Propargylic acid

Takasu, Ihara and coworkers described an efficient synthesis of ( )-paesslerin A (4-73) using a combination of a [4+2] and a [2+2] cycloaddition (Scheme 4.16) [25], Reaction of 4-71 and propargylic acid methyl ester in the presence of the Lewis acid EtAlCl2 led to 4-72 in 92 % yield, which was converted in six steps into the desired natural product 4-73 by transformation of one of the ester moieties into a methyl group, hydrogenation of one double bond, removal of the other ester moiety, and exchange of the TIPS group for an acetate. 

Steric effects and FMO control have been combined in an elegant way to achieve regiospecific synthesis of pyrazole inhibitors of dihydroorotate dehydrogenase <2006SL901>. When the size of the propargylic acid ester 86 is increased from ethyl to diphenylmethyl, pyrazole 87 is formed from compound 85 regiospecifically (Scheme 3 Table 4) <2006H(68)1007>. 

The oxidation of the primary hydroxyl groups in 3-phenyl-2-lV-acetylamino propanol and propargylic alcohol by electrogenerated chromic acid has been reported. jV-Acetylphenylalanin and propargylic acid are both formed in 90% current yield. 

Equally, in presence of A1C13, if N,N-diethyl-carbamoyl chloride is applied to an l-alkyl-2-TMS-acetylene, the corresponding propargylic acid amide 56 can be isolated52 (see Scheme 6). 

We have also prepared a propargylic acid derivative of the pentapeptide enkephalin (see below), which was reacted, after cleavage and purification, with Co2(CO)g in solution to yield the Co2(CO)6(alkyne) derivative [31]. Similarly, other Co2(CO)6 alkynyl peptides were synthesized from the preprepared peptide and Co2(CO)g in solution (see Sect. 2.2.2 and the section below on biological activity) [32]. In a related fashion, the Co2(CO)6 moiety can also be introduced C-terminally (see Sect. 2.2.3) or internally (see Sect. 2.2.2). 

Variation of the Procatalyst (Metal Component) and the Acetylenic Substrate. The in situ catalysts Co(acac)3-Et2AlCl-phosphine have proven to be well-suited for the synthesis of 4-aryl- and 4-alkyl-substituted deltacyclenes. The catalysts tolerate remote oxygen functionalities in the acetylenic substrate. However, they could not be used with functionalized acetylenes such as propargylic acid derivatives. 

Hydrolysis yields the terminal acetylene (3) carbonation yields the propargylic acid (4). Synthesis of a wide variety of acetylenes is possible by the reaction of the intermediate lithium acetylides with other electrophiles (alkyl halides, aldehydes, ketones). 

A terminal alkyne can be converted to the anion under electrolytic conditions, in the presence of CO2, to give propargylic acids, R—C=C—COOH. ... 

Under the same conditions even free alkynyl aldehydes undergo a 1,4-addition to propargylic acid esters (eq. (6)) [14]. 

Carlson and Olger have reacted the dilithium salt of propargylic acid with oxiranes and shown that the resulting 8-hydroxycarboxylic acids could be cyclized wiA solvation to 5,6-dihydro-2-pyrones (Scheme 14). The method was subsequently used in a neat synthesis of pestalotin (R = Bu"CHMe). 

Menthadien-8-ol (558) has been reported as a new natural product from olibanum resin. This compound had already been synthesized in a routine manner by Hoppmann and Weyerstahl in 1974, from the methyl ester of 4-methyl-1,4-cyclohexadienecarboxylic acid (from isoprene and propargylic acid). ... 

D. Inactivation of Pyravate Formate-Lyase by Propargylic Acid. 378... 

Since thiols and thiyl radicals are known to readily undergo addition reactions at unsaturated carbon centers (199, 202, 204), a possible mechanism for this inactivation reaction is shown in Scheme 43. Addition of the active site nucleophilic or radical species followed by protonation or electron transfer, respectively, would yield the thioacrylate derivative and inactive enzyme. Of course, addition to C-2 of propargylic acid is also possible, forming a 2-substituted acrylate derivative instead. 

Acetylenecarboxylic acid Carboxyacetylene EINECS 207-437-8 NSC 16152 Propargylic acid Propiolic acid Propynoic acid 2-Propynoic acid. Used in chemical synthesis, mp 9° bp = 144 (dec), bp50 = 70-75 1.1380 very soluble in H2O, EtOH, Et20,... 

Monomers with unprotected alkyne groups in the side chain cannot be polymerized without side reactions, as the alkylidene catalyst will engage in a competing alkyne metathesis. This side reaction can be avoided by using monomers with alkyne groups either complexed with di-cobalt octacarbonyl 1 or TMS-protected 2 (Scheme 9.3a,b) [14, 35, 36]. Alkyne incorporation at the chain end was achieved in a post-functionalization approach, reacting hydroxyl-terminated polynorbornene (PNBE) 5 with propargylic acid 6 (Scheme 9.3c) [37]. 

Figure 10.11 Macrocyclization of peptides by click chemistry between propargylic acid residues and an azide- functionalized amino acid...

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