]pyrimidines 87 and 88 via acylureas 85 and 86, respectively (Scheme 6). 

For example, the copper catalyzed addition of Grignard compounds to alkynyl substituted /(-lactones 55 delivers /S-allenic acids 56 in high yields [38], During these reactions, the central chirality of one of the stereogenic centers of the /Mactone is transferred to the axial chirality of the allene. 

Stereocontrolled conjugate addition of lithium dimethylcuprate to the electron deficient 2,3-double bond of allenes 851 leads to 5,6-dihydropyranM-oncs 852 in moderate yield (Equation 343) <2000J(P1)3188>. Similarly, the Ag(l)-catalyzed intramolecular cyclization of the allenic acid 853 is accelerated upon addition of diisopropylethyl-amine to afford the 3,6-dihydropyran-2-one 854, an intermediate during the total synthesis of (—)-malyngolide (Equation 344) <2000JA10470>. 

Lithium dimethylcuprate is less selective than dimethylcadmium in its reaction with a steroidal allenic acid fluoride (88). Whereas the cadmium compound in refluxing benzene solution reacts mainly with the... 

The reaction of allenic acid 500 with carbodiimides affords tricycloundecatrienones 502. The reaction proceeds through (he initially formed linear N-acylurea derivative 501." ... 

Allenic acids. Reaction of 17ix-difluorocyclopropenyl-5(x-androstane-3jS,l7/ -diol 3-acetate (1) with the reagent in dry methylene chloride affords a mixture of three isomeric products (2 4). 

Treatment of the cydopropenonecarbinol (5) with the fluoramine gives the allenic acid fluoride (6) in 80° , yield. Treatment of (6) with sodium methoxide in methanol... 

The reactions thus afford a method for synthesis of allenic acids and jS-keto esters. 

For the racemic allenic acid (133), each enantiomer is r uced stereospecifically to give the alkenoic acid diastereomers (134) and (135) (Scheme 63). In contrast, the levels of enantiomeric discrimination observed in microbial reductions of allenic alcohols have so far been very low. ... 

The catalytic pair Ni(CN)2/Bu4N Br readily catalyzes the biphasic carbonyla-tion of a-haloalkynes [144, 145] and allenyl halides [145]. The first reaction results in a mixture of allenic monoacids and unsaturated diacids, whereas allenyl halides transform to allenic acids with high regioselectivity. The carbonylation of gem-dibromocyclopropanes under PTC conditions is catalyzed by Ni" and Co" salts. The reaction gives the corresponding cyclopropanecarboxylic acids in fair yields [146]. 

ALLENIC ACIDS Diethyl(2-chloro-l,1,2-trifluoroethyl)amine. 

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